cost efficiency of the design plans for the market street drainage improvements project

Running head: COST EFFICIENCY OF THE MARKET STREET TUNNEL 1

Cost Efficiency of the Design Plans For

The Market Street Drainage Improvements Project

Katie Kassouf

Academic Magnet High School

COST EFFICIENCY OF THE MARKET STREET TUNNEL 2

Abstract

Since its establishment, the City of Charleston, South Carolina, has sought to develop an

efficient drainage system to relieve its downtown streets from flash flooding. Urban flooding

occurs most frequently during the summer months and can result from periods of high tide and

heavy rain. To alleviate this problem, the City of Charleston launched the Market Street

Drainage Improvements Project in an effort to install stormwater drainage networks in the

downtown area. Through this study, the researcher will evaluate the cost efficiency of Division II

of this project in terms of the money saved by the City of Charleston.


Table of Contents

Cost Efficiency of the Design Plans For ......................................................................................... 4

The Market Street Drainage Improvements Project ....................................................................... 4 Statement of Need ........................................................................................................................... 4 Main Goal ....................................................................................................................................... 6

Methods........................................................................................................................................... 7 Significance..................................................................................................................................... 8

Applicability.................................................................................................................................... 9 Chapter II: Review of Literature ................................................................................................... 10 Constructing Flood Relief Systems for the City of Charleston .................................................... 11

Initial Drainage Design: Network of Brick Arches ................................................................... 11 Sanitation System Improvements and the Plum Island Wastewater Treatment Plant ............... 13

Development and Deterioration of the Original Cooper River Tunnel ..................................... 14 Emergency Sewer System Replacement Program .................................................................... 16 1984 Master Drainage and Floodplain Management Plan by Davis & Floyd, Inc. .................. 17

Calhoun Street East Drainage Improvements Project ............................................................... 19 Market Street Drainage Improvements Project ......................................................................... 20

Division III : Spring/Fishburne Drainage Project ..................................................................... 24 Change Order for the Design of the Market Street Tunnel........................................................... 27

Increased Depth of the Market Street Tunnel............................................................................ 28

Decreased Slope of the Market Street Tunnel ........................................................................... 35 Connection to Concord Street Pump Station vs. Calhoun Street Tunnel .................................. 38

Final Lining of the Market Street Tunnel .................................................................................. 39 Elimination of Ground Freezing at Junction of Market Street and Calhoun Street Tunnels .... 40

Chapter III: Methods ..................................................................................................................... 43

Materials........................................................................................................................................ 44 Procedures ..................................................................................................................................... 44

Evaluation ..................................................................................................................................... 46 Conclusion .................................................................................................................................... 46 Chapter IV..................................................................................................................................... 47

Increased Depth of the Market Street Tunnel ............................................................................... 47 Decreased Slope of the Market Street Tunnel .............................................................................. 54

Connection to Concord Street Pump Station vs. Calhoun Street Tunne l ..................................... 55 Final Lining of the Market Street Tunnel ..................................................................................... 57 Elimination of Ground Freezing ................................................................................................... 58

Total Savings................................................................................................................................. 59 Chapter V ...................................................................................................................................... 60

Principal Findings and Interpretation of Data............................................................................... 60 Implications................................................................................................................................... 61 Limitations .................................................................................................................................... 62

Summary ....................................................................................................................................... 62 References ..................................................................................................................................... 64


Cost Efficiency of the Design Plans For

The Market Street Drainage Improvements Project

Since its founding, the City of Charleston, South Carolina, has struggled to find a

solution to the excessive flooding that plagues its downtown streets. Urban flooding results from

a combination of high tides, heavy rain, near sea level elevation, flat topography, and a lack of

adequate drainage systems in the downtown area (Cabiness, Kirk, O’Connell, & Swartz, 2012).

Furthermore, Charleston is part of the Low Country, a region consisting of “low-lying terrain”

that naturally retains an “abundance of water” due to its proximity to the Atlantic Ocean (GORP,

2010, p. 1). The Low Country’s table-top topography and close-to sea level elevation prevent

accumulated surface water from draining quickly; thus, an event as minor as a high tide can

potentially “result in hours of standing water” (Cabiness et al., 2012). The most severe flooding

occurs in the downtown areas closest to Charleston Harbor when heavy rain coincides with high

tidal events (O’Connell, 2013). Such flooding poses health hazards to drivers, pedestrians, and

residents in the Charleston area. Although several different drainage systems have been

implemented in Charleston since the mid-1800s, none of them have proven adequate. Hence, the

City of Charleston launched the Market Street Drainage Improvements Project in 2006 to combat

problematic downtown flooding (Kirk, n.d.-a). Ultimately, this thesis will examine the cost

efficiency of this current design in terms of the money saved by the City of Charleston during the

course of the project.

Statement of Need

Simply stated, stormwater is excess ground surface water created by events such as heavy

rains and high tides; furthermore, large concentrations of stormwater can produce flooding in

areas that do not possess adequate drainage infrastructure. Since the mid-1800s, several types of


stormwater collection systems have been implemented in Charleston to decrease regional

flooding. As early as 1837, solutions to this problem were prompted by the mayor’s offer of a

$100 gold piece for the best proposed flood relief system (Slade, 2013). Following this generous

proposition, city engineers constructed the first drainage design ever attempted in Charleston: a

network of brick arches installed in the downtown area (O’Connell, 2013). Although this system

provided minimal flood relief, it did not prove efficient for the City of Charleston because of its

small size (Drolet, Cabiness, Swartz, & O’Connell, 2012). City engineers continued to struggle

with inadequate designs for several years. Then, in 1984, Davis & Floyd, Inc., produced a Master

Plan to improve the city’s stormwater collection systems. Unlike the network of brick arches, the

1984 Master Plan divided and directed Charleston’s stormwater into catch basins situated around

the city (O’Connell, 2013). In 1997, Davis & Floyd, Inc., in association with URS Corporation,

initiated preparations for a key component of this Master Plan, called the Market Street Drainage

Improvements Project (O’Connell, 2013). City officials selected a deep tunnel system as the

design for this project to protect the urban and historic structures surrounding the proposed

project location, an intersection in downtown Charleston. Specifically, a deep tunnel system is a

network of large, underground sewers that stores excess water until it can be released at a desired

location (Milwaukee Metropolitan Sewer District, n.d.). However, a lack of funding prevented

the city from launching Division I of this project until 2006 (Kirk, n.d.-a). In July 2012, city

officials awarded the contract for Division II to the joint venture of Triad Midwest Mole

(O’Connell, 2013). Upon receiving the contract for the project, the joint venture proceeded to

make several significant changes to the original construction plans for the Market Street Tunnel

to increase the safety of the tunnel installation process. While several tunneling systems have

been implemented in Charleston in the past to provide flood relief and wastewater conveyance


for the area, no cost efficiency study has been conducted on any of these construction projects to

date. Furthermore, no cost analysis has been performed for the construction of an inner-city deep

tunnel system for the Charleston area. Hence, this thesis will provide a cost efficiency analysis of

the construction methods used to install the Market Street Tunnel and will compare that data to

the projected cost of the tunnel as indicated by the original blueprints for the project.

Main Goal

The governing question for this thesis is, how have the proposed changes to the original

plans for the Market Street Drainage Improvements Project affected the cost efficiency of this

design in terms of the money saved by the City of Charleston?

The initial designs for the Market Street Tunnel were created in 1997 by Davis & Floyd,

Inc., in association with URS Corporation, to provide flood relief for downtown Charleston

(O’Connell, 2013). However, Triad Midwest Mole proposed that specific areas of the plans be

changed in order to increase project efficiency. Thus, the purpose of this study is to examine the

modifications made to the construction plans for the Market Street Tunnel and to quantify the

money the city has saved because of these alterations.

Due to Charleston’s nearly sea level elevation, flat topography, and proximity to the

Atlantic Ocean, the city experiences severe flash flooding during periods of high tide and heavy

rain (Cabiness et al., 2012). Thus, the Market Street Tunnel is being installed to help compensate

for a lack of adequate drainage systems in the downtown area. The goal of this improvements

project is to spare residents the danger of traveling on flooded roads and to improve urban health

conditions by draining stormwater from street surfaces (Slade, 2013). Additionally, this thesis

satisfies a gap in the civil engineering field by providing a detailed cost analysis on a tunneling

project in Charleston. To the best of the researcher’s knowledge, no substantial cost efficiency


study has ever been conducted for a deep tunnel system in this area. Furthermore, this thesis may

provide a point of reference for future tunnel contractors in Charleston by demonstrating how

certain construction methods can increase the economic efficiency, and ultimately the success, of

their own projects. Therefore, this thesis may prove useful to current and future experts in the

civil engineering field.

Methods

To collect data for this thesis, the researcher has performed a cost-analysis of the

construction methods used to implement the Market Street Drainage Improvements Project.

Specifically, the researcher has focused on the modifications made to the original plans by Davis

& Floyd, Inc. A cost efficiency comparison between the altered portions of the 1997 blueprints

and the corresponding sections of the current design has provided the researcher grounds upon

which to estimate the amount of money the City of Charleston has saved during the course of the

project. To substantiate this cost analysis, the researcher has collected quotes for materials,

wages for laborers, and operating and installation costs for construction equipment. In addition,

the researcher has consulted design engineers from Triad Midwest Mole to verify that the

collected data is correct. Moreover, the researcher has calculated the difference between the costs

of the proposed Davis & Floyd, Inc. plans and the modified designs by Triad Midwest Mole.

Therefore, the researcher has estimated the amount of money saved by the City of Charleston as

a result of the design alterations to the Market Street Tunnel.

This thesis is classified as a case study because it only focuses on one construction

project in the civil engineering field. Furthermore, the researcher has collected qualitative and

quantitative data and has used inductive reasoning to develop conclusions that satisfy both the

governing question and the informational gap. Qualitative data consists of the researcher’s


analysis of the engineering techniques used to modify the 1997 blueprints for the Market Street

Tunnel. These construction methods are discussed in detail and in relation to how they contribute

to the overall cost efficiency of the project. Next, the researcher has gathered all quantitative data

through a cost comparison between the revised design for the tunnel and the original system

developed by Davis & Floyd, Inc. Hence, the researcher has used these quantities to estimate the

total amount of money saved by the City of Charleston as a result of the project alterations.

The researcher has evaluated the worth of the data by confirming that they can be used to

answer the governing question. In addition, the advisor and mentor have assisted the researcher

in determining the value of the qualitative and quantitative data. The mentor’s opinion of the data

has proven especially crucial because the mentor is an expert on the topic of the Market Street

Tunnel. Furthermore, the mentor has guided the researcher in selecting the most significant

modifications to study. Ultimately, the data have been deemed successful by the researcher, the

advisor, and the mentor because they clearly explain how the modified construction methods

used to install the Market Street Tunnel have saved the City of Charleston money.

Significance

The Market Street Drainage Improvements Project is a significant area of research

because it is only the second deep stormwater tunnel system to be installed in Charleston.

Furthermore, it is Charleston’s second tunnel design to include drop shafts and a connection to a

stormwater pump station. To clarify, a drop shaft is a vertical pipe that carries water from

shallow surface drainage systems to a deeper tunnel network (Williamson, 2001). Hence, the

Market Street Tunnel itself is filling an informational gap in the civil engineering field by

confirming the overall success of the deep tunnel system as a drainage design for downtown

Charleston. Furthermore, the conclusions drawn from this study are significant as far as


application in the civil engineering field because they indicate construction methods that can be

used to improve the cost efficiency of deep tunnel projects. Thus, professional engineers could

use this thesis to improve the cost of their own tunneling techniques and to save their clients time

and money. In addition, several stormwater tunnels are currently being implemented in

downtown Charleston, and the success of the modifications made to the Market Street Tunnel

may influence the design of these developing projects. Therefore, the most important aspect of

the researcher’s study is the cost efficiency analysis of the engineering methods used to install

the Market Street Tunnel.

Applicability

The conclusions drawn through this thesis can be used by professionals within the civil

engineering field to improve the cost efficiency of their own tunneling projects. An engineer or

company could extend the implications of the researcher’s data by using similar construction

methods to decrease the cost of installing a deep tunnel system on an island or near an inland

body of water, such as a lake. Ultimately, the study will enhance the researcher’s knowledge of

deep tunnel designs and their applicability to the Charleston area.


Chapter II: Review of Literature

The Market Street Drainage Improvements Project is a tunnel system designed by Davis

& Floyd, Inc., in association with URS Corporation, to alleviate flash flooding in downtown

Charleston. The tunnel was completed by Triad Midwest Mole in 2014, and it spans parts of

Market and Concord streets. Although the term, Market Street Tunnel, applies to the deep tunnel

system as a whole, the researcher will refer specifically to the Concord Street portion as the

Concord Street Tunnel and to the Market Street portion as the Market Street Tunnel. The

researcher adopted these terms from documents composed by Triad Midwest Mole. Furthermore,

the researcher will clarify whether the discussion refers to the Concord Street section, the Market

Street section, or the entire Market Street Tunnel. Moreover, this thesis will examine the cost

efficiency of the design used for the Market Street Tunnel in terms of the money saved by the

City of Charleston. In addition, the following review of literature will investigate prior

stormwater and sewage systems implemented in Charleston, including the mid-1800s network of

brick arches in the downtown area, the development of the Plum Island Wastewater Treatment

Plant, the 1984 Master Plan by Davis & Floyd, Inc., the Emergency Sewer System Replacement

Program, and, finally, the Market Street Drainage Improvements Project. Topics that will not be

covered in this study are the cost efficiency of prior system designs, minor tunneling projects that

did not substantially impact flooding in the Charleston area, and structural alterations that were

not included in the change order submitted by Triad Midwest Mole to the City of Charleston.

Currently, there is no existing cost analysis on tunneling projects in the Charleston area;

therefore, the data collected through this thesis not only satisfies an informational gap, but also

provides a point of comparison for cost efficient versus non-cost efficient construction methods

for deep tunnel systems in the City of Charleston.


Constructing Flood Relief Systems for the City of Charleston

Beginning in the mid-1800s, the City of Charleston, South Carolina, sought to develop an

efficient drainage design to provide flood relief for its downtown streets. As aforementioned, the

most severe flooding occurs in areas closest to Charleston Harbor when heavy rain and high tides

coincide (O’Connell, 2013). Such flooding endangers the mobility and health of drivers,

pedestrians, and residents of the downtown area, as well as those working in major, local

establishments such as hospitals, schools, law firms, and banks.

To combat urban flooding, city engineers have implemented several drainage designs in

downtown Charleston. However, none of these systems has proven adequate in removing

substantial amounts of stormwater from street surfaces. One of the key challenges engineers face

when drafting and constructing drainage tunnels for the Low Country is the region’s close-to sea

level elevation (O’Connell, 2013). For drainage systems to be effective, pipelines and tunnels

must have slopes that enable them to transport excess water, via gravity, from the ground surface

to another location. However, even moderately sloped structures installed in Charleston tend to

be at or below tidal zones, thus rendering the infrastructure useless during high tides (Cabiness et

al., 2012). Thus, when the Calhoun Tunnel, a deep tunnel system, provided significant flood

relief for a part of downtown Charleston, city engineers used it as a model during the

development of the Market Street Drainage Improvements Project (Kirk, n.d.-a). Ultimately, this

thesis will examine the economic implications of this deep tunnel design in terms of the money

saved by the City of Charleston.

Initial Drainage Design: Network of Brick Arches

The first drainage design attempted in downtown Charleston was a network of brick

arches installed during the mid-1800s (O’ Connell, 2013). These arches served as an


interconnected gravity network that transported stormwater from city streets to the Cooper and

Ashley Rivers (O’ Connell, 2013). In other words, the negative slope of the drainage structure

conveying urban runoff resulted in the gravitational movement of the stormwater from the street

surface to the outfall, or terminal opening, of the pipeline. Although this system provided

minimal flood relief, it did not prove adequate for the City of Charleston because of its small size

(Drolet et al., 2012). Constructed to be five ft. wide by four ft. high, city engineers intentionally

undersized the arches to increase the scouring velocities of the system (City of Charleston, 2012 :

Drolet et al., 2012). Simply stated, they believed that a smaller drainage design would reduce

sedimentation within the system during periods of flooding or high tide. However, this theory did

not prove valid as the arches became clogged with silt and other debris (Drolet et al., 2012).

Additional problems stemmed from the inefficiency of the gravity system and the gate valves

installed at the outfalls. The gravity system design failed to effectually convey stormwater to the

Cooper and Ashley Rivers, especially during periods of high tide (O’Connell, 2013). Generally,

gravity networks are difficult to implement on the Charleston peninsula because even moderate

slopes will position the infrastructure at or below tidal zones, thus rendering the system useless

(Drolet et al., 2012). In fact, “areas which can be protected by gravity flow require much larger

diameter conduits than would be required for more steeply sloping areas” (Davis & Floyd, Inc.,

1984). Furthermore, faulty gate valves positioned at the outfalls of the system contributed to

clogging because they created a bottleneck of stormwater and debris (O’Connell, 2013).

Specifically, valves modify the conveyance of hydraulic fluids by increasing, decreasing, or

stopping the flow of substances (Tooling U-SME, 2013; Plastomatic Valves, Inc., 2013).

Compared to other valves, the gate valve is unique because it is composed of a plate-like

obstruction that can be lifted or lowered to control the movement of fluid through a pipeline


(Tooling U-SME, 2013). In this case, the gate valves were installed to prevent backflow from the

Cooper and Ashley Rivers from entering the gravity system; however, when large amounts of

debris and sediment prevented the valves from closing properly, the brick arches became useless

as a drainage system. Ultimately, the brick arches did not prove sufficient as a water conveyance

system for the City of Charleston.

Sanitation System Improvements and the Plum Island Wastewater Treatment Plant

Following this design failure, engineers divided the Charleston peninsula into 13

collection basins that transferred sewage directly to the Charleston Harbor (Drolet et al., 2012-a).

The outfalls of the gravity lines that conveyed water from the basins to the harbor did not prove

efficient during periods of high tide (Drolet et al., 2012-a). To counter this problem, Charleston

Water System, [CWS], added pump stations to this system in the 1920s (Drolet et al., 2012-a).

The added pressure from the pumps successfully prevented the harbor outfalls from becoming

clogged with debris.

However, negative environmental impacts caused by the release of raw sewage into the

harbor culminated in reduced fish populations, swimming restrictions, and a general public

protest (Drolet et al., 2012). In 1963, the South Carolina state legislature passed the Charleston

Harbor Pollution Law, which required the city to install wastewater treatment systems by 1970

(Charleston Water System, n.d.). Specifically, the term wastewater refers to “any water that has

been adversely affected in quality” (Integrated Engineers, Inc., n.d., p. 1). Wastewater differs

from stormwater in that wastewater requires significantly more treatment before being safely

released into the environment. Thus, CWS began developing methods to improve the quality of

the city’s wastewater (Drolet et al., 2012). From 1968 to 1971, the City of Charleston

constructed a wastewater treatment facility located across the Ashley River and west of the


Charleston peninsula (Charleston Water System, n.d. : Drolet et al., 2012). This facility was

named the Plum Island Wastewater Treatment Plant and is still in operation today. Furthermore,

city officials decided that wastewater conveyance tunnels should be constructed to transport

sewage from urban areas to this treatment facility. As a result, CWS installed the Charleston

Sewer Test Tunnel in 1966, modeling it after the original water tunnels implemented further

inland in 1928 (Drolet et al., 2012). When this test tunnel proved effective, city officials awarded

contracts for the construction of a sewer tunnel collection system that would convey sewage

from urban Charleston to the Plum Island Wastewater Treatment Plant (Charleston Water

System, n.d.). Infrastructure within this system included the Original Cooper River Tunnel, the

Original Ashley River Tunnel, the Original Harbor Tunnel, and the Original West Ashley Tunnel

(Drolet et al., 2012). When engineers completed this network in the early 1970s, it greatly

improved the quality of water released into the Charleston Harbor (Drolet et al., 2012).

Development and Deterioration of the Original Cooper River Tunnel

The Original Cooper River Tunnel significantly influenced the design of the Market

Street Tunnel due to its location along Concord Street. Following the enactment of the

Charleston Harbor Pollution Law in 1963, CWS installed the Cooper River Tunnel in 1969 to

transport sewage from Charleston to the Plum Island Wastewater Treatment Plant (Drolet et al.,

2012; Charleston Water System, n.d.). Like other wastewater tunnels constructed in the 1960s,

the Cooper River Tunnel was modeled after water supply tunnels located north of Charleston.

CWS engineers noted that these older tunnels had remained fully functional without a lining;

thus, they believed that the Cooper River Tunnel needed little, if any, ground support. As far as

structural design, the Cooper River Tunnel was comprised of a Prestressed Concrete Cylinder

Pipe [PCCP] supported by steel ribs and wooden lagging and situated at the bottom of a


horseshoe-shaped excavation within the Cooper Marl (Drolet et al., 2012; Klecan, Horner, &

Robison, n.d.). To clarify, “the Cooper Marl is a . . . homogenous, olive green, highly calcareous,

phosphatic, fossiliferous, clayey sand and silt” composition located 30-60 ft. below ground level

across the Charleston Peninsula (Drolet et al., 2012). In addition, “the Cooper Marl is an

excellent tunneling medium as it exhibits sufficient standup time for erection of initial support

yet it is soft enough to excavate by shovel and air spade if desired” (Drolet et al., 2012). Thus,

CWS engineers did not fill the annular space between the PCCP and the tunnel lining because of

the durable nature of the Cooper Marl and the sound structural integrity of older, unlined tunnels.

However, CWS failed to realize the difference in strength between the Cooper Marl located near

the older tunnels and that which encased the Cooper River Tunnel. The layer more commonly

distributed north of Charleston, and thus near the sites of the water supply tunnels, is classified as

either the Parkers Ferry or Harleyville Formations, whereas the substance found in downtown

Charleston is of the Ashley Formation (Klecan et al., n.d.). Of the three, the Ashley Formation is

the weakest type because it has less compressive strength and less carbonaceous bonding than

the Parkers Ferry and Harleyville Formations (Klecan et al., n.d.). In other words, the Ashley

Formation has had less time to consolidate, or settle, than the Parkers Ferry and Harleyville

Formations, and its geological composition prevents it from being as stable as the latter two

substances. The combination of these two factors resulted in “the strength of the Cooper Marl

[being] lower than the circumferential stresses around the [Cooper River Tunnel]. Consequently,

many sections of [this tunnel] became “overstressed.” The tunnel sidewalls . . . failed initially in

compression, and without adequate support the zone of failure quickly extended upwards over

the tunnel” (Klecan et al., n.d.). To clarify, the ground surrounding the tunnel excavation area

was too weak to remain standing without additional ground support. As the walls grew weaker,


sections of the top of the tunnel began to fall and damage the PCCP, thus rendering the tunnel

useless as a water conveyance mechanism. Furthermore, the void between the PCCP and the ribs

and lagging allowed hydrogen sulfide gas to accumulate and to corrode the PCCP (Drolet et al.,

2012). When holes formed in the PCCP, sewage leaked into the tunnel and caused further

deterioration (Drolet et al., 2012). Hence, when CWS hired commercial divers in the 1990s to

inspect the sewage system servicing the Plum Island Wastewater Treatment Plant, city officials

immediately launched the Emergency Sewer System Replacement Program to repair the Cooper

River Tunnel and other sewage conveyance tunnels. In 2005, CWS finally abandoned the Cooper

River Tunnel in favor of the newly constructed Cooper River Replacement Tunnel (Drolet et al.,

2012).

Emergency Sewer System Replacement Program

In the 1990s, CWS hired commercial divers to inspect the sewer system conveying

wastewater to the Plum Island Wastewater Treatment Plant (Drolet et al., 2012). The divers

found this system in a severe state of disrepair; problems included corrosion, collapsed

supporting structures called ribs, holes in the conveyance pipes within the tunnels, and a

dangerous accumulation of sludge (O’Connell, 2013). Engineers employed by the city feared that

these structural damages could culminate in blockages within the tunnels, thus causing an

overflow in urban sewers and the prevention of wastewater treatment at the Plum Island Plant

(O’Connell, 2013). To avoid such a catastrophe, CWS began a fast-tracked sewer system

replacement program that would assume the functions of the older, damaged tunnel network.

CWS divided this construction project into multiple phases. The initial phase, the Harbor Tunnel,

was completed in 2001, followed by the Ashley Sewer Tunnel in 2006 and the Cooper Sewer

Tunnel in 2008 (O’Connell, 2013). In addition to this new sewer system, an extension tunnel was


implemented within the same year to convey sewage from Daniel Island to the Plum Island Plant

(O’Connell, 2013). Furthermore, construction of the West Ashley Sewer Tunnel began in 2013

and is expected to be completed in 2015 (Charleston Water System, n.d.). The City of

Charleston’s “sewer tunnel replacement program is the single largest infrastructure program in

the utility’s history” (O’Connell, 2013, p. 5). Moreover, this systematic repair and replacement

operation has successfully prevented severe blockages within sewage conveyance tunnels in the

Charleston area and has reduced backflow within local stormwater systems. Thus, sewage

treatment has continued, uninterrupted, at the Plum Island Wastewater Treatment Plant.

1984 Master Drainage and Floodplain Management Plan by Davis & Floyd, Inc.

The next proposal to improve the City of Charleston’s drainage systems was a Master

Plan developed in 1984 by Davis & Floyd, Inc. (O’Connell, 2013). This design divided and

directed Charleston’s stormwater into basins situated around the city (O’Connell, 2013). By

definition, “a drainage basin is an area from which the runoff generated is discharged via one

outfall system” (Davis & Floyd, Inc., 1984, p. 2). Physical characteristics of such basins,

including “topography, land use, type and extent of development, soil and surface cover, and

[other] environmental features,” influence the amount of stormwater runoff from a given area,

and thus the type of drainage systems needed to convey this runoff (Davis & Floyd, Inc., 1984, p.

2). Field surveys of the “Study Area,” or the region bounded by “the corporate limits of the City

of Charleston as of May 1984,” resulted in the proposal of 182 individual drainage basins as part

of the Master Plan (Davis & Floyd, Inc., 1984, p. 2). Each of these basins had a designated

outfall in the Cooper River, the Ashley River, the Stono River, or the James Island Creek (Davis

& Floyd, Inc., 1984). This Study Area was subdivided into four distinct regions: Peninsula, West

Ashley, James Island, and Johns Island (Davis & Floyd, Inc., 1984). In addition, field surveys


provided further information regarding the topography of the Study Area. Surface elevations in

this region range from mean sea level, [MSL], or 0 ft., to 25 ft. above MSL; moreover, surface

slopes generally measure 1% or less, and they tend to slant toward one of the main tributaries,

i.e. the Cooper River, the Stono River, etc. (Davis & Floyd, Inc., 1984). As a result of these flat

slopes, the overland flow velocities within the drainage basins are low, causing stormwater

runoff to accumulate more quickly at specific points along the ground (Davis & Floyd, Inc.,

1984). Hence, the flat surface slopes of the Study Area contribute to flooding on the Charleston

peninsula.

Other environmental features of the Study Area that influenced the design of the

proposed drainage facilities include soil types, historic sites, and tidal wetlands. According to the

field surveys, the Study Area consists mostly of clay and fine sand, both of which are surficial

geology of marine or fluvial origin. Based on the composition of the Study Area, engineers from

Davis & Floyd, Inc. concluded that overland runoff velocities from unpaved areas would be

retarded, a large portion of the area’s rainfall would be absorbed into the ground or into

surrounding vegetation, and the slopes of drainage ditches would suffer erosion unless protected,

or unless the overland flow velocities did not surpass 2-3 ft. per second. Additionally, the City of

Charleston developed the new drainage designs so that they would not harm the existing historic

structures within the Study Area. Engineers took precautions during the excavation and

construction phases of this Master Plan to ensure the preservation of intrinsic infrastructure

above and below ground. However, tidal wetlands proved to be the most significant

environmental feature that influenced the development of the drainage basins. Marshlands within

the Study Area “provide a nursery and source of food for various forms of aquatic life;

[furthermore, they] are located along the Cooper River, Ashley River, Stono River and James


Island Creek” (p. 5). To implement or modify drainage structures in these areas, the City of

Charleston had to obtain a permit from the state. Thus, engineers also took precautions to

maintain the integrity of these marshes as much as possible during the construction phase of the

Master Plan.

Furthermore, engineers employed by the city planned improvements projects based on

the intensity of each community’s need for flood relief (O’ Connell, 2013). This massive project

was subdivided into four phases. In the initial phase, engineers assessed the conditions and

capacities of the existing drainage systems in each community, and they made recommendations

regarding potential improvements to each design (Davis & Floyd, Inc., 1984). These evaluations

were based on each system’s capacity deficiency, repair cost, degree of need for improvement,

and the extent to which the proposed improvements would increase public health and safety

(Davis & Floyd, Inc., 1984). Secondly, the City of Charleston had to obtain financial support to

execute these proposed improvements (Davis & Floyd, Inc., 1984). The third phase entailed the

development of blueprints and specifications for these proposals (Davis & Floyd, Inc., 1984).

Lastly, the planned changes for each community’s flood relief system were implemented (Davis

& Floyd, Inc., 1984). Only stormwater lines measuring 24” or greater in diameter were modified,

as the City of Charleston considered these to be the most significant drainage facilities providing

flood relief for the Study Area (Davis & Floyd, Inc., 1984). Projects that served as components

to this Master Plan include the Calhoun Street East Drainage Improvements Project, the Market

Street Drainage Improvements Project, and the Spring/Fishburne Drainage Project.

Calhoun Street East Drainage Improvements Project

Initiated in 1999, the Calhoun Street East Drainage Improvements Project was the first

stormwater drainage design installed in the Charleston area that included a deep tunnel system,


drop shafts, and a stormwater pump station (Kirk, n.d.-b). The city awarded the contract for this

tunnel to a joint venture between Triad Engineering and Bradshaw Construction Corporation.

This joint venture installed one of the branches of the tunnel network under Calhoun Street and

continued it from Marion Square to Concord Street (Kirk, n.d.-b). Another branch conveyed

stormwater under Meeting Street, from Mary Street to Marion Square. Furthermore, drop shafts

were installed along Meeting and Calhoun streets to transport water from the street surface to the

deep tunnel (Kirk, n.d.-b). The access shaft was the first component to be installed, and it

spanned a diameter of 30 ft.; additionally, the branches of the deep tunnel had diameters of 8-ft.

(Kirk, n.d.-b). To clarify, an access, or working, shaft is “a vertical excavation to gain access to

tunnels or mines from the surface” (Bickel & Kuesel, 1982, p. 2). Generally, tunnel engineers

construct the access shaft first so they can work directly on the infrastructure being installed

underground. The Calhoun Street tunnel system is still in effect today, and it carries urban

stormwater from downtown Charleston to the Concord Pump Station (Kirk, n.d.-b). This pump

station transfers the stormwater directly to Charleston Harbor.

Market Street Drainage Improvements Project

In 1997, Davis & Floyd, Inc. initiated the preparations for the construction of the Market

Street Drainage Improvements Project (O’Connell, 2013). City officials selected a deep tunnel

system, rather than an open-cut excavation, as the design for this project to ensure minimal

surface disruptions in the downtown area. Such disruptions could have included traffic detours,

utility relocations, temporary business closures, equipment vibrations, and potential

infrastructure damages. To clarify, an open-cut excavation is one in which engineers dig

downward from the ground surface throughout the course of the project. Additionally, installed

drop shafts would transport stormwater, rather than sewage, directly from the street to this deep


tunnel. Thus, the proposed tunnel would help to relieve surface flooding by conveying massive

amounts of stormwater from the drop shafts to the Concord Pump Station. However, a lack of

funding prevented the City of Charleston from launching construction of this massive project.

Once financial backing for the project was secured, city officials awarded the contract for the

second phase to Triad Midwest Mole in July 2012 (O’Connell, 2013). The city subdivided the

Market Street Drainage Improvements Project into three phases, called Division I, Division II,

and Division III.

In 2006, the City of Charleston initiated construction of Division I. This phase entailed

the improvement of surface water collection systems along Concord Street, the modification of

the controls of the Concord Pump Station, and the installation of an additional pump at this pump

station (Kirk, n.d.-a). The alterations to the pump station’s controls enabled the facility to accept

more water from the newly installed surface collection systems. Additionally, engineers

implemented a fourth pump to increase the maximum capacity of the facility from 90,000

gallons per minute to 120,000 gallons per minute (City of Charleston, 2012). The purpose of this

large accommodation was to prepare the pump station for a massive inflow of stormwater from

the anticipated Division II drainage system (City of Charleston, 2012).

Division II began in 2012 and involves the installation of a 20 ft. diameter, 140 ft. deep

access shaft at the intersection of Market and Concord streets, the excavation of three 54 in. drop

shafts at the intersections of Market and State streets, Market and Anson streets, and Market and

Church streets, the implementation of an emergency outfall on Concord Street, the construction

of a 9 ft. diameter tunnel under Market Street extending from the access shaft to Church Street,

and the installation of another 9 ft. diameter tunnel under Concord Street spanning from the


access shaft to the Concord Pump Station (City of Charleston, 2012). The City of Charleston

divided Division II of the Market Street Drainage Improvements Project into three sub-phases.

Phases 1-3 : Division II : Market Street Drainage Improvements Project. During

Phase 1, or the Initial Investigation, the Triad-Midwest Mole joint venture measured the

dimensions of the brick arch drainage structure located beneath Market Street (Kirk, n.d.-a). The

purpose of this exploration was to evaluate the stability and the size of the brick arch. Such

information would help the engineers to avoid damaging it during the installation of the drop

shafts along Market Street. Prior to the commencement of Division II, city officials had decided

to preserve the brick arches because of their intrinsic value (O’Connell, 2013). Thus, Triad

Midwest Mole engineers took precautions to avoid destroying these underground artifacts during

the construction phase of Division II.

In Phase 2, called the Pre-Excavation, the joint venture dug out a 30 ft. by 30 ft. by 20 ft.

area of road along Market Street to remove abandoned pipelines from the proposed tunnel site

(Kirk, n.d.-a). The engineers extracted this debris to facilitate the installation of the drop shafts

along Market Street. Following the extraction of all impeding utilities from the site, the joint

venture restored the excavated area to its original condition so that a normal flow of traffic could

resume on Market Street (Kirk, n.d.-a).

Phase 3, referred to as Drilling and Construction, includes the installation of the access

shaft, the drop shafts, the emergency outfall, and the deep tunnel network (Kirk, n.d.-a). The

access and drop shafts are intended to replace the existing brick arches beneath Market and

Concord streets (City of Charleston, 2012). In addition, each of the three drop shafts are covered

with a 3 ft. diameter grate to drain flood water from street surfaces (Kirk, n.d.-a). This

stormwater is transported down the drop shafts to the deep tunnel system, from the deep tunnel


to the Concord Pump Station, and finally to Charleston Harbor. Moreover, to construct the deep

tunnel that runs underneath Market and Concord streets, Triad Midwest Mole used a method

called open-faced drilling, or open-faced tunneling. Simply stated, open-faced drilling means that

the face of the TBM is exposed to the dirt excavated during operation. Furthermore, another

significant portion of this project is the emergency outfall, an extra drainage pipeline attached to

the access shaft to prevent the tunnel system from becoming blocked if the Concord Pump

Station ceases to work (Davis & Floyd, Inc., 2012-a). Because this pump station is powered

electrically, the pumps are liable to stop functioning during tropical storms and hurricanes. In

such cases, the fluid movement within the Market Street Tunnel would halt, and the water level

would continue to rise within the system as city streets became inundated. Therefore, the design

by Davis & Floyd, Inc. required Triad Midwest Mole to place the emergency outfall 15 ft.

underground to ensure a downward movement of water from the city streets at all times (Davis &

Floyd, Inc., 2012-a). This outfall is 54 in. in diameter, and its terminal opening is in Charleston

Harbor (Davis & Floyd, Inc., 2012-a). Additionally, a Tideflex valve installed at the terminal exit

prevents an influx of seawater from compromising the outfall’s drainage efficiency (Davis &

Floyd, Inc., 2012-a). Specifically, a Tideflex valve is specialized for pipeline outfall and manhole

installations because it allows water to flow in a singular direction (Tideflex, n.d.). Thus, water is

able to flow out of the emergency outfall, but not into it. Although the emergency outfall makes

the Market Street Tunnel a nearly foolproof drainage design, a combination of circumstances

could still prevent fluid movement from the city streets to the harbor. Collectively, a hurricane or

other major flooding event, a malfunction or power-outage at the Concord Pump Station, and a

high tide preventing water from leaving the emergency outfall could invalidate the drainage

efficiency of the Market Street Tunnel and thus augment urban flooding. Aside from these


extreme conditions, the Market Street Drainage Improvements Project is equipped to

significantly decrease the amount of flooding along Market and Concord streets in downtown

Charleston.

Division III : Spring/Fishburne Drainage Project

In 1968, a six-lane expressway known as the Septima Clark Parkway, or the

“Crosstown,” was constructed as part of U.S. Highway 17 to connect the Ashley River bridges to

the Cooper River bridges (Cabiness et al., 2012). However, the asphalt surface of this highway

created additional stormwater runoff that could not be properly drained by the existing,

undersized system (Cabiness et al., 2012). Consequently, heavy rainfall creates bodies of

standing water that render the Crosstown impassable to vehicles, oftentimes for several hours;

therefore, the inadequate drainage system used to remove surface water from the Septima Clark

Parkway contributes to heavy urban flooding that, in turn, prevents citizens from reaching vital

entities including the Medical University of South Carolina, [MUSC], Roper Hospital, the

Citadel, the City of Charleston police department, the City of Charleston fire department,

schools, churches, businesses, and neighborhoods (Cabiness et al., 2012). As a result, a

component of the 1984 Master Drainage and Floodplain Management Plan by Davis & Floyd,

Inc. is the US17 Septima Clark Parkway Transportation Infrastructure Reinvestment Project, also

known as the Spring/Fishburne Drainage Project (Davis & Floyd, Inc., 1984). The purpose of

this project is to alleviate flooding on the Crosstown and to ensure vehicular mobility on this

highway at all times, regardless of environmental conditions. The area directly affected by this

project comprises 20% of the Charleston peninsula, including commercial and residential areas

(Cabiness et al., 2012). In addition, the Spring/Fishburne design consists of five major parts: the

installation of new, improved surface collection systems in drainage basins within the project


area, the drilling of several drainage shafts from the surface, the boring of 12 ft. diameter

stormwater tunnels that will connect to the afore-mentioned shafts, the implementation of a

pump station along the Ashley River, and the construction of a 550 ft. outfall from this new

pump station to the river itself (Cabiness et al., 2012). Moreover, the design of the

Spring/Fishburne Drainage Project will merit sustainable solutions for travelers using the

Septima Clark Parkway. First, and most importantly, this drainage system will reduce surface

flooding along the highway, thus enabling safer mobility for vehicles and pedestrians alike.

Secondly, an adequate stormwater drainage system will prevent the dilution of saltwater bodies

within the project area (Cabiness et al., 2012). Saltwater bodies require a certain quantity of

brackish water in order to maintain an equilibrium with the surrounding environment; plants and

animals that live in or near saline waters rely on a specific concentration of brackish water to

survive. The Spring/Fishburne Drainage Project would prevent substantial amounts of freshwater

runoff from flooding tidal flats and diluting the salt concentration of brackish tributaries

(Cabiness et al., 2012). Thirdly, an improved drainage system will enhance the quality of the

stormwater being released into the Ashley River because the more quickly runoff is drained from

the highway, the less time is available for it to become stagnant and polluted (Cabiness et al.,

2012). Additionally, a desiltation chamber and a screening mechanism will be installed in the

new pump station to remove debris from the runoff before it is released into the Ashley River

(Cabiness et al., 2012). The desiltation chamber will cleanse the water of silt, sand, and other

unwanted sediments; the screening mechanism will catch debris larger than 2 in. (Cabiness et al.,

2012). Finally, the Spring/Fishburne Project will decrease the city’s use of fossil fuels by

improving traffic mobility on the Crosstown; in other words, an increased efficiency of vehicular

transportation will help eliminate idling motorists on this highway, thus reducing fuel


consumption as well as the emission of greenhouse gasses (Cabiness et al., 2012). Clearly, the

drainage design of the Spring/Fishburne Project will prove beneficial to the environment, to

motorists, and to pedestrians traveling on the Septima Clark Parkway. The City of Charleston has

yet to award the contract for the tunnels and shafts division of this project.


Change Order for the Design of the Market Street Tunnel

As aforementioned, the general design for the Market Street Drainage Improvements

Project is a deep tunnel system connected to three drop shafts, an emergency outfall, and the

Concord Pump Station. Following Triad Midwest Mole’s acceptance of the contract for Division

II, the joint-venture hired a subcontractor, Terracon Consultants, Inc., to gain more information

regarding the current condition of an abandoned tunnel along Concord Street (Terracon

Consultants, Inc., 2012). Installed by CWS in 1969 as the Original Cooper River Tunnel, this

deserted infrastructure was part of the initial wastewater tunnel collection system that conveyed

sewage from Charleston to the Plum Island Wastewater Treatment Plant (Drolet et al., 2012-a).

Furthermore, Terracon Consultants, Inc. utilized a Piezocone Penetration Test [CPTu] to gather

data regarding this tunnel (Terracon Consultants, Inc., 2012). Typically, geotechnical engineers

use CPTu’s to determine the quality and stratigraphy of soil (Zebra Environmental, 2012). The

basic components of the CPTu used by Terracon Consultants, Inc., consist of a probe encased in

a cone that is hydraulically pushed through the ground (Davis & Floyd, Inc., 2012-b). As the

cone is forced through the soil at a steady rate of 2 cm per second, “measurements of tip and side

resistance and porewater pressure” are stored on a portable computer (Davis & Floyd, Inc., 2012-

b, p. 3). Terracon Consultants, Inc. used the CPTu to survey the intersection of Concord and

Market streets, the length of Concord Street, and the area surrounding the Concord Pump Station

(Terracon Consultants, Inc., 2012). Based on the collected data, Terracon observed that two of

their cones “intercepted the tunnel shallower than the design depth of 100 feet” and that this

discrepancy “may be associated with a past collapse of the tunnel” (Terracon Consultants, Inc.,

2012). Additionally, Terracon concluded that the Cooper River Tunnel “could be located in close

proximity (laterally) to the new drainage tunnel which may impact tunnel design and/or its


alignment” (Terracon Consultants, Inc., 2012). To avoid constructing the Market Street Tunnel

too close to the deteriorated Cooper River Tunnel, Triad Midwest Mole submitted a change order

to the City of Charleston in October 2012 that proposed several significant alterations to the

structural design of the tunnel. Among other changes, Triad-Midwest Mole proposed “to lower

the elevation of the drainage tunnel; [to] change its slope to maximize its separation from the

identified void; and [to] realign its connection to the [Concord] Street Pump Station to lower the

new tunnel connection cost” (M. Horton, personal communication, January 29, 2013, p. 1). City

officials approved this change order on February 25, 2013. Furthermore, the researcher has

classified the following alterations as significant to the Market Street Drainage Improvements

Project because each of them was included within this change order.

Increased Depth of the Market Street Tunnel

One of the most significant alterations included within the change order was a drastic

increase in the depth of the Market Street Tunnel and the connecting drop shafts. According to

the original blueprints, Davis & Floyd, Inc. designed the access shaft to be 30 ft. in diameter and

to connect to the tunnel at a depth of 80 ft. (Davis & Floyd, Inc., 2008-c). The drainage tunnel

would then have sloped down to a terminating depth of 138 ft., at which point it would have

connected to the existing Calhoun Tunnel (Davis & Floyd, Inc., 2008-c). The water conveyed by

these joined tunnels would have been transported directly to the Concord Pump Station (Davis &

Floyd, Inc., 2008-c). However, the geotechnical report submitted by Terracon Consultants, Inc.

caused Triad Midwest Mole to question the safety of constructing their new tunnel beside the

Original Cooper River Tunnel. In fact, Terracon’s data and the original drawings for the project

indicated that the Market Street Tunnel would have nearly intersected the Cooper River Tunnel

at a depth of 100 ft. (Davis & Floyd, Inc., 2008-c : Terracon Consultants, Inc., 2012).


Furthermore, Terracon reported that the Cooper River Tunnel “appears to deviate from the

documented location” at this depth (Terracon Consultants, Inc., 2012). Although Terracon

offered an estimated 9 ft. buffer zone between the two tunnels, their experts could not provide an

accurate measurement of the width of this area because they could not pinpoint the exact location

of the Cooper River Tunnel (Terracon Consultants, Inc., 2012). In addition, Triad Midwest Mole

was concerned about the implications of excavating their tunnel in close proximity to dilapidated

infrastructure. Because sections of the top of the Cooper River Tunnel had collapsed, it was

possible that water from the Atlantic Ocean could seep into this tunnel, through the buffer zone,

and then into the Market Street Tunnel during the latter’s excavation (M. J. Kassouf, personal

communication, July 22, 2014). This potential complication would be irreparable, and it would

result in the complete destruction of the Market Street Tunnel (M. J. Kassouf, personal

communication, July 22, 2014). More importantly, the water would destroy the TBM or, worse,

drown workers unable to escape from an impromptu collapse (M. J. Kassouf, personal

communication, July 22, 2014).

To circumvent these hazards, Triad Midwest Mole included a proposal for changing the

dimensions of the Market Street Tunnel and the connecting shafts in their change order. The joint

venture suggested a terminal depth of 140 ft. and a decreased diameter of 20 ft. for the access

shaft (Triad Midwest Mole Joint Venture, 2012). Although Triad Midwest Mole was capable of

constructing an access shaft with a 30 ft. diameter, their engineers felt that the larger size was not

necessary (M.J. Firestone, personal communication, July 30, 2014). Moreover, the original 54 in.

diameter of the drop shafts remained the same, but their final depth was extended from 80 ft. to

140 ft. so as to maintain their connection to the lowered drainage tunnel (P.J. Kassouf, personal

communication, July 23, 2014). By increasing the depth of these shafts, Triad Midwest Mole


lowered the elevation of the drainage tunnel and thus provided for a substantially larger buffer

zone of 40 ft. between the Cooper River Tunnel and the Market Street Tunnel (Terracon

Consultants, Inc., 2012). The joint venture’s engineers felt that this buffer zone would more than

protect the structural integrity of the Market Street Tunnel during Phase 3 of Division II (P. J.

Kassouf, personal communication, July 31, 2014).

To construct the access shaft, Triad Midwest Mole modeled their installation procedure

after a method that Triad had used successfully in 1999 to build the Calhoun Street East

Drainage Improvements Project (Triad Midwest Mole Joint Venture, 2012-b). First, the joint

venture created a shaft footprint by leveling the area around the future access shaft so as to

remove debris from the ground surface (Triad Midwest Mole Joint Venture, 2012-b). Next, the

engineers laid a 6 in. layer of #57 stone along the top of the footprint to serve as a base for a

subsequent 4 in. layer of concrete, referred to as sacrificial concrete leveling (Triad Midwest

Mole Joint Venture, 2012-b). To clarify, #57 stone is a commonly used construction aggregate

that is typically ¾ in. in size and is composed of various types of crushed rock, including

limestone, traprock, washed gravel, granite, argillite, and quartzite (Braen, 2013). The stone and

concrete layers served as a foundation on which the engineers built a caisson shaft cutting shoe, a

20 ft. diameter steel ring that was later attached to the bottom of a caisson shaft to ease its

descent through the ground (Triad Midwest Mole Joint Venture, 2012-b). Specifically, a caisson

is “a shaft of concrete or steel which can be sunk through the ground by excavating the ground

within the perimeter of the lower edge, with the rate of sinking frequently controlled by

compressed air” (Proctor & White, 1977, p. 245). Commonly known as the sinking caisson

method, this construction strategy enabled the joint venture to avoid compromising the ground

stability of the excavation area. Then, the engineers constructed steel forms with which to pour


concrete for the initial 4 ft. of the caisson shaft (Triad Midwest Mole Joint Venture, 2012-b).

Furthermore, the engineers poured the concrete around a set of rebar, or steel bars, so as to

reinforce the strength of this shaft. The engineers arranged the rebar so that steel hoops encircled

standing bars; additionally, the hoops were spaced one vertical foot apart from each other, and

the bars were spaced one horizontal foot apart from each other. The rebar was located 18” from

the inside wall of the access shaft. Moreover, the wet concrete was allowed to set until it reached

a strength of 1000 pounds per square inch [psi] (Triad Midwest Mole Joint Venture, 2012-b).

Engineers slowly sunk this caisson, which was 4 ft. in length, 20 ft. in diameter, and 18 in. thick,

by excavating the ground on the inside of the structure using a Caterpillar 302.5C Mini

Hydraulic Excavator (Caterpillar, 2007 : P. J. Kassouf, personal communication, February 10,

2015). Any excess ground water that rose within the caisson was removed with a Grindex

electrical submersible drainage pump and a Godwin sub-prime electric submersible pump and

deposited into a sanitary manhole on site (Grindex, n.d. : Godwin Pumps, n.d. : Triad Midwest

Mole Joint Venture, 2012-b). When the caisson was submerged 4 ft. into the ground, the

engineers assembled the steel forms for the next segment of the shaft and repeated the process of

pouring and sinking the caissons until the entire access shaft was completed (Triad Midwest

Mole Joint Venture, 2012-b). Additionally, the engineers allowed 6 ft. of the rebar within each

segment to remain exposed above ground so as to ease the process of connecting the shaft pieces.

After installing one portion of the shaft, the engineers used rebar tying wire manufactured by

Concreate Welded Wire Reinforcing Co. to connect the 6 ft. of free rebar to the rebar of the next

segment; thus, the engineers ensured the structural integrity of the entire caisson by

implementing rebar within the walls of the shaft (Concreate Welded Wire Reinforcing Co., n.d. :

P. J. Kassouf, personal communication, February 10, 2015).


Furthermore, the concrete segments following the initial 4 ft. caisson measured 14 ft. in

length and 20.3 ft. in diameter; moreover, the additional 4 in. width of these pieces allowed for

the strategic installment of 1 in. steel piping along the access shaft wall (Triad Midwest Mole

Joint Venture, 2012-b). This piping provided a medium through which the engineers could pump

slurry, a mixture of bentonite and water, into the annular space between the access shaft wall and

the ground. Engineers used a FM13V model Ditch Witch slurry pump for this purpose (Ditch

Witch, n.d. : P. J. Kassouf, personal communication, February 10, 2015). Moreover, bentonite is

defined as “a naturally occurring clay” that “has a large capacity for absorbing water. In

suspension, it is a liquid when agitated, and a gel if left to stand. The liquid suspension can be

injected into a permeable soil mass and allowed to congeal in the voids, thereby decreasing

permeability” (Bickel & Kuesel, 1982, p. 218). In other words, Triad Midwest Mole engineers

pumped slurry into the annular space between the access shaft wall and the surrounding soil so as

to keep the water pressure around the shaft consistent with that of the ground water table, or, in

this case, with sea level (Bickel & Kuesel, 1982). Maintaining the equilibrium of the water table

allowed the engineers to further ensure the ground stability of the excavation area.

After Triad Midwest Mole constructed the first 85 ft. of the access shaft, engineers

installed a concrete bearing pad to prevent this top section of the caisson from sinking (Triad

Midwest Mole Joint Venture, 2013-a). This circular bearing pad was 2 ft. thick and extended 4 ft.

7 in. from the inside of the access shaft wall (Triad Midwest Mole Joint Venture, 2013-a). To

implement this structure, engineers used air spades to hand-mine the Cooper Marl surrounding

the caisson shaft before pouring any concrete. To clarify, both the clay spades and the #95LA3

model air diggers comprising the air spades were manufactured by Ingersoll-Rand (Ingersoll

Rand, 2015-a, 2015-b : P. J. Kassouf, personal communication, February 10, 2015).


Furthermore, the engineers mined one fourth of the bearing pad at a time to ensure the security of

the initial 85 ft. of the access shaft. Therefore, at least three fourths of the shaft bottom was

supported by stable ground at any given time during the excavation of the bearing pad (M. J.

Kassouf, personal communication, December 31, 2014). Due to the stability of the Cooper Marl,

the engineers did not need to use forms when pouring concrete for the bearing pad (P. J. Kassouf,

personal communication, February 10, 2015). Following the construction of the bearing pad, the

engineers continued to mine the access shaft until it reached its terminal depth of 140 ft.

However, Triad Midwest Mole chose to support the 15 ft. of caisson between the bearing pad

and the bottom of the access shaft with liner plates and steel ribs rather than with concrete and

rebar (Triad Midwest Mole Joint Venture, 2012-b). These standard liner plates with corrugations

were manufactured by DSI Underground Systems Inc. (DSI Underground Systems Inc., n.d. : P.

J. Kassouf, personal communication, February 10, 2015). Had the engineers chosen to line the

final 15 ft. of the access shaft with concrete and rebar before the end of the project, they would

have had to mine through these materials to adjust the tunnel headings for the Market Street and

Concord Street sections of the tunnel (M. J. Kassouf, personal communication, December 31,

2014 : P. J. Kassouf, personal communication, February 10, 2015). Thus, the engineers chose to

use liner plates as temporary support for this section of the shaft so as to increase project

efficiency (M. J. Kassouf, personal communication, December 31, 2014 : P. J. Kassouf, personal

communication, February 10, 2015). Although installing steel ribs complicated the readjustment

of the Market Street and Concord Street tunnel headings, Triad Midwest Mole’s design engineer,

Arup Texas Inc., required the joint venture to use them (P. J. Kassouf, personal communication,

February 10, 2015).


Subsequently, the engineers used a Putzmeister 20Z-Meter Truck-Mounted Concrete

Boom Pump to fill the annular space surrounding the caisson shaft with grout (Putzmeister

America, Inc., 2013 : P. J. Kassouf, personal communication, February 10, 2015). Again, the 1

in. steel piping surrounding the caisson shaft served as a medium through which the engineers

could pump fluids. As the grout gradually filled the space between the access shaft and the

ground, the engineers deposited the displaced slurry into a separate tank (Triad Midwest Mole

Joint Venture, 2012-b). Later, the engineers loaded the slurry onto a slurry tanker and hauled it

away from the site (Triad Midwest Mole Joint Venture, 2012-b).

Additionally, the engineers constructed three drop shafts along Market Street that

connected to the deep tunnel system at a depth of 130 ft. (Triad Midwest Mole Joint Venture,

2012-b). To successfully execute this phase, the engineers constructed a steel work deck over the

top of each drop shaft location to serve as a platform for the workers and a bearing pad for each

section of shaft casing (Triad Midwest Mole Joint Venture, 2013-b). This platform included a

hole in the center through which the engineers could lower sections of the casing into the ground

with a crane (Triad Midwest Mole Joint Venture, 2013-b). Furthermore, the drop shaft

installation procedure was divided into a drilling operation and a casing operation (Triad

Midwest Mole Joint Venture, 2013-b). During the initial stage, engineers used an AF 220

Hydraulic Drill Rig to spin a 70 in. diameter, 50 ft. long steel casing into the Cooper Marl to

serve as a protective outer shell for the interior of the drop shaft (Triad Midwest Mole Joint

Venture, 2013-b : IMT International, n.d.). The engineers implemented this casing by drilling 25

ft. of a 30 ft. long segment into the ground (Triad Midwest Mole Joint Venture, 2013-b). Leaving

the last 5 ft. exposed, the engineers used the steel platform to position the next 20 ft. long


segment so they could weld the two pieces together (Triad Midwest Mole Joint Venture, 2013-

b).

During this procedure, the engineers pumped slurry into the drill hole using a FM13V

model Ditch Witch slurry pump to ease the removal of displaced muck from the interior of the

shaft (Ditch Witch, n.d. : Triad Midwest Mole Joint Venture, 2013-b). Next, the engineers

installed a 54 in. diameter, 127 ft. long casing inside each of the 70 in. diameter casings (Triad

Midwest Mole Joint Venture, 2013-b). Moreover, the 70 in. diameter casing only surrounded the

initial 50 ft. of the other shaft because the remaining 77 ft. of the drop shaft was safely secured in

the Cooper Marl (Triad Midwest Mole Joint Venture, 2013-b). The second shaft was divided into

four 30 ft. long sections and one 7 ft. long section, and the engineers used the same installation

procedure to weld them together and to drill them into the ground (Triad Midwest Mole Joint

Venture, 2013-b). Each time a section of the 54 in. diameter shaft was implemented, a small

amount of slurry was displaced from the 70 in. diameter shaft and pumped to a slurry tanker

(Triad Midwest Mole Joint Venture, 2013-b). When the 54 in. diameter shaft was completed, the

remainder of the slurry was pumped to the slurry tanker and removed from the work site (Triad

Midwest Mole Joint Venture, 2013-b). Finally, the engineers filled the annular space between the

70 in. diameter casing and the 54 in. diameter casing with grout (Triad Midwest Mole Joint

Venture, 2013-b).

Decreased Slope of the Market Street Tunnel

According to the original blueprints by Davis & Floyd, Inc., the slope of the tunnel from

the access shaft to the Concord Pump Station was designed to be 2.34%, or decreasing 2.34 ft.

vertically per lateral 100 ft. (Davis & Floyd, Inc., 2008). However, Triad Midwest Mole

engineers objected to this plan because this drastic slope would have compromised the safety of


the workers in the tunnel. To construct the tunnel with this slope, the engineers would have

needed additional equipment and laborers. Specifically, the engineers would have required

hydraulic winches for the muck cars in the tunnel, multiple electrical submersible pumps, and

safety chains on any heavy objects that could have slid down the tunnel during excavation.

To clarify, hydraulic winches are tools that use a hydraulic motor to power spool rotation

by which to pull objects from one place to another (Hydraulic Winches: Hydraulic Winch, n.d.).

Because the engineers used railway cars to transport muck from the TBM to the access shaft, a

2.34% slope would have required the use of hydraulic winches so as to haul the cars through the

tunnel (P. J. Kassouf, personal communication, January 10, 2015). In fact, the joint venture

would have needed to use a minimum of two hydraulic winches within the tunnel to ensure the

safety of the laborers during excavation (P. J. Kassouf, personal communication, January 10,

2015). If one hydraulic winch broke while the TBM was in operation, the other would prevent

the railway cars from rolling backwards and crushing workers inside the tunnel (P. J. Kassouf,

personal communication, January 10, 2015). Furthermore, Triad Midwest Mole engineers would

have purchased TYS-32 Winch Misc M2030 model hydraulic winches from Markey Machinery

for this purpose (P. J. Kassouf, personal communication, January 10, 2015 : Markey Machinery,

n.d.).

In addition, a 2.34% slope would have created a significant flow of ground water from

the location of the access shaft to the lowest point of the tunnel. This fluid, coupled with the

slippery texture of the Cooper Marl, would have proven hazardous for workers walking through

the tunnel. Moreover, ground water contact with the TBM would have permanently damaged this

machinery. Therefore, the engineers would have needed to install several electrical submersible

pumps to transport ground water from the lowest point of the tunnel to the ground surface. Had


they constructed the tunnel with a 2.34% grade, the engineers would have employed two No:

PD605181-INT model Electrical Submersible Drainage pumps by Grindex during excavation (P.

J. Kassouf, personal communication, January 10, 2015 : Grindex, n.d.). One pump would have

been positioned near the TBM to transport water to the bottom of the access shaft (M. J. Kassouf,

personal communication, December 31, 2014). Then, the other pump would have moved the

water from the bottom of the access shaft to the ground surface (M. J. Kassouf, personal

communication, December 31, 2014). This hypothetical procedure does not differ greatly from

the actual ground water control method used during the installation of the tunnel; in fact, the only

discrepancy is that the engineers used a GSP/05/10/20 Sub-Prime Electric Submersible model

Godwin pump near the TBM instead (P. J. Kassouf, personal communication, January 10, 2015 :

Godwin Pumps, n.d.).

Lastly, the engineers would have needed heavy cables to secure any large objects that

could have slid down the length of the 2.34% grade tunnel. Specifically, Triad-Midwest Mole

would have employed the use of 2” Extra Improved Plow Steel, Right Regular Lay model cables

manufactured by Web Rigging Supply to secure heavy machinery (P. J. Kassouf, personal

communication, January 10, 2015 : Web Rigging Supply, n.d.). Moreover, additional project

costs would have resulted from a need for more laborers and excavation time. To implement a

tunnel with a 2.34% slope, the joint venture would have needed to hire at least four more

workers to operate the hydraulic winches and to monitor the integrity of the cables connecting

these devices to the railway cars (P. J. Kassouf, personal communication, January 10, 2015).

Furthermore, construction of said tunnel would have required an extra four months of mining,

thus increasing the overall cost of the project (P. J. Kassouf, personal communication, February


7, 2015). Ultimately, the joint venture chose to modify the proposed 2.34% grade of the tunnel to

0.082% to avoid worker fatalities and to increase project efficiency (Arup, 2013).

Connection to Concord Street Pump Station vs. Calhoun Street Tunnel

In the original blueprints for the Market Street Drainage Improvements Project, Davis &

Floyd, Inc. designed the Concord Street Tunnel to connect to the existing Calhoun Street Tunnel

(Davis & Floyd, Inc., 2008-a). From this junction, the water transported by both tunnels would

have been delivered to the Concord Street Pump Station and, ultimately, to Charleston Harbor.

However, Triad Midwest Mole raised several concerns regarding this proposed connection. First,

the Calhoun Street Tunnel has an 8 ft. diameter, whereas the Concord Street Tunnel, as depicted

in the initial drawings, would have had a 10 ft. diameter; therefore, Triad Midwest Mole would

have needed to disassemble a section of the Calhoun Street Tunnel to connect it to the Concord

Street Tunnel (Davis & Floyd, Inc., 2008-a). Secondly, Davis & Floyd, Inc. designed this

juncture to measure 90 degrees and to gradually decrease the diameter of the Concord Street

Tunnel from 10 ft. to 6 ft. at this point (Davis & Floyd, Inc., 2008-a). Even though the portion of

the Concord Street Tunnel adjoined to the Calhoun Street Tunnel would have measured less than

8 ft., Triad Midwest Mole was still concerned that this connection would destroy the Calhoun

Street Tunnel. Thirdly, the 90 degree juncture between the tunnels would have created an

imbalance of water pressure inside the Calhoun Street Tunnel (P. J. Kassouf, personal

communication, January 17, 2015). According to the blueprints by Davis & Floyd, Inc., the

portion of the Concord Street Tunnel connecting to the Calhoun Street Tunnel would have

occupied half of the top of the latter infrastructure; therefore, the water pressure would have

increased on that side of the tunnel only, causing cracks and an eventual collapse of the Calhoun

Street Tunnel (Davis & Floyd, Inc., 2008-a). To avoid destroying the Calhoun Street Tunnel,

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CCoQFjAB&url=http%3A%2F%2Fwww.minimallyminimal.com%2Fblog%2F90degrees&ei=CxtpVOCYCcSqNoC4gJgI&usg=AFQjCNEP_2whCPFx6JsqFt1xWOTxAK6WYg&sig2=SMyOsGUQOA3bQfKgR14SFw&bvm=bv.79142246,d.eXY


Triad Midwest Mole proposed to excavate the Concord Street Tunnel in the shape of an S-curve

and to connect this infrastructure directly to an existing wet-well, or water containment vault, of

the Concord Pump Station (Triad Midwest Mole Joint Venture, 2012-a : Triad Midwest Mole

Joint Venture, 2012-b). Hence, the S-curve design enabled the engineers to preserve the Calhoun

Street Tunnel and to provide the Market Street Tunnel system with an outlet to Charleston

Harbor.

Final Lining of the Market Street Tunnel

In the original blueprints for the Market Street Tunnel, Davis & Floyd, Inc. provided for

the use of interlocking rebar and cast-in-place concrete as the final lining for the tunnel. The

rebar design would have resembled that used by Triad Midwest Mole during the construction of

the access shaft, with steel rods running laterally along the sides of the tunnel, periodically

interrupted by intersecting steel hoops (Davis & Floyd Inc., 2008-b : P. J. Kassouf, personal

communication, January 17, 2015). Moreover, the installation of the cast-in-place concrete

would have been similar to the procedure used by Triad Midwest Mole to construct the access

shaft caissons. Engineers would have placed steel forms along sections of unlined tunnel and

filled the forms with concrete. Once the concrete reached a specified strength, engineers would

have removed the forms from the tunnel, thus encasing the rebar in an impenetrable layer of

hardened concrete (Davis & Floyd Inc., 2008-b : P. J. Kassouf, personal communication, January

17, 2015). However, due to the stability of the Cooper Marl, Triad Midwest Mole felt that the

interlocking rebar would not be necessary to maintain the structural integrity of the tunnel (M. J.

Kassouf, personal communication, December 31, 2014). Thus, joint venture engineers elected to

use a cast-in-place concrete mix manufactured by Ready Mixed Concrete Company (M. J.

Kassouf, personal communication, December 31, 2014 : Ready Mixed Concrete Company,


2013). Furthermore, this mix included fibrillated polypropylene fibers that reinforced the

strength of the concrete (Ready Mixed Concrete Company, 2013). When incorporated at 1.5

pounds of fibers per cubic yard of concrete, the polypropylene fibers served as an acceptable

alternative to the interlocking rebar design because they strengthened the concrete mix and

ensured the integrity of the tunnel liner (BASF Construction Chemicals, LLC, 2008). While not

as strong as the rebar, Triad Midwest Mole engineers believed that the fibers would sufficiently

reinforce the tunnel liner. Therefore, the joint venture included a request to use polypropylene

fibers instead of rebar in the project change order.

Elimination of Ground Freezing at Junction of Market Street and Calhoun Street Tunnels

The initial project designs by Davis & Floyd, Inc. include the use of ground freezing to

stabilize the soil around the junction between the Concord Street Tunnel and the Calhoun Street

Tunnel. To clarify, ground freezing involves “[converting] pore water into ice by the continuous

circulation of a cryogenic fluid within a system of small diameter, closed-end pipes installed in a

pattern consistent with the shape of the area to be treated” (Moretrench, n.d., p. 1). These pipes

are installed vertically in the ground and connected in a series-parallel formation (Moretrench,

n.d.). Furthermore, “the frozen pore water acts as a bonding agent, fusing together particles of

soil or rock to significantly increase compressive strength and impart impermeability”

(Moretrench, n.d., p. 1). Ground freezing can be executed in any type of soil and in permeable or

fissured rock; moreover, this procedure is most cost efficient “in difficult, disturbed or sensitive

ground” (Moretrench, n.d., p. 2). Additional conditions that merit ground freezing as a cost

effective method for achieving ground stabilization include “ground where penetrability drilling,

jet grouting, clamshell excavation, or other vertical cut-off tools is limited,” “filled ground and

ground containing man-made obstructions,” “virgin ground containing cobbles, boulders, or an


irregular soil [or] rock interface,” and “ground that has been disturbed due to unstable conditions

or water inflow” (Moretrench, n.d., p. 1).

Had Triad Midwest Mole followed Davis & Floyd, Inc.’s plans, they would have used

brine as a cooling agent to freeze the ground water around the tunnels’ junction (P. J. Kassouf,

personal communication, January 17, 2015). In fact, “chilled calcium chloride brine is the most

commonly used cooling agent” for ground freezing procedures because it is practical for long-

term freezing periods that may range from several weeks to several months (Moretrench, n.d., p.

2). To install chilled calcium chloride brine, engineers pump the substance down a drop tube to

the bottom of a freeze pipe and allow it to travel through a series-parallel formation of other

freeze pipes until it returns to a refrigeration plant to be chilled and recirculated (Moretrench,

n.d.). As the brine is pumped from the ground surface to the bottom of a freeze pipe, it withdraws

heat from the surrounding soil and thus solidifies the ground (Moretrench, n.d.). Provided that

engineers install the freeze pipes correctly, brine freezing cools the ground in a consistent, even

manner. When the ground has reached a desired stability, engineers use slightly warmer brine to

maintain the extent of the ground freezing present (Moretrench, n.d.). Furthermore, brine

freezing is typically applied during the construction of shafts, large, circular, open excavations,

horizontal tunnels, and tunnel crown supports (Moretrench, n.d.).

Triad Midwest Mole expostulated connecting the Concord Street Tunnel to the existing

Calhoun Street Tunnel because this jointure would have destroyed the Calhoun Street Tunnel.

However, the City of Charleston’s approval of the change order allowed Triad Midwest Mole to

connect the Concord Street Tunnel to a wet-well in the Concord Pump Station instead. Thus, the

change order removed the need for ground freezing during the course of the project.

Furthermore, had the change order not been approved, Triad Midwest Mole would have objected


to ground freezing based on their experience with construction in the Cooper Marl. Due to the

marl’s strength, joint venture engineers felt that “the effectiveness of the ground freezing in the

Cooper Marl” was questionable (Triad Midwest Mole Joint Venture, 2012). Ultimately, Triad

Midwest Mole eliminated the use of ground freezing during the course of the Market Street

Drainage Improvements Project due to the approved connection between the Concord Street

Tunnel and the Concord Pump Station and to the stability of the Cooper Marl.


Chapter III: Methods

When Triad Midwest Mole received the contract for Division II of the Market Street

Drainage Improvements Project, they proposed several modifications to facilitate the tunnel

installation process. Furthermore, the governing question for this thesis is: how have the

proposed changes to the original plans for the Market Street Drainage Improvements Project

increased the cost efficiency of this design in terms of the money saved by the City of

Charleston? As aforementioned, the Market Street Tunnel is significant to civil engineers

because it is only the second deep stormwater tunnel system to be installed in Charleston.

Therefore, the results of this thesis satisfy an informational gap in the professional field because

no such cost analysis has been performed for a tunneling project in this area. Therefore, the

researcher has conducted this study to fill a gap in the civil engineering field, as well as to

provide a point of reference for engineers who wish to improve the cost efficiency of tunneling

projects in Charleston.

The methodology for this study involves an inductive analysis of the qualitative and

quantitative data collected by the researcher. The qualitative data is derived from the review of

literature, in which the researcher discusses the engineering techniques used to modify the

original 1997 blueprints. In addition, the quantitative data is the estimated amount of money

saved by the City of Charleston as a result of the alterations made to these plans. The products of

this data analysis are a cost efficiency evaluation of the engineering techniques used to change

the initial construction plans, as well as a cumulative quantity representing the amount of money

saved by the City of Charleston as a result of the project change order.


Materials

The researcher selected population samples from the pool of alterations made to the

original plans for the Market Street Drainage Improvements Project. The researcher chose design

modifications to study based on whether they were included in the project change order.

Specifically, the researcher investigated the increased depth of the tunnel, the decreased slope of

the tunnel, the final lining for the tunnel, the tunnel’s connection to the Concord Pump Station,

and the elimination of ground freezing during the course of the project. To substantiate the cost

analysis of these structural changes, the researcher has used project submittals, tunnel drawings,

equipment quotes and specifications, copies of Triad Midwest Mole’s original bid tab, and letters

of correspondence between Triad Midwest Mole, Black & Veatch Corporation, and Davis &

Floyd, Inc.

Procedures

The researcher followed a chronological procedure to collect and to analyze data. First,

the researcher assembled qualitative data within the review of literature by explaining the

engineering techniques used to modify the original blueprints for the tunnel. The researcher

worked with the mentor and Triad employees to acquire academic sources that supported the

joint venture’s decision to alter the proposed drainage system. Furthermore, the qualitative data

within the review of literature serves as the basis for the presentation and analysis of the

quantitative data included in Chapter IV. Thus, the researcher has used the explanations of the

engineering methods to demonstrate how the alterations to the initial plans affected the cost

efficiency of the Market Street Drainage Improvements Project. Within Chapters IV and V, the

researcher has examined the cost of the modified plans and has compared them to the cost of the

original design. Ultimately, this cost comparison has allowed the researcher to approximate the


amount of money saved by the City of Charleston as a result of the change order proposed by

Triad Midwest Mole.

The researcher’s methods are justified by similar studies conducted in the civil

engineering field. Two such bodies of literature are Benefit—Cost Analysis of Delta Water

Conveyance Tunnels, published by the Eberhardt School of Business, and Underground Unit

Cost Analysis, published by International Linear Collider. The former source discusses a cost

analysis of the design and implementation of a Delta Water deep tunnel conveyance system. This

particular study is relevant to the researcher’s thesis because the Market Street Tunnel is also a

deep tunnel network. Similarly, Underground Unit Cost Analysis examines the cost efficiency of

a construction project that culminated in the installation of a tunnel in Illinois. Although the

project discussed in the latter source is not a deep tunnel, the study is still largely similar to the

procedure outlined in the researcher’s methodology. Hence, the researcher’s strategies are

supported by earlier studies that have been conducted within the civil engineering field.

However, the researcher did not collect qualitative data from either source because neither can be

used to defend the engineering techniques involved with the construction of the Market Street

Tunnel. Moreover, the unique geology and geography of the Charleston area prevent the

researcher from comparing the Market Street Drainage Improvements Project to any other

tunneling excavation outside of downtown Charleston. Therefore, the researcher has relied on

tunnel drawings and design specifications to uphold the methods used by Triad Midwest Mole in

installing the Market Street Tunnel.

The researcher has analyzed the quantitative data presented in Chapter IV using

arithmetic and tables. Moreover, these results have been discussed thoroughly in Chapter V in

terms of how they affected the cost efficiency of the Market Street Drainage Improvements


Project. Furthermore, the most important points of the quantitative data will be displayed in a

powerpoint presentation during the researcher’s oral defense.

Evaluation

The accuracy of the qualitative and quantitative data will be determined by the mentor, as

he is an expert on the topic of the Market Street Tunnel. Furthermore, the researcher’s study will

be deemed a success if it clearly answers the governing question by explaining how the modified

engineering methods used to construct the Market Street Tunnel affected the cost efficiency of

the project as a whole. Additionally, the study must provide a cumulative estimate of the money

saved by the City of Charleston as a result of these design changes. If the quantitative data

indicates that the project change order did not save the City of Charleston money, the

researcher’s thesis may still be considered successful as long as the researcher answers the

governing question.

Conclusion

The conclusion of the thesis is a cost efficiency evaluation of the engineering techniques

used to modify the original construction plans for the Market Street Tunnel. To confirm the

validity of the data, the researcher has carefully checked the calculations used to determine the

amount of money saved by the City of Charleston as a result of these design alterations. In

addition, the researcher has verified the data’s accuracy with the mentor, who has access to

information regarding the project change order. Due to the inductive nature of this thesis, the

data has solely answered the governing question instead of confirming or rejecting hypotheses

made by the researcher.


Chapter IV

Increased Depth of the Market Street Tunnel

Modified Portion of

the Market Street

Tunnel

Construction

Procedure

Cost Before

Change

Order

Cost After

Change

Order

Cost Before

Change

Order - Cost

After Change

Order

Access Shaft

Standard Preconstruction Procedures to Prepare

for Mining of Concord Street Tunnel

$200,000.00 $280,000.00 -$80,000.00

Standard Preconstruction Procedures to Prepare

for Mining of Market Street Tunnel

$200,000.00 $250,000.00 -$50,000.00

Restoration of Parking Lot, Removal of Wooden Fence and

Gravel

$0.00 $25,000.00 -$25,000.00

Curb Restoration along

Concord Street

$0.00 $25,000.00 -$25,000.00

Demobilize Tunnel Equipment

$100,000.00 $130,000.00 -$30,000.00

Additional Costs for

the Access Shaft Only

Included in the

Change Order

Concrete Lift #6:

Concrete Form, Rebar Tying Wire, Concrete

Pour, and Caisson Sinking

$200,000.00 -$200,000.00


Concrete Lift #7: Concrete Form, Rebar Tying Wire, Concrete


$200,000.00 -$200,000.00



$200,000.00 -$200,000.00



$200,000.00 -$200,000.00

Concrete Lift #10: Concrete Form, Rebar Tying Wire, and

Concrete Pour

$200,000.00 -$200,000.00

Bottom of Access

Shaft: Bearing Pad, Steel Ribs, and Liner Plates

$270,000.00 -$270,000.00

Layer of #57 Stone on Access Shaft Bottom

and Pouring of Concrete Floor Slab

$100,000.00 -$100,000.00

Pour Concrete Wall Connecting Floor Slab

to Bearing Pad

$180,000.00 -$180,000.00

Market Street Tail

Tunnel Excavation

$200,000.00 -$200,000.00

Concord Street Tail Tunnel Excavation

$200,000.00 -$200,000.00

Drop Shafts

Prepare Work Area A:

Intersection of Market Street and State Street

$35,000.00 $50,000.00 -$15,000.00


Drill Drop Shaft A $115,000.00 $244,000.00 -$129,000.00

Demobilize Work Area A

$10,000.00 $20,000.00 -$10,000.00

Asphalt Pavement Restoration Shaft A

$10,000.00 $20,000.00 -$10,000.00

Prepare Work Area B: Intersection of Market Street and Anson

Street

$35,000.00 $50,000.00 -$15,000.00

Drill Drop Shaft B $115,000.00 $244,000.00 -$129,000.00

Demobilize Work Area B

$10,000.00 $20,000.00 -$10,000.00

Asphalt Pavement

Restoration Shaft B

$10,000.00 $20,000.00 -$10,000.00

Prepare Work Area C:

Intersection of Market Street and Church Street

$35,000.00 $50,000.00 -$15,000.00

Drill Drop Shaft C $115,000.00 $244,000.00 -$129,000.00

Demobilize Work

Area C

$10,000.00 $20,000.00 -$10,000.00

Asphalt Pavement Restoration Shaft C

$10,000.00 $20,000.00 -$10,000.00


the Drop Shafts Only

Included in the

Change Order

Mobilization of

Equipment

$120,000.00 -$120,000.00

Tunnels Including

Adits: Market Street

Tunnel

TBM Setup and Launch

$100,050.00 $100,050.00

Installation of Additional TBM

$150,000.00 $190,000.00 -$40,000.00


Attachments and First Railroad Track for First Five-Muck-Car

Train at 32 ft. from Access Shaft Bottom

Installation of

Additional Short Conveyor Belt for

Muck Removal at 140 ft. from Access Shaft Bottom

$200,000.00 $225,000.00 -$25,000.00

*Installation of

Second Railroad Track for the Market

Street Tunnel Eliminated from Construction

Procedures Following Submission and

Approval of Change Order

Installation of Second

Railroad Track for Second Five-Muck-

Car Train at 300 ft. from Access Shaft Bottom

$100,000.00 $125,000.00

Installation of Railroad Track Switch for

Operational Two Train Mining

$0.00 $15,000.00 -$15,000.00

Two Crew Shifts to

Mine from Tunnel Excavation Station 41+00 to Station

45+55 (Davis & Floyd, Inc., 2008-d)

$450,000.00 $480,000.00 -$30,000.00

Two Crew Shifts to

Mine from Tunnel Excavation Station

45+55 to Station 50+11 (Davis & Floyd, Inc., 2008-d)

$450,000.00 $480,000.00 -$30,000.00

Installation of Final

Tunnel Liner from Station 38+00 to

Station 50+00 (Davis & Floyd, Inc., 2008-d)

$600,000.00 $625,000.00 -$25,000.00


Market Street Tunnel

Mining Only

Included in the

TBM Setup and Launch to Mine

Market Street Tail Tunnel

$160,000.00 -$160,000.00


Change Order

Tunnels Including

Adits: Concord Street

Tunnel

Mobilization of AF 220 Hydraulic Drill

Rig for Drilling of Concrete Down Holes

$0.00

TBM Setup and Launch

$175,000.00 $175,000.00

Installation of

Additional TBM Attachments and First

Railroad Track for First Five-Muck-Car Train at 32 ft. from

Access Shaft Bottom

$150,000.00 $190,000.00 -$40,000.00

Installation of Additional Short

Conveyor Belt for Muck Removal at 140

ft. from Access Shaft Bottom

$150,000.00 $190,000.00 -$40,000.00

Installation of Second Railroad Track for

Second Five-Muck-Car Train at 300 ft.

from Access Shaft Bottom

$100,000.00 $125,000.00 -$25,000.00


Concord Street

Tunnel Mining Only

Included in the

Change Order

Mobilization of AF 220 Hydraulic Drill

Rig for Drilling of Concrete Down Holes

$130,000.00 -$130,000.00

Total Cost Before Change Order Total Cost After Change Order Total Savings

$3,635,050 $6,592,000 -$2,956,950

Regarding the installation of the access shaft, “Standard Preconstruction Procedures” for

both the Market Street and Concord Street Tunnels involved the engineers checking the integrity

of the mining equipment, especially the TBM, before beginning the excavation process (P. J.

Kassouf, personal communication, February 22, 2015). Next, the “Floor Slab” is simply the

concrete floor of the access shaft. Thirdly, the “Tail Tunnel” that the engineers excavated was a


small space adjoined to the access shaft that resembled a partially mined tunnel. In total, the

engineers constructed two tail tunnels: one for the Market Street Tunnel and one for the Concord

Street Tunnel. To clarify, the purpose of the tail tunnels was to provide additional room in the

bottom of the access shaft so that the engineers could easily crane lift the muck cars to ground

level, empty them, and return them to the shaft during the mining process (P. J. Kassouf,

personal communication, February 22, 2015). While the cars were being emptied, the locomotive

used to haul them would be parked within the tail tunnel, thus providing the engineers more

room to attach dirt-filled muck cars to the crane cable (P. J. Kassouf, personal communication,

February 22, 2015). Hence, by enlarging the size of the access shaft bottom, the tail tunnels

facilitated the excavation of both the Market Street and Concord Street tunnels.

Concerning the implementation of the drop shafts, “Prepare Work Area” refers to the

engineers’ placement of caution signs and fences around the future construction site of each drop

shaft (P. J. Kassouf, personal communication, February 22, 2015). Moreover, the “Installation of

Additional Short Conveyor Belt” listed under the sections entitled, “Tunnels Including Adits:

Market Street Tunnel,” and “Tunnels Including Adits: Concord Street Tunnel,” indicates the

joint venture’s use of a conveyor belt to transport displaced muck from the TBM to the muck

cars (P. J. Kassouf, personal communication, February 22, 2015). As stated in the table, at 140 ft.

from the bottom of the access shaft, the engineers installed more lengths of conveyor belt in

order to remove muck from the tunnels more quickly (P. J. Kassouf, personal communication,

February 22, 2015). Next, the “Concrete Down Holes” entry under, “Tunnels Including Adits:

Concord Street Tunnel,” refers to part of the process used to line the tunnel shafts with concrete.

Every lateral 800 ft., the joint venture drilled a hole down to the depth of the tunnel, lined the

hole with steel, positioned a hose over the empty concrete forms surrounding the tunnel, and


pumped concrete through the hose to fill the forms (P. J. Kassouf, personal communication,

February 22, 2015). Thus, the term “Concrete Down Holes” is a name given to the holes drilled

into the ground during this procedure. Finally, any reference to the mobilization or

demobilization of equipment simply indicates the transportation of tools and machinery to and

from a construction site.


Decreased Slope of the Market Street Tunnel

Equipment Needed to Mine Tunnel with 2.34% Grade Cost of

Equipment

Minimum of Two TYS-32 Winch Misc M2030 Hydraulic Winches by Markey Machinery

$95,000.00

Two No: PD605181-INT Electrical Submersible Drainage Pumps by

Grindex

$17,200.00

6000 ft. of 2 in. Extra Improved Plow Steel, Right Regular Lay Cables by Web Rigging Supply

$82,314.00

Minimum of Four Laborers to Operate Hydraulic Winches and to Monitor

the Integrity of Cables

$220,000.00

Additional Four Months of Excavation Time $544,000.00

Total Savings

$958,514.00

The data for the overall cost of decreasing the slope of the Market Street Tunnel is based

on quotes from equipment manufacturing companies and conversations between the researcher

and Paul Kassouf, Stephen O’Connell, and Matthew Kassouf. Because the joint venture did not

mine the tunnel at a 2.34% slope, it is not necessary for the researcher to include “Before Change

Order” and “After Change Order” columns within this table because none of the listed equipment

was used during the excavation of the tunnel.


Connection to Concord Street Pump Station vs. Calhoun Street Tunnel

Construction Procedure Before Change

Order: Cost to

Connect Concord

Street Tunnel to

Calhoun Street

Tunnel

After Change

Order: Cost to

Connect Concord

Street Tunnel to

Concord Pump

Station

Cost Before

Change Order

– Cost After

Change Order

Set up for Transition Tunnel Connecting Concord Street

Tunnel to Calhoun Street Tunnel

$0.00

Inspection of Calhoun Tunnel $10,000.00 $10,000.00

Transition Tunnel Excavation

*Following the change order, the

transition tunnel was designed with different dimensions to connect the Concord Street

Tunnel to the Concord Street Pump Station wet well.

$75,000.00 $40,000.00 $35,000.00

Set Concrete Forms and Pour Concrete for Transition Tunnel

$95,000.00 $40,000.00 $55,000.00

Strip Concrete Forms, Clean and

Patch Final Transition Tunnel Liner

$5000.00 $8000.00 -$3000.00

Set Flumes to Drain Calhoun Tunnel

$25,000.00 $25,000.00

Break Out Calhoun Tunnel $30,000.00 $30,000.00

Clean Transition Tunnel Connecting Concord Street

Tunnel to Calhoun Street Tunnel

$10,000.00 $10,000.00

Probe Cooper Marl from Concord Street Tunnel to

Concord Street Pump Station Wet Well

$40,000.00 -$40,000.00

Inspect Concord Street Pump Station and Remove Debris from Wet Well

$30,000.00 -$30,000.00


Drain Concord Street Pump Station Wet Well

$25,000.00 -$25,000.00

Break Out Concord Street Pump

Station Wet Well Wall

$50,000.00 -$50,000.00

Post Construction Cleanup and

Demobilization of Equipment

$10,000.00 -$10,000.00


$250,000.00 $243,000.00 $7000.00

To clarify, “Inspection of Calhoun Tunnel,” means that the engineers would have walked

through the Calhoun Tunnel to note any large debris that could have inhibited their construction

of the transition tunnel (P. J. Kassouf, personal communication, March 7, 2015). Next, the

“Flumes” that the engineers would have used to drain the Calhoun Tunnel are drainage pipes.

Lastly, the joint venture needed to “Probe [the] Cooper Marl from [the] Concord Street Tunnel to

[the] Concord Street Pump Station Wet Well” to ensure that no air pockets had formed above the

concrete connecting these two structures (P. J. Kassouf, personal communication, March 7,

2015). Had the engineers allowed air pockets to form in the Cooper Marl, the stability of the

ground directly above this section of concrete would have been compromised. In other words,

the Cooper Marl would have settled around the concrete, thus creating potholes and other such

cave ins at ground level.


Final Lining of the Market Street Tunnel

Construction

Procedure

Cost Before

Change Order

Cost After

Change Order

Cost Before Change Order –

Cost After Change Order

Installation of

Rebar

$200,000.00 $200,000.00

Installation of Tie-Wire

$50,000.00 $50,000.00

Steel Forms $48,000.00 $96,000.00 -$48,000.00

Concrete Down

Holes

$160,000.00 $360,000.00 -$200,000.00


$458,000.00 $456,000.00 $2000.00

Due to the change order, the joint venture used a cast-in-place concrete mix containing

polypropylene fibers to line the tunnel. However, the cost of pouring the concrete did not change

as a result of the change order. Furthermore, the engineers used steel forms inside the tunnel to

set the concrete mix.


Elimination of Ground Freezing

Construction Procedure Cost Before Change Order

Traffic Control for Concord Street $5000.00

Mobilization of Equipment $100,000.00

Brine Installation $500,000.00

Brine Maintenance $200,000.00

Post Construction Cleanup and Demobilization of Equipment $28,000.00

Total Savings

$833,000.00

The data for the overall cost of using ground freezing at the junction between the

Concord Street and Calhoun Street tunnels is based on quotes from equipment manufacturing

companies and conversations between the researcher and Paul Kassouf, Stephen O’Connell, and

Matthew Kassouf. Because the joint venture did not use the ground freezing method, it is not

necessary for the researcher to include “Before Change Order” and “After Change Order”

columns within this table because none of the listed equipment was used during the excavation

of the tunnel.


Total Savings

Modification Total Savings

Increased Depth -$2,956,950

Decreased Slope $958,514

Connection to PS $7000

Final Lining $2000

Elimination of Ground Freezing $833,000

-$1,156,436


Chapter V

Through this thesis, the researcher has examined the cost efficiency of the Market Street

Drainage Improvements Project in terms of the money saved by the City of Charleston. To

conduct this case study, the researcher has identified five major modifications made to the

original design plans for this tunneling project. By analyzing the construction process associated

with each blueprint revision, the researcher has compiled qualitative data that explains each

design revision. Additionally, the researcher has assembled quantitative data in the form of price

charts that correspond to each structural alteration. In this way, the researcher has established

sufficient information to draw conclusions regarding the cost efficiency of the Market Street

Drainage Improvements Project.

Principal Findings and Interpretation of Data

From the most expensive revision to the least expensive, the blueprint modifications are

the increase in the tunnel’s depth, the decrease in the tunnel’s slope, the elimination of ground

freezing at the tunnel’s junction with the Calhoun Street Tunnel, the tunnel’s connection to the

Concord Pump Station, and the tunnel’s specialized concrete liner. First, the augmented depth of

the tunnel raised the cost of the project by nearly three million dollars; however, this was the

only alteration that increased overall project expenses. Next, decreasing the tunnel’s slope and

eliminating the use of ground freezing lowered project costs by nearly one hundred thousand

dollars each. In addition, the tunnel’s connection to the Concord Pump Station rather than the

Calhoun Street Tunnel decreased project expenses by seven thousand dollars. Finally, the

changes to the cast-in-place concrete tunnel liner saved the City of Charleston two thousand

dollars.


Based on the qualitative and quantitative data, the researcher can conclude that the

increased depth of the Market Street Tunnel proved the most expensive for the City of

Charleston because it affected the entire structure of the tunnel. By lowering the tunnel, Triad

Midwest Mole provided for a significantly wider buffer zone between the Market Street Tunnel

and the deteriorated Cooper River Tunnel. Additionally, this decision required the joint venture

to increase the depth of the adjoining tunnel shafts. Because more material was needed to

construct the access and drop shafts, the cost of installing the tunnel increased substantially.

Although the construction procedures required to extend the tunnel shafts increased total project

costs by approximately 1.6 million dollars, these design changes did not comprise the majority of

the cost differences between the original blueprints and the modified plans.

Following the increased depth of the tunnel, the most expensive design modifications

were the decreased tunnel slope and the elimination of ground freezing. Unlike the former

alteration, however, these structural changes saved the City of Charleston money because they

involved the subtraction of materials from construction procedures. By changing the slope of the

tunnel from 2.34% to 0.082%, Triad Midwest Mole avoided the use of additional equipment,

laborers, and time to construct the tunnel. Similarly, removing ground freezing from the design

plans made it unnecessary for the joint venture to purchase extra equipment and to hire a

subcontractor to install brine. Thus, the decreased tunnel slope and the elimination of ground

freezing saved the City of Charleston money because they both simplified the construction of the

Market Street Tunnel.

Implications

Because the Market Street Drainage Improvements Project is the second deep tunnel

system to be installed in Charleston, the success of this drainage network will confirm this design


as a solution to flash flooding for the downtown area. Furthermore, the efficiency of this

stormwater tunnel, coupled with that of the Calhoun Tunnel, may prompt the City of Charleston

to initiate similar deep tunneling projects in the future. Moreover, the design changes regarding

the tunnel liner and the use of ground freezing may encourage civil engineers to further test the

stability of the Cooper Marl. Because this geological substance has proven durable in past

tunneling projects, it is likely that tunneling engineers in Charleston will continue to rely on its

strength in the future.

Limitations

The most significant limitations that the researcher encountered during the course of this

study resulted from the written discussions of the decreased tunnel slope and the elimination of

ground freezing. Because the costs for these procedures were determined using lists of

hypothetical materials, the researcher cannot guarantee that the data assembled for these

alterations is completely accurate. However, the information presented as qualitative and

quantitative data for both of these design modifications has been approved by Triad Midwest

Mole engineers. Moreover, an additional limitation arose during the discussion of Division III of

the Market Street Drainage Improvements Project. This phase of construction is currently under

bid; thus, the researcher was not able to fully explain the effect this stage will have on urban

flash flooding in Charleston. Despite this lack of information, this limitation does not affect the

researcher’s ability to answer the governing question.

Summary

The researcher’s purpose in conducting this study was to examine the proposed changes

to the original plans for the Market Street Drainage Improvements Project and to analyze how


these modifications affected the cost efficiency of the project in terms of the money saved by the

City of Charleston. According to the researcher’s calculations, the City of Charleston did not

save money as a result of the blueprint alterations. In fact, the difference between the cost of the

initial design and the cost of the design after the change order is $1,156,436. While the revisions

made to the plans for the Market Street Tunnel decreased the cost efficiency of the construction

process, the researcher is confident that they increased the time efficiency and the safety of the

project as a whole. Moreover, modifications that helped to ensure on-site safety included the

increased tunnel depth, the decreased tunnel slope, and the tunnel’s connection to the Concord

Pump Station rather than the Calhoun Street Tunnel. Hence, three out of the five alterations

analyzed by the researcher significantly contributed to the engineers ’ safety during the tunnel’s

excavation. Although the City of Charleston could have saved money by rejecting the project

change order, the cheaper design by Davis & Floyd, Inc. may have come at the cost of worker

fatalities, irreparable breaches within the Concord Street and Calhoun Street tunnels, and the

overall failure of Division II. Ultimately, the modifications to the original construction plans for

the Market Street Drainage Improvements Project decreased the cost efficiency of this project by

$1,156,436.


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