9/14/2011

1

Site Location

9/14/2011

2

Cheesman Dam

Cheesman Dam

•Cheesman Dam is a gravity arch masonry dam, faced with granite blocks. First of this type of dam in the United States.

•Dam Height of 221 feet, crest length of 1100 feet (including spillway).

•The dam impounds 79,064 acre feet

History of Cheesman Dam

•Completed in 1905 (1st Dam washed out in Flood of 1900)

•Worlds highest dam at time of construction.

•Outlet Works tunneled through the abutment in 1895

•Auxiliary Outlet Works installed in 1925

•42” Gate Valves Installed behind existing 42” Gate Valves at 80’ (upper) , 60’ (Mid) and 15’ (Low) level’s

•Downstream Valve House installed in 1971

•ASCE National Historic Engineering Landmark designation in 1973

9/14/2011

3

Haymen Fire 2002

9/14/2011

4

Project Need and Purpose

� An Aging Outlet Works dependent and operating on 19th

century technology

� Maintenance of key infrastructure

� A means to contain new sediment loading from Hayman Fire

� Provide upstream control for dam safety

Project Scope� Phase 1 (Completed November 2010)

� Installed 3 new stainless steel slide gates� Installed 3 new trashrack structures� Constructed new control building on the left

abutment� Provided new backup generator

and upgraded the electrical and control equipment throughout the facility

� Phase 2 (Scheduled April 2011 to April 2012)� Remove Larner Johnson Needle Valve� Install new Jet Flow Gate � Decommission all Gate Valves

Cheesman Dam Upstream Control Project

…A Multi-Year – Multi-Phased Project

Purchase Order Purchase Order for Upstreamfor UpstreamSlide Gates Slide Gates

Purchase Purchase Order for Jet Flow Order for Jet Flow

Gate Gate

Phase 1 Phase 1 –– Design, Design, PrePre--QualificationQualification

and Biddingand Bidding

Phase 1 Phase 1 ––Underwater Underwater

Construction (Upstream Construction (Upstream Slide Slide

Gate Installation) Gate Installation) and Phase 2 Designand Phase 2 Design

Phase 2 Phase 2 ––LaborLabor--Intense Intense Demolition/Demolition/

Abandonment and Abandonment and replace Needle Valve replace Needle Valve (1925) with Jet Flow (1925) with Jet Flow

GateGate

20072007

20082008

20092009

20102010

20112011

9/14/2011

5

PHASE I – OVERALL PROJECT PLAN

Outlet Works Orientation

Auxiliary Outlet Works

Primary Outlet WorksLow Level

Mid Level

Low and Mid Level Outlets

Low (15’) Level Outlet

Mid (60’) Level Outlet

Mid (60’) Level Inline 42” Gate Valves

Low (15’) Level Twin Inline 42” Gate Valves

Phase 2Phase 1

9/14/2011

6

Gate Valves at 15’-Level

Inside Water Tunnel at 15’-Level

9/14/2011

7

Auxiliary Level Outlet

Phase 2Phase 1

Orig. Needle Valve Installation

9/14/2011

8

New Jet Flow Gate Testing

Drain or Dive?

Cost Benefit Analysis Conclusion: Avoid water storage shortfall (potential watering restriction) risk by paying premium for Construction Diving

� Cost/Benefit Analysis showed a potential savings of ~20-30% if drained and completed in the “dry”.

� Hydrology Study showed a 30% risk of not refilling the reservoir in the following run-off season.

� Not re-filling the reservoir would lead to system wide impacts and possible watering restrictions.

Phase 1 - Contractor Selection� Deep Underwater Construction

requiring Saturation Diving

� Four underwater contractors were pre-qualified

� Two of the prequalified contractors submitted proposals

� Global Diving and Salvage Selected - $12.7M

9/14/2011

9

Saturation Diving Overview

Step 1: Demolish and remove the existing trashracks

Step 3: Drilling, blasting, and tunnel shaping of the tunnel portals and inlet areas.

Steps 4-7: Install guide tracks, floor grout, spool piece, grout and anchor

Step 2: Detailed survey of the area to compare existing underwater conditions to the contract documents

Step 7: Install New Slide Gate

Step 8: Install New Trashrack

Step 9 & 10: Install and Hookup New Hydraulic Lines - Startup Testing and Gate Commissioning

Construction Sequencing

Auxiliary Overview Video

9/14/2011

10

Project Organization and Decision Tree

Denver Water (Owner /Manager & Design Engineer*)

Global Diving & Salvage

(Contractor)

KOA (Resident Engineer)

*URS provided Design Engineering for Trashracks and Structural Review of Field Engineering Designs

Risk Management

Risk Management Strategy

� Lessons Learned Approach

� Brainstorming Meeting between Owner-Resident Engineer-Contractor prior to each major activity and work area

� Post Issue identification meetings to discuss options: focusing on design criteria and cost

Auxiliary Tunnel

Shapening, $383,000

Auxiliary Trashrack

Modifications, $50,000

Mid Level Tunnel

Shapening, $146,000

Mid Level Rock Fall

Replacement, $136,000

Low Level Masonry Removal, $1,425,000

Major Issues During Construction

9/14/2011

11

Auxiliary Level Tunnel Widening

Issue: Existing tunnel alignment had a bulge on the north side. The bulge prohibited the spool from physically fitting within the tunnel.

Solution: Several alignmentalternatives were evaluated for a best fit and cost analysis. The most cost effective solution was to re-adjust the spool alignment to the south and remove rock from the north wall to allow clearance for the spool.

Total Cost:

$383,000 Alternative EvaluationSavings

$76,000

Auxiliary Level Trashrack Modifications

Issue: Two Major Issues: 1) The Owner-Furnished trashrack fit too snuggly within the design blast. This issue was identified at the project start. 2) The actual tunnel portal geometry interfered with the trashrack base.

Solution: 1)Modifications to the trashracks were completed at the fabricators facility prior to shipment. 2) The fabricator sent a welding team to the site to perform “emergency” modifications while the diving contractor continued contract work

Total Cost: $50,000 Field Engineering Savings: +$40,000

Mid-Level Tunnel GeometryIssue: Site survey showed interference

between trashrack and rock outcroppings,and the spool and tunnel wall.

Solution: Structural criteria limited the ability to modify the trashrack. The trashrack and spool location were slightly modified to limit the required rock chipping areas.

Total Cost:

$146,000 Alternative EvaluationSavings:

$120,000

9/14/2011

12

Mid Level Rock Fall

Issue: Post blast survey showed large area of rock fall, creating a void area above the spool. The condition did not meet the design criteria for rock cover over the spool piece.

Solution: Create a Mass Concrete wedge to fill the void area. The wedge was designed to replace rock and seepage. Value Engineering iterations increased rebar sizing to reduce rock doweling requirements ($$$), resulting in considerable cost savings.

Total Cost: $136,000 Alternative EvaluationSavings:

$60,000

Historical As-Constructed Drawing

Low Level Masonry Removal

Sector Scan Survey of Low Level

9/14/2011

13

Original design based upon photographs and As-Constructed Drawings.

Field conditions evaluated to contain poor quality masonry at end of spool.

Area of CollapseConcern

Reservoir

Hydrostatic

Pressure

P o o rP o o rQ u a l i t yQ u a l i t y

M a s o n r yM a s o n r y

NewExcavation

Solution is to remove the poor quality masonry and reposition the spool and gate further in the tunnel.

Issue: Discovery of masonry material above and behind the spool. The masonry would have failed in unbalanced condition.

Solution Remove all masonry and some rock back an additional 9-feet, reposition spool further within rock tunnel.

Total Cost:

$1,425,000 Risk Directive Savings:

$80,000

~2 X Tunnel Diameter

9/14/2011

14

Critical Success Factors – Phase 1� Provides robust and redundant

control� New Outlet Works System meets

current Engineering Standards� Extremely low leakage rates � No Lost Production Time or

Standby Fees� Due to Partnering between

Owner-Contractor-Resident Engineer

� Risk Register and Pre-Defined Response Plans facilitated efficient solutions

� Minimal disruption to Denver Water’s operations – Full Reservoir throughout Construction

Performance Testing

� Quality Based Selection Process

� Five contractors prequalified

� Four contractors submitted proposals

� Proposals - $2.9 M to $3.9 M

� Moltz Constructors is Low Proposer at $2.9 M, and scored highest in the technical proposal evaluation

� Currently Working on the Primary Outlet Works Decommissioning

� Scheduled to begin Auxiliary Demo and Jet Flow Gate Installation in November

Phase 2 - Contractor Selection and Progress

9/14/2011

15

Low and Mid Level Outlets

Phase 1 Slide Gates and Trashracks

Abandon old gate valves

Auxiliary Outlet Works - Demolition

Phase 1 Slide Gate and Trashrack

Auxiliary Outlet Works New Jet Flow Gate

Hoover Dam Jet Flow Gate Testing (Also replaced old Needle Valves)

9/14/2011

16

Phase 2 - Progress

9/14/2011

17

9/14/2011

18

Questions?

9/14/2011

19

9/14/2011

20

9/14/2011

21