Silicon Valley Clean Water Tunnels

Sewer Tunnel Innovation in Silicon Valley

Bruce Burnworth, Project ManagerBreakthroughs in Tunneling Short Course

Chicago August 2017

Regional Environmental Sewer Conveyance Upgrade

WEST BAY SANITARY DISTRICT

SAN CARLOS

BELMONT

MENLO PARK

WOODSIDE

EMERALD HILLS

REDWOOD CITY

Three Major Innovations

Progressive Design Build for a Tunnel

Multiple Layers of Defense against Sewer Corrosion

Diurnal and Wet Season Equalization

Need for Project

Community Reaction to Open Cut HDPE:

The Black Dragon

140 Alternatives Considered2012 - 2014Open Cut in StreetOpen Cut in LeveeLay in SloughLay in LagoonMicrotunnel (shallow)

2014 - 2015Microtunnel (deep)Tunnel Boring Machine (deep)

From SVCW PlantFrom near Airport

Sliplining (w/ bypass)Parallel Smaller PipesPipe Bursting (w/ bypass)Pipe Splitting (w/bypass)Swege (w/bypass)Replace in place (w/bypass)

Evaluation Basis

SUCCESS FACTORS

RISK FACTORS

Evaluate Capital and Life Cycle Costs

Identify probability of risk & consequence of undesired outcome

COSTS

How well does each alternative match up

with SVCW definition of success

5 Alternatives Evaluated & Scored

4BE 4DE

5AE

6AE

7

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Ris

k Sc

ore

Success Score

Conveyance Alternatives: Risk vs. Success Scores

Biggest Challenges

Cost

– 2013 CIP budget: $65million

– Current project budget: $220 million

– Current project cost estimate: $275 million

Schedule

– Current pipeline failing

– Risk of catastrophic failure increasing over time

– Current schedule: completion 2024

100 year life requirement

Approach

Progressive Design Build

Faster Completion

Leaner Project – Better Value

Alternative Corrosion Protection Approaches

Lower Life Cycle Cost

WATS modeling

Increase Project Value

Diurnal Flow Equalization to Reduce WWTP Future Costs

SVCW Progressive Design Build

Two Step Selection Process1. RFQ with SOQ and Interviews to arrive at Shortlist

2. RFP 10% design with Confidential Meetings and Interviews

Two Stage Design-Build AgreementStage 1: Design from 10% to 60% collaborativelyStage 2: Complete Design and Construction

Multiple Phases of Construction (conceptual)

Stage 2A: TBM Ordering, Segment Mold OrderingStage 2B: Shaft Construction, Segment FabricationStage 2C: Tunnel ConstructionStage 2D: Connections

Progressive Design-BuildAdvantages Disadvantages

Faster start and completion Not done previously for tunnels in USA

All parties at the table during design & construction

No firm price when Design-Builder selected

Combination of all good ideas from owner, designers, contractors - creativity

Requires openness and solid project management skills

Early contractor involvement Requires method to confirm that pricing is competitive (sub bids and independent reviews)

Flexibility to achieve project objectives Strong trust needs to be developed

Single-point responsibility for design-build

Ability to control costs and transparency

Minimize confrontational contracting –minimize contract change orders, claims and lawsuits

Progressive Design Build Status

• Three teams shortlisted:

– Barnard/Bessac/Arup

– Kiewit/McNally/Stantec

– Obayashi/JayDee/McMillen Jacobs

• Interviews: August 9 and 10

• Stage 1 Design-Build Agreement: Sept./Oct.

• Start of Construction: 2018

• Completion: 2020 to 2024 (TBD)

Corrosion Protection

• Current estimate includes $90 million to put a pipe inside the tunnel

• Alternatives:

– HDPE lining (several methods)

– Multiple layers of defense including upstream dosing

Multiple Layers of Defense

• Upstream dosing to eliminate sulfides

• Sacrificial concrete thickness

• Enhanced air movement

• Corrosion resistant concrete

• Laminar flow design

• Biocide concrete additive

• Monitoring and inspections

WATS ModelWastewater Aerobic/anaerobic

Transformations in Sewers

Developed over 3 decades at Aalborg University, Denmark.

Computer simulation of all relevant biological, chemical and physical processes including inter-phase mass transport, wastewater hydraulics and sewer air . . . using a matrix of non-linear differential equations

Microbially Induced Corrosion

• Formation of H2S in biofilm • Chemical oxidation of sulfide in bulk

water • Biological oxidation of sulfide in bulk

water • Biological oxidation of sulfide in

biofilm • Emission of H2S from water phase to

gas phase • H2S oxidized to sulfuric acid on

concrete surface

San Francisco Results & Targets

• Some locations showed that corrosion can results in 5-10 cm (2 – 4 in) over a 100 year period, but in general corrosion is a minor issue in the drainage area

• Recommended Target Parameters– Dissolved Sulfide (DS) < 0.5 mg S/L

– H2S (gas) <10 ppm inside the selected monitoring manhole

– Shear stress >0.5 Pa if a new pipe is installed

Flow Equalization

• Diurnal flows

– Average ~14 mgd

– Each day varies from 2 mgd to 24 mgd

• Wet Season Peak Flows ~103 mgd

– Treatment plant capacity is 80 mgd

– WWTP operates well at 60 mgd

Wet Season Peaks

• With 11’ ID tunnel (pipe in tunnel) additional surface storage needed

• With 13’ ID tunnel (no pipe in tunnel) all equalization can occur in tunnel

Diurnal Equalization

• With 11’ ID tunnel (pipe in tunnel) air flow to plant blocked every day creating upstream odor issues

• With 13’ ID tunnel (no pipe in tunnel)

– all air flows to plant for odor control (dry season)

Hydraulics

San Carlos Drop Structure

Design Storm Equalization

Diurnal Equalization

Tunnel Excavation Rate

• Tunnel excavation rate of 100 feet per day average is expected based on a nearby tunnel project (after first 1,000 feet)

• Soil exploration every 250 feet along the alignment indicates consistent lens for tunneling of upper alluvial sediments (medium stiff clays and sand lenses)

• Herrenknecht thinks that average tunneling rates can be improved significantly with current TBMs by operating the TBMs as a moving production line

Greatest Pleasure

• “Cost of public projects increases” – potentially cutting project cost in half ($275m to $135m)

• “Public projects always get delayed” –potentially cutting project duration in half (2024 to 2020 completion)

• Cost – Schedule – Quality: “You can’t have all three.” I sure try.

• Motivation: Deliver the best possible project.

Questions

For more information and copies of documents visit www.SVCW.org

http://www.svcw.org/projects/SitePages/gravitypipeline.aspx

Regional Environmental Sewer Conveyance Upgrade

Recommended Alternative “4BE”

Solution Varies

• MIC attacks increase in ferocity as temperatures rise, detention times increase, dissolved oxygen is not available, air flow slows, concrete is easily penetrated by acids allowing steel rebar to corrode and concrete spall.

• Corrosion varies dramatically with these variables. Understanding how these variables affect MIC for a specific section of sewer is critical to an appropriate design that defends against MIC attack at every MIC step.

• Future treatment processes only need to be designed for 60 mgd instead of 80 mgd

• If flushing is needed, can be done using upstream pump stations

Notes

• Innovations flow from necessity. A cut and cover HDPE 66” force main sewer project through an exclusive residential neighborhood in Silicon Valley (California) was being referred to as the Black Dragon and was doomed to years of lawsuits. A nearby 5 mile long water tunnel gave us a potential cost effective solution but the need for corrosion protection drove the cost way over budget. Progressive design-build is being used to complete the 3.3 mile long 15’ OD tunnel project to under our budget and ahead of schedule. A multi-layer defense is being studied to more cost effectively address sewer corrosion while diurnal and seasonal flow equalization in the tunnel provide additional value. Additional valuable ideas are expected to flow from the collaborative Progressive Design Build approach.

• SVCW is a public agency joint powers authority that conveys sewage from four cities in Silicon Valley, treats the sewage and discharges it to the San Francisco Bay as clean water.•• Our existing interceptor pipe is more than 45 years old and is failing due to soft soils and corrosion. When the pipe was constructed there were no houses in the area. Now the pipeline

alignment has $2 million houses along tree lined streets. Open trench replacement of the pipe is not acceptable. A 3.3 mile tunnel will be built and serve as a gravity sewer pipeline to avoid major community disruption.

•• Innovative concepts include:• Tunnel to be used for wet season flow equalization to allow 103 million gallons per day (mgd) of storm inflow and infiltration to be equalized to 60 mgd for treatment to lower

treatment costs.• Tunnel to be used for diurnal flow equalization to provide a consistent 12 mgd of flow to the plant 24 hrs per day to equalize the current variation of 2 mgd to 24 mgd flow. This diurnal

flow equalization will further decrease the cost of sewage treatment especially in the area of operations and maintenance allowing more consistent flow and more process automation.• Launch shaft alternative to reduce community and environmental impacts

– A launch shaft on the middle with tunneling in both directions minimizes impacts– A ramped launch shaft at the end on a wildlife refuge and airport clear zone would reduce costs if environmental and safety issues can be addressed.

• Tunnel excavation rate of 100 feet per day average is expected based on a nearby tunnel project (after first 1,000 feet)– Soil exploration every 250 feet along the alignment indicates consistent lens for tunneling of upper alluvial sediments (medium stiff clays and sand lenses)– Elon Musk is challenging the tunnel industry to increase tunneling rates by 5 to 10 times. He plans to use his Tesla production line experience and hiss SpaceX technology to accomplish these higher

production rates.– Herrenknecht thinks that average tunneling rates can be improved significantly with current TBMs by operating the TBMs a moving production line.

• First Progressive Design Build tunnel project in the USA (currently we are in the PDB selection process)– Select Progressive Design Builder (PDB) based on experience, qualifications, approach and price– Stage 1 bring current 5% to 10% design to 60% to 70% design– PDB then provides a fixed price to complete design and construct the project– Owner reviews price and negotiations completed (owner has off-ramps if negotiations not successful)– Stage 2 involves 100% design, construction and start up by PDB– Advantages:

• Practical and innovative ideas brought to project by PDB• Faster completion of project by overlapping design and construction• Minimize confrontational contracting – minimize contract change orders, claims and lawsuits

• Alignment– Horizontal alignment minimizes community disruption

• 3.3 miles through urban area and only four private properties and three public agencies affected.• Private property impacts limited to small corners of parcels to allow reasonable TBM turning radii of 800 foot minimum

– Vertical alignment keeps TBM below soft young bay mud layer in medium stiff clays and sand

• Corrosion protection alternatives– Pipe in Tunnel– Tunnel Lining– Multiple Layer Defense against Corrosion (could reduce project costs by $60 million)

• Corrosion in sewers . . . the process (all of these above steps need to happen to have a concrete structure fail):– Solids in sewage provide a food source for bacteria that create H2S if there are no oxygen or nitrate molecules available. – H2S in solution comes out of solution into the air in the sewer if the pH is low and with turbulence. – H2S in the air is converted by bacteria on the moist surface of the pipe to create H2SO4– H2SO4 eats away at cement paste in concrete

•• Multiple Layers of Defense against Corrosion (a defense for every step of the corrosion process):

– Continuation of upstream Bioxide dosing to reduce H2S formation in the wastewater, – Adjustments to pH and laminar flow to reduce the movement of H2S from water to air,– Enhanced air movement and biocide to reduce conversion of H2S to H2SO4, and– Acid resistant precast concrete tunnel segments with sacrificial thickness to provide for long useful life of the concrete structure in an acid environment. (Metakaolin seems like a great solution for acid resistance . . . early strength and workability

for pre-casters and acid resistance for sewer applications).

•• The above layers of defense act together independently to achieve long concrete structure life with 95% to 99% confidence (joint probability).•• Project: 3.3 miles of 15 foot outside diameter soft ground tunnel with a construction cost of $100 million to $160 million with tunneling scheduled to start in 2018.