Design and Construction of a 200-foot-deep, 24-foot … PNCWA- Session 21-1... · Design and...
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Transcript of Design and Construction of a 200-foot-deep, 24-foot … PNCWA- Session 21-1... · Design and...
Design and Construction of a 200-foot-deep, 24-foot-diameter Conveyance System
Boise, IdahoSeptember 14, 2009
Placeholder for photo
Conveyance System Access Shaft
Daniel R. Williams, P.E.
Project Overview
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Project Location Map BrightwaterWWTP
BellevueSeattle
EffluentConveyanceSystem
Treatment PlantTreatment Plant
•• 36 MGD in 2010; Peak Flow 130 36 MGD in 2010; Peak Flow 130 MGDMGD•• 54 MGD in 2040; Peak Flow 170 54 MGD in 2040; Peak Flow 170 MGDMGD•• Membrane bioMembrane bio--reactor WWTPreactor WWTP•• Reclaimed water facilitiesReclaimed water facilities
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•• Reclaimed water facilitiesReclaimed water facilities
Conveyance TunnelsConveyance TunnelsLength (feet)
Outside Diameter
East 13,890 18’
Central 19,020 11,590
17’17’
West 21,033 13’
PREDESIGN REPORT:
q Describes a BWP large enough to serve as a retrieval shaft for two TBMs
q Location based maximum tunnel length and
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q Location based maximum tunnel length and depth based on hydraulics
§ Tunnel BT3 is 3.8 miles in length§ Tunnel BT4 is 3.9 miles in length
q Anticipates an inside diameter of 30 feet
Brightwater Effluent System
PROFILE
PLAN
Ballinger Way Portal – Design Phase
TECHNICAL MEMORANDUMS:
q Tunnel and Portal Access TM
§ Describes inspection intervals and access requirements for Brightwater System
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q Technical Advisory Committee Report
requirements for Brightwater System
§ Inspection and maintenance at BWP by remote operated vehicles (10’ x 10’)
§ Proposes a drilled shaft 10 feet in diameter
TASK: Evaluate consequences of reducing the
Ballinger Way Portal – Design Phase
inside diameter of the BWP from 30 feet to 10 feet.
Why reduce the diameter?
• Large diameter BWP could take 15 months to construct at a cost of $13M.
• Drilled shaft BWP could be constructed in several months
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• Drilled shaft BWP could be constructed in several months for a cost of $1.5M.
Problems?
• Complex tunnel-to-portal and tunnel-to-tunnel connections (Drilled shaft not large to receive TBMs).
Soil Conditions at BWP / Tunnel Interface:
Flowing or unstable soil from scattered sand, silty sand, and silty gravel layers; hydrostatic head of 150 feet at base of BWP
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feet at base of BWP
Inspection / Maintenance Requirements:
• Initial inspection after ten years of operation• After 7.0 or larger quake• 30-year intervals• Submersible and crawler-type ROVs
Ballinger Way Portal – Design Phase
ALTERNATIVES:
#1 Small Diameter Portal (i.e., Drilled Shaft)
1a – Portal above Tunnel Intersection
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#2 Large Diameter Portal
1b – Portal West of Tunnel Intersection
1c – Portal East of Tunnel Intersection
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Ballinger Way Portal – Design Phase
Constructability and Risk (Drilled Shaft Alternative):
• Unstable flowing soil conditions where tunnel-to-tunnel and tunnel-to-portal connections occur.• Groundwater pressure at connections is 60-plus psi.
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• Groundwater pressure at connections is 60-plus psi.• Requires grouting (in absence of dewatering) to safely conduct hand-mined excavations.• Effectiveness of grouting is difficult to verify; incomplete grouting could compromise hand-mined excavations, exposing workers and the tunnels to soil and groundwater.• Increases the likelihood of Contractor claims and schedule delays.
Ballinger Way Portal – Design Phase
Schedule Impacts (Drilled Shaft Alternative):
• Drilled shaft cannot be constructed independently of tunnels (so drilled shaft is on the critical path).
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tunnels (so drilled shaft is on the critical path).
Cost (Drilled Shaft Alternative):
• Estimated cost of drilled shaft alternative is $7.2M. Large diameter portal alternative costs ranged from $6M to $14M.
Ballinger Way Portal – Design Phase
ALTERNATIVE #2Large Diameter Portal
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Ballinger Way Portal – Design Phase
TASK: Evaluate the following four alternative excavation support systems:
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– Sequential Excavation w/ Depressurization– Open Caisson– Ground Freeze Wall– Slurry Diaphragm Wall
Ballinger Way Portal – Design Phase
Alt 2a – Sequential Excavation with Depressurization
• Alternative was ruled out because of concerns about volume of groundwater
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concerns about volume of groundwater removal and ability of Contractor to keep shaft dewatered.
Ballinger Way Portal – Design Phase
Alt 2bOpen Caisson
• Alternative was ruled outbecause of concerns about plumbness and keeping
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plumbness and keeping caisson moving downward at the depths required.
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Alt 2cGround Freeze Wall
• Alternative was allowed because of past success on other projects similar in size
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other projects similar in size and scope – represented best chance for success.
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Alt 2dSlurry Diaphragm Wall
• Alternative was allowed because of past success on other projects similar in size and scope – represented best chance
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scope – represented best chance for success.
Ballinger Way Portal – Design Phase
Alternative Costs:
1. Sequential Excavation w/Depressurization -- $8.19M2. Ground Freeze Wall -- $14.56M3. Slurry Diaphragm Wall -- $9.17M4. Caisson -- $6.3M
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4. Caisson -- $6.3M
Ballinger Way Portal – Design Phase
Reclaimed Water Pipeline – Pipe Support Design
• 20-inch diameter pipe, 170-foot-tall column
• Thermal expansion when temp rises from 40-deg to 90-deg = 0.65 inches
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• Thermal expansion when temp rises from 40-deg to 90-deg = 0.65 inches
• Force imparted by “pinned” pipe = 165,000 lbs
Therefore, pipe supports designed to allow for thermal expansion
• Polymer material is placed between the steel “strap” and the pipe itself, which allows the pipe to move vertically within the pipe support.
• Polymer material is used for skids on casing spacers and is used on boat docks.
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