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City of AustinWater Treatment Plant No. 4
June 23, 2017
Raw Water Tunnels
John N. Buser, PE
AGENDAProject History and Overview
Raw Water System Design and Construction
Project Delivery
Key Tunneling Risks
Conclusions
Project History and Overview
Project History and Overview
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 4
Project History and Overview
WTP4 History• 1980 - 2000• 2000 – 2010• 2010 - 2014
Project Location• RM620 and Bullick Hollow Road
o Off-site Pump Station
Project Construction• Alternative Delivery
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 5
Project History and Overview
Project Components• Raw Water Intake (300MGD)• Raw Water Tunnel (300MGD)• Raw Water Pump Station
(50MGD)• Raw Water Transmission Main
(150MGD)• Water Treatment Plant
(50MGD)• Jollyville Transmission Main
(150MGD)
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 6
Project History and Overview
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 7
Project History and Overview
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 8
Raw Water Intake
Raw Water Tunnel
Raw Water Pump Station
Raw Water Trans. Main
Water Treatment Plant
Project History and Overview
Team Qualifications• Knowledge of local geologic
conditions• Specialty Tunnel Expertise• Specialty Structural Expertise
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 9
Project History and Overview
Raw Water Intake• 300 MGD capacity• Sloping Intake on Bottom of Lake
Travis• Three Intake Elevations
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 10
Project History and OverviewRaw Water Intake
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 11
Project History and Overview
Raw Water Tunnel• 300 MGD capacity• 75 ft below Lake Travis• 450 ft below the Surface
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Project History and Overview
Raw Water Pump Station• 50 MGD capacity• Vertical Turbine Pumps• Expandable to 150MGD• 2nd Station for 300MGD
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 13
Project History and Overview
Raw Water Transmission Main• 150 MGD capacity• Portal Entry, Steel Liner• Two 150MGD Tunnels
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Raw Water System Design and Construction
Raw Water System Design and Construction
The Raw Water system has to accommodate fluctuating lake level
• 614ft-msl to 711ft-msl
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And then there was a drought
Raw Water System Design and Construction
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 17
Raw Water Tunnel
Raw Water Trans. Main
Raw Water System Design and Construction
Intake Removes Water From Three Different Lake Levels• 568 Ft-MSL• 607 Ft-MSL• 652 Ft-MSL
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Raw Water System Design and Construction
Large % of tunnel & underground project cost in the excavation
Underground construction subject to unknowns
Materials for Excavation • the (Soil, Rock) properties
can vary considerably
Means and Methods• Tunnel Boring Machine (TBM)• Roadheader• Support
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Raw Water System Design and ConstructionTunnel Easements and Alignment
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Raw Water System Design and ConstructionGeotechnical Investigation
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Raw Water System Design and Construction
Geotechnical Investigation• Number Of Borings
o Supplemental Data
• Geotechnical Data Reporto Used by designers to locate tunnel elevation
• Three Main Geologic Stratao Edwards Limestoneo Walnut Limestoneo Glen Rose Limestone
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 22
Raw Water System Design and Construction
Geotechnical Baseline Report• Contract document that provides interpretations and baseline statements
(means of apportioning risk sharing)• Translates data into conditions for bidding• Not a warranty that conditions will be encountered• Baseline will be used when interpreting the Differing Site Conditions Clause• Example: For baseline purposes, the Contractor shall assume that 15% to
20% of the tunnel alignment will encounter mixed face (rock & soil) conditions.
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Raw Water System Design and Construction
Raw Water Tunnel Challenges• Temporary Support• Permanent Lining• Access Shaft• Connection to Intake• Material Transport• Muck Hauling
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Raw Water System Design and Construction
Raw Water Tunnel Temporary and Permanent Support
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Raw Water System Design and Construction
Raw Water Tunnel Access Shaft
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Raw Water System Design and Construction
Raw Water Tunnel Intake Connection
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Raw Water System Design and Construction
Raw Water Tunnel Intake Connection
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Raw Water System Design and Construction
Raw Water Tunnel Material Transport
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Raw Water System Design and Construction
Raw Water Tunnel Muck Hauling
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Raw Water Access Shaft
Trans. Main Portal
Raw Water System Design and Construction
Raw Water Transmission Main Challenges• ROW• Temporary Support• Permanent Lining• Access• Connection to WTP• Material Transport• Muck Hauling
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Raw Water System Design and Construction
Raw Water Transmission Main ROW
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Raw Water System Design and Construction
Raw Water Transmission Main Support and Lining
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Raw Water System Design and Construction
Raw Water Transmission Main Access
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Raw Water System Design and Construction
Raw Water Transmission Main Connection at WTP• Passed through Multiple
Formations• Thrust Restraint
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Gravel Collar in Edwards
Project Delivery
Nature of tunneling contractors• Generally small, close-knit community• Good understanding of project risks & contract savvy • Frequently team on large projects
Contractor’s expectations• Contract documents tailored to industry standards
o Differing Site Conditions (DSC), Geotechnical Baseline Reports (GBR), Dispute Review Boards (DRB)
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 36
Project Delivery
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels
Construction Manager at Risk• COA selected CMAR delivery method• Obayashi Construction for the Tunnels • Joint Venture – Hill Country Contractors (Manson and Obayashi)
Engineer’s Role During Construction• Daily Inspection / Logs / Photos• Monitor Alignment of Access Shaft / Tunnel• Monitor Vibration
Page 37
Key Tunneling Risks
Insufficient geological informationUnstable face during tunneling Settlement and damage to structuresGassy tunneling conditionsGroundwater InflowsMixed-face tunneling conditionsChoice of primary liningInexperienced personnel
Disruption to residents and loss of public amenity
Disruption to business commerce
Disruption to traffic increased accidents
Disruption to adjacent utilities
Environmental impacts
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 38
Conclusions
Understand the Geology• Mapping, Borings, Geophysics• Analysis using experienced
tunnel personnelProvide accommodations in design for variable tunneling methodsIndependent Peer ReviewAllow adequate Bid TimeDisclose all Subsurface information to biddersEstablish a Dispute Resolution Board
Anticipate access, hauling, and materials delivery challenges
Contractor is responsible for selection of Means of Construction, Equipment, and Methods for execution of work
Contractor retains responsibility for Safety & Excavation
Conduct pre-construction condition surveys
Establish Construction Monitoring Program
Be Flexible
June 23, 2017Water Treatment Plant No. 4 –Raw Water Tunnels Page 39
Thank You
June 23, 2017
