Geotechnical Studies and Trenchless Planning For EBMUD’s ......Geotechnical Studies and Trenchless...
Transcript of Geotechnical Studies and Trenchless Planning For EBMUD’s ......Geotechnical Studies and Trenchless...
Geotechnical Studies and Trenchless Planning For EBMUD’s Orinda Water Treatment Plant Disinfection Improvements Project
Justin Reeves, PE – McMillen Jacobs Associates Jeff Bandy, PE – East Bay Municipal Utility District 1897
Introduction and Background • Disinfection Improvements Project • Orinda Water Treatment Plant • Project Elements
– UV/CCB Complex – Yard piping
Geotechnical Studies • Review and research • Site investigation • Below-grade structures Trenchless Planning • Pipe connections • Methods considered
Presentation Outline
• Constructed in 1935 • Over 800,000
customers • Provides >50% of
treated water for EBMUD
• Capacity: – 175 MGD continuous – 200 MGD instantaneous
• In-line filtration via sand and anthracite filters
Orinda Water Treatment Plant
Existing ORWTP Process and Drivers for this Project
Ammonia Orinda WTP
Filters
Coagulant
Aqueducts
Aqueduct Chlorine
In-line filtration: No sedimentation basin
Disinfection upstream of filtration
No clearwell: Claremont Tunnel acts as storage
Claremont Tunnel
Drought + Aqueduct Chlorination = More DBPs
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Tota
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ppb
Highest Locational Running Annual Average by Quarter
Maximum Level = 80 ppb
• Below-grade UV/CCB complex: 200 MGD low
pressure high output UV system and 1.4 MG chlorine contact basin
• New piping connections: 78- to 108-inch diameter yard piping
• Additional chemical feed and monitoring points • New electrical building and generator house to
support the new system • Modifications to the raw water spillway
OWTP Disinfection Improvements Project
Multiple benefits of selected project: • Maintains gravity flow through plant, adds storage • Multi-barrier disinfection for Giardia (UV) and virus
(CCB) inactivation • Meets regulatory approval: other large (>300 MGD)
UV facilities in California • Cuts DBPs in half by shifting to post-filter
disinfection • Comparable or lower lifecycle costs than other
alternatives • Relatively small footprint
OWTP Disinfection Improvements Project
Site layout and location of UV/CCB facility
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UV/CCB
Filters
Claremont Tunnel to distribution
Isometric View of UV/CCB
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1.4 MG CCB: 3 log virus inactivation
200 MGD UV facility: 1 log Giardia inactivation
Influent Effluent
Section View of UV/CCB
Flow path
• UV/CCB complex – 8,500 ft2 footprint – Basement floor 60-feet below grade
• Piping connections – 5 connections to the new complex – 78- to 108-inch diameter
Focus of the Geotechnical Studies
UV/CCB
• (Qoa) Alluvium and alluvial terrace (steam) deposits;
• Clay, sand, gravel, cobbles, and boulders
• (Tor) bedrock • Interbedded claystone,
siltstone, sandstone, and pebble conglomerate
Geotechnical Studies Project Area Geology
Pebble conglomerate (sample depth of 85ft)
• Region subject to ground shaking
• Nearest active fault is the Hayward Fault
California Earthquake Hazards
• Project subject to ground shaking
• 0.70 g (PGA)
No evidence of active faulting
Earthquake Shaking and Faulting
• Site not covered in landslide deposits
• (A) Large ancient landslide was mapped immediately west of the project area. Developed as a golf course and residences.
Slope Stability and Landslide Deposits
N
• Creeks (A) • Railroad (B)
• Previously occupied by
orchards, sheds, and barns
Historic Topographic Maps 1897 1897
N
• District Construction • Lafayette and
Claremont Tunnels • By the late 1920’s
• District garages,
bunkhouses, and offices prior to construction of the existing plant
• Creek once passed through the project area and has been captured within three 12-inch diameter pipelines to San Pablo Creek
Historic Maps 1925
UV/CCB
Historic Aerial Photos
1963 1939
2018 Plan 2010
Project Area Map Geotechnical borings and geophysical surveys
Project Test Borings
Utility potholing
Sonic boring
Test Dewatering Well Drilling
Groundwater Monitoring Wells
Test Boring Samples and Field Testing
Continuous Core Samples
Exposed rock hardness
Groundwater Level Monitoring
Identify Material Transitions
Develop Schematic Boring Profile
• Rock analysis • Site inspection • Seismic refraction
Summary Rock Strength and Rippability
Rippability
• UV/CCB floor slab 60-feet below-grade • Alluvium with cobbles • bedrock
Excavation support • Secant pile, waler, and strut • Provides groundwater cut-off • Can be installed in cobble rich
material • Incorporated structurally as
part of the final basement wall of the UV/CCB complex
Summary of Excavation Support
• Three feasible methods were considered • Open cut installation • Pipe jacking • Hand mined tunnel
Yard Piping Connections Installation Method
Performance Score
Probable Cost ($M)
Hand Mined Tunnel 73% 16.7
Open Cut 73% 10.5
Pipe Jacking 70% 8.2
Abundant below-grade utilities
• Soil with gravel and cobbles • Below the groundwater table • Bedrock
Schematic Pipe Profile
Change-in-Reach ground conditions
Tunneling Reach
Inside Diameter
(in) Length
(ft)
Invert Depth
(ft) UV/CCB Connection
A 78 45 33 Effluent No. 2
B 108 70 38 Combined Effluent No. 1 & 2
C 48 90 25 Connection to Los Altos
Pumping Plant 108 90 25 Connection to Claremont
Tunnel for distribution D 108 50 25
Hand Mined Tunnel
Grouted Canopy Tubes
Hand Mined Tunnel
1961 Effluent No. 2 and Claremont Tunnel Connection
Hand Mined Tunnel
Modern Construction
Open Cut – 1961 Effluent No. 2
Benched trench excavation
Crossing pipe support
Trench shoring
20ft
• (A) UV/CCB structure excavation as Launching Pit to launch three drives
• Thrust block
• (B) Shared Reception and Jacking Pit to launch one drive
• (C) Reception pits and connection to Effluent No. 2 and the Claremont Tunnel
Proposed Pipe Jacking and Connection Shafts
• Vertical faced shield with small sand shelves at a small vertical spacing.
• The sand lies, at its angle of repose, on each shelf as the shield is advanced.
• Shelves can be removed for full face access.
Pipe Jacking
Pumping Test
• Reduce THM’s concentrations • New disinfection process and facility • Initial design and geotechnical investigation • Yard piping installation challenges
Final Design • Data gathering • July 2020 • Construction planned for 2021
Summary and Final Design
• Carollo Engineers
- Tomas Gillogly, Chris Cleveland, Peter von Butcher, and others
• EBMUD – Matt Guihan, Chris Burquez, and others
• MJA – Tom Pennington, Dru Nielson, Mark Lawrence, and others
• Viking, Cascade, and Pitcher Drilling • NorCal Geophysical • JD Corrosion and Cooper Testing • U.S. and California Geologic Service • Exaro Technologies
Acknowledgments & Questions