perris dam_godwin et al aeg conf fnl(3)
TRANSCRIPT
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AEG Annual Meeting – Kona, Hawaii, Sept. 22, 2016Technical Session #6
William Godwin, CEG – Lettis Consultants Intl Mike Turner, CEG - AECOMJustin Pearce, CEG – Infraterra (now USACE)Holly Nichols, CEG - CA Dept Water Resources
Perris Dam Seismic Remediation –Geologic Observations from CDSM Foundation Treatment
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Perris Dam-Presentation Topics Introduction History of Perris Dam Physical and Geologic Setting Seismic Remediation Design Elements Cement Deep Soil Mixing Venting Observations Questions
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INTRODUCTIONOwner
California Dept of Water Resources
QC Laboratory
InspectorsAECOM
LCIInfraTerra
DWR
Specialty SubJensen
Drilling Co.Specialty
SubJAFEC USA
General ContractorPulice, Inc.
Bd of Consultants
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INTRODUCTION
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HISTORY OF DAM
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HISTORY OF DAM • Terminal end of
California Aqueduct• Zoned Earth
Embankment, L= 2.2mi., H = 128ft
• Partial core and foundation over-ex (<6ft)
• Construction Completed in 1973
• Capacity – 131,450af• Currently lowered 25ft
to allow 37ft freeboard
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Perris Dam Geologic Setting
USGS OFR 99-172, 2004
San Jacinto FZ
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Geologic Profile – Left Reach
ReservoirA
YA
CPT transect, upstream
SPT transect, upstream
Profile location
Approx Bdrk
?
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Sample Cross-Section, Left Reach
(Friesen and Balakrishan, 2012)
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Seismic Remediation Design Elements
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Seismic Remediation Design ElementsFoundation Treatment and Stability Berm
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Cement Deep Soil Mixing - CDSM Objective: Strengthen the foundation and
along with the stability berm to limit the deformation of the dam to the acceptable level during a strong seismic event
DWR decided against removal and replacement because of shallow groundwater in granular soils… judged they couldn’t dewater sufficiently.
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Seismic Remediation Design ElementsFoundation Treatment
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Typical Cell Layout Down
stream
Longitudinal Wall Segments, Typ.
Transverse Walls, Typ.
Deep Cell PlanShallow Cell Plan
A A Section A-A
Transverse Walls
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CDSM Mixing Rig
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CDSM Predrilling Homogenize alluvial soils by loosening dense
zones, cemented layers and prepare for optimal mixing
Use same equipment as that used in mixing Inject water and air to facilitate advance Advance rate <8ft/min Withdrawal rate <20ft/min Primary/Secondary Installation Sequence
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CDSM – Grout Mixing Introduce cementitious grout to soils at a mix
dosage of 210 kg/m3 and W:C ration of 0.9 Advance rate <4ft/min Withdrawal rate <9ft/min Primary/Secondary Installation Sequence Remix bottom 10ft and other zones
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Required Work Flow – Pre-drill/Mixing
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CDSM – Verification CoringThe recovered samples are checked for recovery and uniformity. • Recovery Criteria: – The recovery from each 5 foot core run should be at least 85 percent. – Continuous core recovery should be at least 90 percent when averaged over all core runs within a single boring. • Uniformity Criteria: – Within a single core run, the sum length of unmixed or poorly mixed soil regions or lumps that extend entirely across the cross section of the core sample (minimum of 2.5 inches) is not to exceed 15% of the core length. – All lengths of unrecovered core shall be assumed to be unimproved soil.
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Verification Coring
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Inspectors Role Serve as DWR representatives Observe CDSM activities, noting geologic
anomalies or variations. Document whether or not construction is
proceeding according to specifications Log element coreholes Choose core samples for cutting Prepare Daily Inspection Reports
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Design Validation Using Geologic Data Review Databases from Contractor and Inspectors and analyze using GIS Preliminary Analysis
Venting – Preferential channel, influence of dewatering Analysis in Progress
Element Advance RatesSpeed with DepthDrilling Resistance – Correlation to Young Alluvium or lower SPT blow CountsRefusals & Restrokes – Correlation with Higher Bedrock and Alluvial Stiffness
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Venting Where did it occur?
– In relief wells upstream and downstream of CDSM pad
– On pad surface– Adjacent to and up to 75ft from predrilling
Preferential alignment upstream and downstream. Distances of venting from predrill were generally less in the cross-valley direction. Possibly occurring along channels
Mostly Venting Less VentingNo Data
Blue = No Venting Noted
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Venting When did it occur?
– During and after Predrilling; not mixing– Could linger after predrilling paddles removed
Why did it occur?– Excessive air and/or water pressure– Bottom line is that we don’t really understand
exactly how the pressures were being transmitted from the column being predrilled
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Ground Venting – Monitoring Wells (video)
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Ground Venting – Ground Surface (video)
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Venting WHAT was the concern?
– Possible hydrofracturing of foundation soils– Possible grout migration. Would be a
particular problem if it contaminated the blanket drain for dam.
– Possible hydrofracturing of CDSM columns as they were curing
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Venting Mitigation – RFI 117 Working air pressures during predrilling will be
monitored and regulated to remain <120 psi. Given the concern that air may damage the dam,
no isolated elements will be predrilled within the length of two (2) elements of the upstream side of the CDSM working platform.
For this purpose, isolated elements are those elements which are more than 12 feet from the nearest predrilled element. This is based on the observation that neighboring predrilled elements will serve as vents.
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Venting – Conditional Acceptance RFI117 Provided DWR and DSOD are able to monitor air
pressures during predrilling Contractor has the ability to effectively control
and adjust air pressures as required during pre-drilling
Significant venting conditions (such as soil erosion) caused by water and pressurized air are avoided during pre-drilling
Engineers has right to halt work if significant venting is observed
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Venting Analysis: Compare with Channel Structure
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Venting Analysis: Overall pattern may correlate with large
channel structure Prominent ‘No Venting’ patches (Cells 34 and
45) within ‘Mostly Venting’ central part of CDSM layout
Blue = No Venting NotedGreen = Venting Noted
Cell 34 Cell 45
Green venting noted Blue venting not noted
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Venting Analysis: Dewatering Observations Observed at Construction Observation Wells COW-15 through COW-25 are located along CDSM
footprint
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Dewatering Observations
1450145514601465147014751480148514901495
Magnitude of Lowering During This Time PeriodFor gray well (COW 22)
=21 ft
Maximum Dewatering Moderate Dewatering
21 ft
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Venting: During Dewatering Period Larger channel structure may contribute to
venting locations Dewatering time periods may correlate with
lack of venting We are still refining the venting/no venting
dataset
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Conclusions CDSM operation completed on May 24, 2016 All cores passed the acceptance criteria and the
percentage of recovery and uniformity rates Venting was most common in the center of the
paleo valley where– Groundwater was shallowest– Highest concentration of coarse grained
deposits exist Venting was much less common in cells
constructed towards the end of the project where groundwater was deeper (south end of the dam)
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Acknowledgements Michael Driller, GE and Grace Chen, PE –
DWR Geotechnical Engineers Joan Weber, PE – DWR Resident Engineer Hans Abrahamson-Ward, CEG – LCI Principal
Geologist Stephanie Briggs, PhD, PG – LCI Sr. Project
Geologist
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Questions