Post on 27-May-2018
transcript
1
Evaluation of Geotechnical Hazards
byGeoffrey R. Martin
Appendix B:Evaluation of Geotechnical Hazards
Describes Evaluation ProceduresSoil LiquefactionSoil SettlementSurface Fault RuptureFlooding
2
Evaluation of Soil Liquefaction Hazard
Procedures based on three primary source documents
Evaluation of Soil Liquefaction Hazard (cont.)
Field ExplorationLocation of Liquefiable SoilsLocation of Groundwater LevelDepth of LiquefactionField Exploration Methods
Standard Penetration Test (SPT)Cone Penetration Test (CPT)
3
Evaluation of Soil Liquefaction Hazard (cont.)
CPT Data Evaluation
Scale
RockRip-Rap
Quarry
Zone of Liquefaction
Harbor Bottom Sediments
CPT-3 B-1X X'
Elev
atio
n (ft
)Sand
Sand to
0 20 40 feet
(Hydraulic Fill)Silty Sand
-60
-40
-20
0
+20
Key
4(13)
7(31)
40(31)
44(>60)
34(7)7
(13)11(13)18
(>50)17
(>50)
32
>50(>50)
(>50)>50(>50)>50(>50)>50
>50
SMSMSMSMSMSMSMSMSM
SP-SMSP-SM
CLCLMLMHMHSCSCSP
SMSMSMSMSMSM
SM
0 200 40048400
Tip
Res
ista
nce
(tsf)
Fric
tion
Rat
io(%
)
CPT-1CPT-2
0 200 40048
0 200 40048
Tip
Res
ista
nce
(tsf)
Fric
tion
Rat
io(%
) Tip
Res
ista
nce
(tsf)
Fric
tion
Rat
io(%
)
SPT
Blo
wco
unts
(N
)
Soil
Cla
ssifi
catio
n (U
SCS)
Backfill
RunFill
(22)
Clay / Silt(Lagoonal Clay)
Marine
Sand to Silty Sand(Lakewood-San
Pedro Formation)-120
-100
-80
Evaluation of Soil Liquefaction Hazard (cont.)
CPT Data Evaluation 0 40
-80
-60
-40
-20
0
20
Recorded SPT Blowcounts
Interpreted SPT Blowcounts from CPT Sounding
GroundEl. = +13 ft
6020
Field Measured BlowcountN (bpf)60
Elev
atio
n (ft
)
DescriptionInterpreted/Observed Soil
B-1 CPT-3
SM
SM
SP-SM
CL
ML
MH
SP-SCSC
SP
SM
MLSM
SM
SP
CL
ML
CLSP/SCML/SMSP-SM
ML
4
Evaluation of Soil Liquefaction Hazard (cont.)
Evaluation of Liquefaction PotentialSimplified procedure based on empirical observations
Used for most routine projects
More rigorous numerical modelingSites where liquefiable soils extend to significant depthsSites that have significant interlayeringSites where ground remediation costs are high
Evaluation of Soil Liquefaction Hazard (cont.)
Simplified procedure for Evaluating Liquefaction Potential
Factor of Safety =
CRR determined from empirical charts based on SPT or CPT dataCSR determined from design peak ground accelerations
Cyclic Resistance Ratio (CRR)Earthquake Cyclic Stress Ratio (CSR)
depth
CSRCRR
Liquefiable zone
5
Evaluation of Soil Liquefaction Hazard (cont.)
Simplified Procedure: CRR from SPT Data
Evaluation of Soil Liquefaction Hazard (cont.)
Simplified Procedure: CRR from CPT Data
6
Evaluation of Soil Liquefaction Hazard (cont.)
Simplified Procedure: CSR Determination
Evaluation of Soil Liquefaction Hazard (cont.)
Liquefaction Hazard AssessmentFlow FailuresLimited Lateral SpreadsGround Settlement
Choice of Factor of Safety – Depends on:Vulnerability of StructureAcceptable Level of RiskDamage PotentialDesign Earthquake MagnitudeValues to Warrant Hazard Assessment could range from 1.0-1.3
7
Evaluation of Soil Liquefaction Hazard (cont.)
Flow FailuresPotential massive translational failure when static factor of safety <1 where post-liquefaction undrained residual strength mobilized.
Evaluation of Soil Liquefaction Hazard (cont.)
Lateral SpreadingProgressive down slope deformation under cyclic inertial loading during time intervals when F.S.<1Four approaches to assess the magnitude of lateral spread displacement:1. Youd et. al empirical approach2. Newmark time history analyses3. Simplified Newmark Charts4. Numerical Modeling
8
Evaluation of Soil Liquefaction Hazard (cont.)
Youd et. al empirical approach
Evaluation of Soil Liquefaction Hazard (cont.)
Newmark time history analyses
9
Evaluation of Soil Liquefaction Hazard (cont.)
Newmark time history analyses
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30
ky (g)
Gro
und
Dis
plac
emen
t (ft)
HM HM-
LP LP-
IMP IMP-
DUZ DUZ-
ERZ ERZ-
IMPV IMPV-
KOBE KOBE-
upperbound
lowerbound
Evaluation of Soil Liquefaction Hazard (cont.)
Newmark time history analysis – Simplified Charts
10
Evaluation of Soil Settlement HazardTokimatsu and Seed (1987) Methodology
Evaluation of Surface Fault Rupture Hazard
Studies to Refine Definition of Hazard
Location of fault tracesTiming of most recent slip activelyGround rupture characteristics
11
Evaluation of Surface Fault Rupture Hazard (cont.)
Fault Displacement Evaluation
Observation from past earthquakesEmpirical relationship to earthquake magnitudeValues based on fault slip rate