evaluation of liquefaction potential of sub soil
TRANSCRIPT
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8/12/2019 Evaluation of liquefaction potential of sub soil
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Evaluation of LiquefactionEvaluation of LiquefactionEvaluation of LiquefactionEvaluation of Liquefaction
Potential of Delhi SubPotential of Delhi SubPotential of Delhi SubPotential of Delhi Sub----soilsoilsoilsoil
Acknowledgementto
EREC, IMD, DSTCRRI, GSI, DST, CGWB, SOI..
C. GhoshNIDM
P. Mishra & A.K. ShuklaEREC,IMD
Kishor KumarCRRI
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Microzonation Issues of Delhi
Proximity to Himalaya with multiple fault lines
Ridge area and sandy silty soil >300m
Yamuna river basin of Holocene times
Basin Margin and Basin effect Chattarpur area
Mixed built environment
SignificantPastEarthquakeNear Delhi
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Study of liquefaction
Evaluation of liquefaction hazards
Evaluation of potential grounddisplacements
Mitigating liquefaction hazards by suitableground improvement techniques
Parameters required forliquefaction assessment Seismological EQ. Magnitude, source
distance, intensity, PGA,amplification/deamplification factor, spectralacceleration
Geotechnical penetration resistance(SPT/CPT/..), soil type, grain size, thickness of
liquefiable zone, density, water table depth, bedrock depth, .
Built environment Foundation type, zonationcode, Building type, building dimension, soil-structure interaction factor.
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Liquefaction studies of NCTDelhi
Geotechnical data (DDA, CPWD, DMRC..)
(Collected by CRRI (441 reports) andEREC (50 reports)
Total No. of Boreholes = 1950 (CRRI) +
500 (EREC)
One Borehole (from each project) having min N
value and possibleliquefiable soil types (basedon grain size, Liquid limits, density) selected
Modalities of Liquefactionstudies
Depth ranges taken are 0-3m, 3-6m, 6-10m,10-15m and >15m
Water table (as per CGWB, Nov-2004)
PGA values of Delhi region (Sharma et al,2003) [0.19 to 0.33g, M=7.24]
Soil amplification (Rao, 2005)[1.2 to 2.5] Calculation of CRR(Cyclic Resistance Ratio)
& CSR (Cyclic Stress Ratio) for SPT based
on Idriss and Boulanger (2004)
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# Gwt_2004.shp0-210-202-520-405-10> 40
Fs-0-3m.dbf# 1# 2
0 20 40 Kilometers
N
EW
S
Soil Type (0-3m)
Liquefaction (Soil type)
Non-liquefiable type = CL, CI, CH,
Liquefiable type = SP, SM, ML, CL-ML
Liquefaction Susceptability (%)
0
20
40
60
80
100
0-3 (465) 3-6 (489) 6-10 (471) 10-15 (353) >15 (228)
NON-LIQUEFIABLE SOIL LIQUEFIABLE SOIL
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Ground water depth rangeGround WT Depth as per CGWB (491
Locations)
4.3
28.1 27.3
18.1
22.2
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
0-3 3-6 6-10 10-15 >15
Depth Range (m)
BoreHoles(%)
Bore hole depthBore Hole Depth (491 Locations)
1.0
15.1
27.9
23.2
9.4 9.4
14.1
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
30
Depth Range (m)
BoreHoles(%)
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SPT valuesN-Values at different depth ranges
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
0-3
(465)
3-6
(489)
6-10
(471)
10-15
(353)
>15
(228)
Depth Range (m)
N-Values(%
30
SPT values
N-Values at different depth ranges
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
30
Corrected N-Values
N-Values(%)
0-3 m (465 No.) 3-6 m (489 No) 6-10 m (471 No.) 10-15 m (353 No.) >15 m (228 No.)
SPT values Lique potential
30 V. low
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Liquefaction opportunity
Liquefaction Opportunity (%)
0
10
20
30
40
50
60
0-3 (465) 3-6 (489) 6-10 (471) 10-15 (353) >15 (228)
High Medium Low No Lique.
Liquefaction opportunityLiquefaction Opportunity (%)
0
10
20
30
40
50
60
High Medium Low No Lique.
0-3 m (465) 3-6 m (489) 6-10 m (471)
10-15 m (353) >15 m (228)
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Cyclic Stress Ratio (CSR)
The Cyclic Stress Ratio (CSR) is a measure of the
shear stress that a soil feels during a seismic
event.
CSR = 0.65(amax/g)(v0/v0)rd
amax Peak ground accn., g Accn. due to gravity
v0 In-situ overburden pressure
v0 Effective overburden pressure
rd Stress reduction factor (
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Evaluation of Liquefaction
The Factor of Safety (FS) for liquefaction ofa cohesionless soil deposit is typicallydefined as;
FS = CRR / CSR
where,
CRR = cyclic resistance ratio, andCSR = cyclic stress ratio.
CSR vs SPT-N
Nonliquefying zone
Liquefying zone
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Gwt_2004.shp0-210-202-520-405-10> 40
Fs-0-3m.dbf# 0.1 - 0.5# 0.5 - 0.8# 0.81 - 1# 1.05 - 10
0 20 40 Kilometers
N
EW
S
Factor of safety (0-3m)
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Gwt_2004.shp0-210-202-520-40
5-10> 40
Fs-3-6m.dbf# 0.1 - 0.5# 0.51 - 0.8# 0.81 - 1# 1.05 - 10
9 0 9 18 27 36 Kilometers
N
EW
S
Factor of safety (3-6m)
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Gwt_2004.shp0-210-202-520-405-10> 40
Fs-6-10m.dbf# 0.1 - 0.5# 0.51 - 0.8# 0.81 - 1# 1.05 - 10
0 9 18 27 36 45 Kilometers
N
EW
S
Factor of safety (6-10m)
Conclusions
Trans-Yamuna area of Delhi is proneto liquefaction damage (based onM7.2 EQ.)
>80% of the soil have potential toliquefy
Geotechnical/Geophysical
investigation up to 30 m depth haveto undertaken