Evaluation of liquefaction potential of sub soil

8/12/2019 Evaluation of liquefaction potential of sub soil

1/12

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


2/12

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


3/12

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.


4/12

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)


5/12

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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


6/12

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(%)


7/12

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


8/12

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)


9/12

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 (


10/12

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


11/12

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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

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12/12

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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


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

Documents

Evaluation of liquefaction potential of sub soil