estimation of earthquake induced settlements and liquefaction potential in sandy soil

8/14/2019 ESTIMATION OF EARTHQUAKE INDUCED SETTLEMENTS AND LIQUEFACTION POTENTIAL IN SANDY SOIL

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1

ESTIMATION OF EARTHQUAKE

INDUCED SETTLEMENTS AND

LIQUEFACTION POTENTIAL INSANDY SOIL



2

INTRODUCTION

Practical relevance of the topic

Procedure for estimation of earthquake

induced settlement in sandy soil (Lee,2007)

Procedure for estimation of liquefaction

potential (Idriss and Boulanger ,2004)

Summary and conclusions



3

ESTIMATION OF SETTLEMENT (Lee,2007

)

The total settlement, S for a sandy soil

(1)

Where,

Hi = thickness for layer i

εvi = volumetric strain for layer i

n = number of soil layers.

∑=

=n

i

H S vii

1

ε



4

Volumetric strain (Lee,2007 )

εv = 10(N)-0.6

(2)

for

Where,

εv = volumetric strain;

N = SPT value

CSR = Cyclic stress ratio

01.0)( >

N

CSR



5

N

Fig.1.Relationship between volumetric strain and

N

(source: Lee, 2007)



6

Determination of Cyclic stress ratio

MSF g

aCSR d

v

vr /)())(( max

'65.0

σ

σ =

Where,

CSR = cyclic stress ratio

σv = total overburden pressure at the depth considered;

σv’ = effective overburden pressure at the same depth;

amax

= maximum horizontal acceleration at the ground surface;

g = acceleration due to earth’s gravity;

r d

= stress reduction factor; and

MSF = magnitude scaling factor.

(3)



7

Determination of Magnitude scaling factor

MSF = 2.5 - 0.2M (4)

(source: Lee, 2007)Fig.2 Relationship between magnitude scaling factor and M

Where,

M = magnitude of earthquake.



8

Determination of Stress reduction factor (r d)

Loge (r d) = α (z) + β(z) M (5a)

α (z) = -1.102 – 1.126sin{(z/11.73) + 5.133} (5b)

β (z) = 0.106 + 0.118 sin {(z/11.28) + 5.142} (5c)

Where,

z = depth in meters

M = earthquake magnitude

For z > 34m,

r d = 0.12 exp(0.22M) (5)

For z <= 34m,



9

COMPARISON OF PREDICTION BY THE LEE (2007)

METHOD WITH FIELD OBSERVATIONS



10

Tokachi-Oki earthquake, Japan (1968)

Fig.3 Computed distribution of CSR

with depth (source:Lee, 2007 )



Fig.4 Comparison of computed distributions of

volumetric strain with depth (source: Lee,2007)

11



12

Fig.5 Computed distributions of settlement with depth

(source: Lee, 2007)



Fig.6 Comparison of computed and measured Settlements

(source: Lee, 2007)

13



14

Loma Prieta earthquake, San Francisco (1989)

Fig.7 Computed distribution of CSR with depth

(source: Lee, 2007)



15


volumetric strain with depth (source: Lee, 2007)




settlement with depth (source: Lee, 2007)

16



17

Fig.10 Comparison of computed and measured settlements.

(source: Lee, 2007)



18

ESTIMATION OF LIQUEFACTION POTENTIAL

(Idriss and Boulanger ,2004)



CPT BASED SEMI EMPIRICAL METHOD

CSR = exp { (qc /540) + (qc /67)2 – (qc /80)3 + (qc /114)4 -3 } (6)

Where,

qc = CPT tip resistance.

19

(Idriss and Boulanger ,2004)



CPT Tip Resistance qc

Fig.11 CPT-based case histories and recommended relation

for clean sands. (source: Idriss and Boulanger, 2007)

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• Determine the soil characteristics using CPT.

• Determine the CSR value

• Corresponding to the known value of CSR and CPT tipresistance, mark a point in fig.11

• If the point lies below the line of separation

recommended by Idriss and Boulanger (2004), it indicates

that liquefaction is not likely to occur.

Procedure

21



SUMMARY

Effective and simple methods for

estimation of earthquake induced settlement (Lee,2007)

estimation of liquefaction potential (Idriss and Boulanger ,2004)

22



23

CONCLUSIONS

The procedure for estimation of earthquake induced

settlement by Lee,(2007) method is quite simple

Good agreement is obtained between the predicted results

by the approach proposed by Lee (2007) and the measured

results at two sites



CPT provides a continuous record of the penetration

resistance and is less vulnerable to operator error than is

the SPT test. This totally eliminates any missing out of

liquefiable soil layer.

The Idriss and Boulanger (2004) boundary line can be

conveniently used to separate liquefiable and non liquefiable

soils

Contd…

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estimation of earthquake induced settlements and liquefaction potential in sandy soil

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