LIQUIFACTION AND IT’SREMEDIAL MEASUREA MAJOR CAUSE OF

STRUCTURAL FAILURE DURING EARTHQUAKE SUBMITTED BY

SK KAMRUL ALAM ALIAH UNIVERSITY

UNDER THE GUIDANCEOF

Asst.PROF.MOHASIN JAMAL1

Introduction Objectives About Causes Explanation Modes of liquefaction Ground failure resulting from soil liquefaction Effects Case study Analysis references

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CONTENTS

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IntroductionLIQUIFACTION IS A PHENOMENON WHERE IN A MASS OF SOIL LOSSES A LARGE PERCENTAGE OF ITS SHEAR RESISTANCE ,WHEN SUBJECTED TO MONOTONIC,CYCLIC,OR SHOCK LOADING AND FLOWS IN A MANNER RESEMBLING A LIQUID UNTIL THE SHEAR STRESSES ACTING ON THE MASS ARE AS LOW AS THE REDUCED SHEAR RESISTANCE.Liquefaction occurs in cohesionless soil(typically those with a higher content of larger grains such as sand sized)which have water in the pore spaces,and are poorly drained.

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To understand the liquefaction.

The process that causes the soil to collapse and liquefy during an earthquake.

Which soil are most susceptible to this occurrence.

To find out which soils are strong on their own or could be combined with another soil to make it more stable during an earthquake.

OBJECTIVES

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When does it occurs When the effective stress of soil is reduced

to essentially zero,which corresponds to a complete loss of shear strength.

May be initiated by:- Monotonic loadingCyclic loading

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When the seismic waves pass through the soil,the vibrations cause the individual grains in the soil to

Move around and Re-adjust their position The ultimately results in a decrease in volume of

the soil mass as The grains pack more tightly together A reduction in porosity

HOW IT WORKS

Conditions need to be satisfied for liquefaction which are according to seed

Soil type- soils with 50% or more of their grain size in the range 0.02mm to 0.2mm.

Intensity of ground acceleration- greater than 0.10g is required.

Initial confining pressure- increases with c.f.

Duration of shaking- shaking to continue for some time.

Causes of Liquefaction

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Explanation of Liquefaction

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FLOW LIQUEFACTION

QUASI LIQUEFACTION

SAND BOILING

MODES OF LIQUEFACTION

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SAND BOILS LATERAL SPREADS LOSS OF BEARING CAPACITY GROUND SETTLEMENT FAILURE OF RETAINNIG WALL BUOYANT RISE GROUND OSCILLATION FLOW FAILURES OF SLOPES

GROUND FAILURES RESULTING FROM SOIL LIQUEFACTION

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Lateral Spread

Lateral displacement of large superficial blocks of soil as a result of liquefaction of subsurface layerDisplacement occurs in response to combination of gravitational and inertial forces generated by an earthquake Develop on gentle slope (<3 degree) and move forward free face Displaced ground-Break up internally causing fissures, scarps etc in the form of surface failure

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Liquefaction at depth-decouple overlaying soil layer from the underlying ground

Allowing in upper soil to oscillate back and forth and up and down in the form of ground wave

Oscillation accompanied by opening and closing of fissures and fractures of rigid structure (Pavements, Pipelines)

Ground oscillation

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LIQUEFACTION EFFECTS ON DIFFERENT STRUCTURES IN PREVIOUS EARTHQUAKE

The Damage of Sewerage Structureskushiro (Town)

Lifted up manhole and gushed soil during liquefaction Lifted up manhole

Tokachi-oki Earthquake:2003

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The Damage of Embankment Structures

Toyokoro

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CARACAS(1967)

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Lateral spread at Budharmora (Bhuj, 2001)

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Soil Condition

Case Study: Gujrat Earthquake, 2001

S.No. Region Type of Soil

1 Ahmedabad and Surrounding region

Alluvial belt

2 Bhuj and Surrounding region

Silty sand

3 Coastal area (Kandla)

Soft clay

4 South Gujrat Expansive Clay

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Condition of soil before and after earthquake

D vs depth of layer of three section charaterized by predominant period Tp of microseismic vibrations

Relative density (D) of sand with depth before and after earthquake

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Change in density observed Increase in density observed upto 5m depth from ground

surface Decrease in density from 10-15m depth from ground surface Change in density of sand under saturation during vibration

cause for liqufaction and possible reason for large differential settlement at Ahmedabad

Damage in Zone A-Minor, Zone B- Moderate, Zone C- Heavy Direct co-relation between quality of ground, dynamic

characteristics and anticipated consequences of earthquake

OBSERVATION

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1. Cyclic Stress Ratio (CSR) 2.Cyclic Resistance Ratio(CRR)

By Seed & Idriss (1971)

Evaluation of Liquefaction Resistance of soil

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Cyclic Stress Ratio (CSR)CSR = Cyclic Stress Ratio = (cyc /’vo)v , ’v o= total & effective vertical overburden stress a= peak ground surface accel, g =accl due to gravity rd=stress reduction factor.

rd varies with height.

dvmax

cyc rσga0.65τ

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For evaluating CRR test , undisturbed soil sample is required and as the soil samples of site are too disturbed to give meaningful results, as well as the specialized sampling technique is very costly.For this three types of different tests are done –

SPT (Standard penetration test) CPT (Cone penetration test)BPT (Becker penetration test)

Cyclic Resistance Ratio(CRR)

FS=(CRR7.5/CSR)MSF Ka Ko

MSF= Magnitude Scaling FactorKa=Correction factor for sloping ground

Ko=overburden correction factor

Factor of Safety(FS)

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What is soil liquefaction-Alisha Kaplan Soil Liquefaction Evaluation using Deterministic and

Probabilistic Approaches -Shashank Burman and A. Murali Krishna CALIFORNIA STATE SCIENCE FAIR, 2012 PROJECT SUMMARY

- Breann K. Garcia LIQUEFACTION CASE HISTORIES FROM THE WEST COAST OF THE SOUTH

ISLAND, NEW ZEALAND- Kirsti CARR1 and John BERRILL2

A STUDY ON PROBABILISTIC EVALUATION OF SOIL LIQUEFACTION-

Y. Yao Chi* and Li Ting Ou Department of Land Management and Development Chang Jung Christian University www.ce.washington.edu

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REFERENCES

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THANK YOU