Liquefaction:

A MAJOR CAUSE OF STRUCTURAL FAILURE DURING EARTHQUAKE

Prakash PaudelGraphic Era University

INTRODUCTION

What is liquefaction?

Relation with earthquakes

DEFINITION:

phenomenon where in a mass of

soil loses 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

Soil grains Soil at normal water pressure

Liquefied soil

To understand the this phenomenonsome basics required regarding:

Total stress, Pore water pressure Effective stress

Case Total Pressure

Pore Pressure

Effective Pressure

Figure- 1 475 150 325

Figure- 2 475 250 225

Figure-1 Figure-2

Total stress, Pore water pressure and Effective stress

General Ground Failure Resulting From Soil Liquefaction:

Sand boils

Lateral spreads

Loss of bearing

capacity

Ground settlement

Flow failures of slopes

Ground oscillation

Lateral spread at Budharmora ((Bhuj, 2001)

Loss of bearing strength

Large deformation occur within the soil allowing the structure to settle & tip

e.g., 1964 Niigata earthquake, Japan-Most spectacular bearing failure--Kawangishicho apartment complex, several four story building tipped as much as 60 degree

Chile earthquake 1960 : An island near Valdivia- Mag. 9.5 Large settlements and differential settlements of the

ground surface-Compaction of loose granular soil by EQ

Japan earthquake 1964: Niigata- Mag. 7.5Settlement and tilting of structures-liquefaction of soil

Flow failure

•Most catastrophic ground failure•Lateral displacement of large masses of soil• Mass comprised of completely liquefied soil or blocks of intact material riding on a layer of liquefied soil•Flow develop in loose saturated sand or silts or relatively steep slope (>3 degree)

Liquefaction MitigationSelection of method for site improvement will depend on:

Location, Area,Depth,Volume of soilSoil types, propertiesSite conditionsAnticipated Earthquake loading Structure type and conditionEconomic and social effects of

structureAvailability of necessary materialsAvailability of equipments and skills

Liquefaction Mitigation Techniques:Soil Improvement Methods

Dewatering:-Permanent dewatering systems lower ground

water levels below liquefiable soil strata, thus preventing liquefaction .

Because lowering of water table increases the effective stress in the soil

This alternative also involves an ongoing cost for operating the dewatering systems

stone columns:-Stone columns works like drains

excavation of poor soil:-

Placement of additional fill:-

Densification of soil :-Various methods of

compaction

Smooth Wheeled Roller Sheep foot Roller

Pneumatic Tyred Roller

Grid Roller

 Pad Foot / Tamping Rollers

Dynamic compaction

Vibro compaction

Compaction Grouting

Compaction by pile Driving

Anchored pile :-

Liquefaction Resistant Structures

Deep Foundation Aspects