Submitted by

Prateek Vyas

1808/06

C-3

What is soil liquefaction?When has soil liquefaction occurred in the past?Where does soil liquefaction commonly occur?Why does soil liquefaction occur? How can soil liquefaction hazards be reduced?

Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world. Liquefaction occurs in saturated soils.

When liquefaction occurs, the strength of the soil decreases and, the ability of a soil deposit to support foundations for buildings and bridges is reduced as seen in the photo of the overturned apartment complex buildings in Niigata in 1964

Increased water pressure can also trigger landslides and cause the collapse of dams. Lower San Fernando dam suffered an underwater slide during the San Fernando earthquake, 1971

Liquefied soil also exerts higher pressure on retaining walls which can cause them to tilt or slide.

On level ground, the high pore water pressure caused by liquefaction can cause pore water to flow rapidly to the ground surface. These features can often be observed at sites that have been affected by liquefaction, such as in the field along Hwy 98 during the 1979 El Centro earthquake .

Liquefaction has been observed in earthquakes for many years. In fact, written records dating back hundreds and even thousands of years describe earthquake effects that are now known to be associated with liquefaction. Some of those earthquakes are listed .

As a part of the Pacific Ring, the southern coast area of Alaska experiences many earthquakes. On Good Friday, March 27, 1964, a great earthquake of magnitude 9.2 struck Prince William Sound and caused severe damage in the form of landslides and liquefaction

The liquefied seams and lenses disturbed the sensitive clays, and caused their strengths to drop below the levels needed for stability. Here shown road embankment failure.

The October 17, 1989 Loma Prieta earthquake (M=7.1) caused damage not only in the vicinity of the epicenter near Santa Cruz, to the north but also in more distant areas around San Francisco and Oakla.

Soil liquefaction caused major damage to waterfront facilities, structures, and buried pipelines at locations in the Bay Area where loose saturated, sandy soils were susceptible to liquefaction. The numerous sand boils that were observed provided indisputable evidence of the occurrence of liquefaction.

The 1995 Great Hanshin Earthquake (M=6.9), commonly referred to as the Kobe earthquake, was one of the most devastating earthquakes ever to hit Japan; more than 5,500 were killed and over 26,000 injured .

The spectacular collapse of the Hanshin expressway illustrates the effects of the high loads that were imposed on structures in the area. The strong ground motions that led to collapse of the Hanshin Express way also caused severe liquefaction damage.

Liquefaction only occurs in saturated soil. Its effects are most commonly observed in low-lying areas near bodies of water such as rivers, lakes, bays, and oceans.Port and wharf facilities are often located in areas susceptible to liquefaction, and many have been damaged by liquefaction in past earthquakes.

Most ports and wharves have major retaining structures, or quay walls, to allow large ships to moor adjacent to flat cargo handling areas.

To understand liquefaction, it is important to recognize the conditions that exist in a soil deposit before an earthquake.

Observe how small the contact forces are because of the high water pressure. In such cases, the soil will have very little strength, and will behave more like a liquid than a solid - hence, the name "liquefaction".

There are basically three possibilities to reduce liquefaction hazards -:

1. Avoid Liquefaction Susceptible Soils

2. Build Liquefaction Resistant Structures

3. Improve the Soil

There are a number of different ways to evaluate the liquefaction susceptibility of a soil deposit -:

1.Historical criteria

2.Geological criteria

3.Compositional criteria

Fraction finer than 0.005 mm< 15% Liquid Limit, LL < 35% Natural water content > 0.9 LL Liquidity Index < 0.75

A structure that possesses ductility, has the ability to accommodate large deformations . To achieve these features in a building there are various aspects to consider-:

1.Shallow foundation aspect

2.deep foundation aspect

It is important that all foundation elements in a shallow foundation is tied together to make the foundation move or settle uniformly, thus decreasing the amount of shear forces induced in the structural elements resting upon the foundation.

The well-reinforced perimeter and interior wall footings are tied together to enable them to bridge over areas of local settlement and provide better resistance against soil movements

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A stiff foundation mat (below) is a good type of shallow foundation, which can transfer loads from locally liquefied zones to adjacent stronger ground.

This can be achieved by densification of the soil and improvement of its drainage capacity .There are various technique-:

1. Vibroflotation

2. Dynamic Compaction

3. Stone Columns

4. Compaction Pile

5. Compaction Grouting