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Some notes on the phenomenon of "Liquefaction"

09/23/2008 3:54 AM

I happened to look on CR4 at a query pertaining to the topic: "Liquefaction".

My experience as a Civil and Foundation Engineer of some repute has taught me the following:

1. The process of "Liquefaction" gets triggered due to the imposition of dynamic and lateral loads - such as those caused by earthquake tremors or shocks.

2. The effect of the process is essentially on the shearing strength of the soil in question.

3. The effect gets felt predominently on cohesion-less soils - sands of medium and low density- such as those alluvial soils. Dense sands are, however, safe as a foundation medium.

4. The result of the process itself is a sudden increase in the excess pore water pressures within the soil grains that exceed the inherent shearing strength of the soil and thus reduce the ability of the soil structure to bear any loads imposed upon it, since its shearing resistance gets to 'nought' = 'zero' (or negative even!)

5. The immediate effect is the imminent collapse of any superstructure that happens to be standing on such a soil that is subjected to "Liquefaction" as explained above.

6. Structural and Foundation engineers are, therefore, cautioned while designing and erecting structures founded on fine to medium sand media, located in active earthquake zones, to take precautions to improve the Relative Density to safe levels by adopting suitable ground improvement measures - so as to withstand the impact of the anticipated dynamic loads prevalent in the region, and avoid damage due to "Liquefaction".

7. A well-designed structure itself may not suffer any damage, but it will literally be collapsed, if ever subjected to "Liquefaction"!

I trust, the above clarifies the issue.

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#1

Re: Some notes on the phenomenon of "Liquefaction"

09/23/2008 4:32 AM

Hello plan

for your short Article.

I cannot give you a GA Point, because your Post is not an answer, but I can give your Topic Points a high Mark, and the

Kind Regards....

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#2

Re: Some notes on the phenomenon of "Liquefaction"

09/23/2008 11:09 PM

I very much appreciate and agree with your explanation of liquefaction and, as a civil engineer, the relation to foundations for buildings etc.

I am more concerned regarding buried tanks that sit on foundations and pipelines during this phenomenon. Building collapse but tanks and buried pipelines can become buoyant and rise to the surface. The relation between satrurated sand overburden and the overburden during liquefaction is interesting. When is the grain size of the sand subject to liquefaction and what is the density of the sand/water mixture during liquefaction?

Appreciate your input.

chama

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#3

Re: Some notes on the phenomenon of "Liquefaction"

09/24/2008 3:15 AM

1. Shearing Strength of the soil medium under "effective stress condition" is the governing factor.

2. Higher the grain size, higher the shearing strength. Hence the preference to coarse grained sands.

3. Pipelines or tanks buried in a trench and encased by well-compacted coarse-grained sand (with a Relative Density of not less than 70%) should be able to withstand the imposed static and dynamic loads, in my opinion.

Thanks for the appreciation of my short notes.

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