The Study For Assessment Of Susceptibility To Soil Liquefaction In Taiwan

Taichung, Changhua and Yunlin plains are also nearby the seashores, these lands have a high potential of soil liquefaction. Taichung Port and wharf facilities are located in areas susceptible to liquefaction, and have been damaged by liquefaction in 921 Chi-Chi earthquake. On level ground, during and after an earthquake, the flowing pore-water rises quickly enough, it can carry sand particles through cracks up to the surface, where they are deposited in the form of sand volcanoes or sand boils. (Kramer, 1996) The buildings and houses on the abandoned river channel are tilt due to soil liquefaction. These phenomena have been observed around the riverbeds and the fields in the Taichung, Changhua and Yunlin plains.

We used Wang's model to evaluate soil liquefaction. Soil particle size and soil water contents are the two major factors concerning soil liquefaction in this model. The criteria of fraction finer than 0.005mm.15% means that the part of finer than coarse silt particles is not more than Í 15% in the soil. The pedotransfer function can be changed this quantitative criteria to that the soil belongs to coarse texture (sands, loamy sands and sandy loams in USDA soil textural class). By the same way, Liquid Limit(LL) Í 35% also indicates that the soil belong to coarse grained soil. Because the coarse grained soil has a low liquid limit. Natural water content Ê 0.9LL and Liquidity Index Ê 0.75 indicate that the coarse soils have a high water content.

Sands were considered to be the only type of soil susceptible to liquefaction, but liquefaction has also been observed in gravel and silt. (Kramber, 1996) So the different soil texture has the different sensitivity of soil liquefaction. Soil drainage classes can indicate the different levels of soil water contents, which can be used to evaluate the sensitivity of soil liquefaction, too. So in this study, we classified the soil texture classes into five groups and soil drainage classes to four groups, as Table 1. We rated five classes of the soil liquefaction susceptibility for the shallow foundation construction by these two factors. Because the site near the active fault lines has more energy of emitted waves when earthquake occurs, so if the site under the active fault 5 Km buffer zones, the rate increase one class. In this study, we evaluated, classified and mapped the susceptibility of soil liquefaction in disastrous regions based on three categories in soil information. The map was further verified the reliability in earthquake areas. Most of the boundaries of the soil liquefaction susceptibility units match the soil liquefaction regions. The.reliability of the assessment of soil liquefaction susceptibility is very high. The information provided here could be very helpful in the developing plan for evading soil liquefaction hazard.

There are basically three possibilities to reduce liquefaction hazards when designing and constructing new buildings or other structures as bridges, tunnels, and roads. The first possibility is to avoid construction on liquefaction susceptible soils. The maps we drew can be used as a reference to determine the liquefaction susceptibility of a soil. By characterizing the soil at a particular building site according to these criteria one can decide if the site is susceptible to liquefaction and therefore unsuitable for the desired structure. If it is necessary to construct on liquefaction susceptible soil because of space restrictions, favorable location, or other reasons, it may be possible to make the structure liquefaction resistant by designing the foundation elements to resist the effects of liquefaction. The third option involves mitigation of the liquefaction hazards by improving the strength, density, and/or drainage characteristics of the soil. This can be done using a variety of soil improvement techniques. (EERI,1997)

References

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3. EERI 1997. Adopted from www.eeri.org/EQ_Basics
4. Hillel D. 1980. Fundamentals of soil physics., Academic Press, NY., Pp.347-351.
5. Kramber 1996. Adopted from"www.ce.washington.edu/~liquefaction".
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