关键词: 地震, 土体液化, 细粒土, 塑性指数, 液化可能性, 准则

Abstract: This paper reviews the characteristics of soil liquefaction-induced damage observed from the Northridge, USA earthquake, 1994, the Hanshin, Japan earthquake, 1995, the Kocaeli, Turkey earthquake, 1999, the Chi-Chi, Taiwan earthquake, 1999, in China, the Wenchuan, China earthquake, 2008, the Maule, Chile Earthquake, 2010, the Darfield and Christchurch, New Zealand earthquake, 2010 to 2011, and the great East Japan earthquake, 2011. There are several characteristics in the occurrence of liquefaction and consequence damage which are different from a number of cases experienced in these earthquakes. These are summed up as follows: (1) The unprecedented long duration of the shaking and extensive makes the occurrence of liquefaction in the newly reclaimed land, fill area is 300~400 km distant from the epicentral area attributed to the rarely encountered huge moment magnitude Mw9.0 earthquake. (2) A number of site liquefactions and lateral spreadings are observed in seismic intensity scales of Ⅴ and Ⅵ, an area of low intensity is attributed to the encountered magnitude scale Ms8.0 and Mw8.8 earthquakes. (3) Severe liquefactions in sites are observed having young alluvial, lacustrine deposits along rivers and sea bay areas, and in reclaimed land, fill area contains fine-grained soils, gravel sands in less than fifty years. (4) Severe liquefaction in natural gravel sand deposits occurs. (5) Soil liquefies in depth of 20 m. (6) Liquefaction and re-liquefaction of the sites over a large region do not result in densification of the loose deposit, future earthquakes of sufficient magnitude can again induce liquefaction. (7) Severe liquefaction occurs in low to moderate plasticity soils containing more than 50% fines content (grain size is, smaller than 0.075 mm) or more than 25% of clay content (grain size is, smaller than 0.005mm), however, field evidence of liquefaction may not be observed in transition behavior fine-grained soils between sand-like and clay-like behaviors. (8) Ground cracking without venting of sand boils is more likely as the depth and thickness of the liquefied layer increases and decreases, respectively; vented material, provided field evidence of liquefaction, may be absent due to the large depth to, and small thickness of, the liquefied layers. There are a number of spectacular case histories of liquefaction of sediments deposited in late Pleistocene time Q3. The clay content is not a reliable index for evaluating between clay-like and sand-like behaviors in a fine-grained soil. Fine-grained soils with the low plasticity index PI and high water content wc are susceptible to liquefaction; the use of the PI and water content to liquid limit ratio wc/LL is a good criterion of liquefaction possibility; for soils. Based on work in progress of the case histories of liquefaction and the results of laboratory tests for fine-grained soils from Boulanger, Idriss, Bray and Sancio, Seed and Cetin et al, a new liquefaction possibility criterion for soils is proposed as follows: soils with PI<12 and wc/LL>0.85 are susceptible to liquefaction; soils with 1220 or wc/LL<0.80 is not susceptible to liquefaction.

Key words: earthquake, soil liquefaction, fine-grained soils, plasticity index, possibility of liquefaction, criteria