The World's Largest Naturally Deposited Gravelly Soils Liquefaction Caused by the Wenchuan Ms 8.0 Earthquake

摘要

The 2008 Wenchuan M_s 8.0 earthquake caused extensive naturally deposited gravelly soils liquefied. The merit of the observation overwhelms the engineering point of view of gravel as non-liquefiable soil, and greatly enriches archiving field cases of gravel liquefaction worldwide. Though years of systematical studies, we mapped the 92 identified gravelly soils liquefied zones (sites) as sporadically lay in an area of more than 3000 km~2 in Chengdu Plain. The gravel contents (G_c-values) of liquefied gravelly soils range from 5% to 85% or even larger. The liquefied gravelly soils are loose, but their measured shear-wave velocities (V_s) start from 133 m/s to 267 m/s, and are corrected to 154 m/s to 314 m/s. The PGA-values are predicted from 0.15 g to 0.49 g at liquefied gravelly sites. The shallow soil structure under Chengdu Plain basically consists of an impermeable capped layer and underlain gravelly soils ranging from meters to hundred meters, which provides a fundamental interpretation for gravelly soils liquefaction. A minimum ground shaking of PGA 0.15 g is essential to trigger natural gravelly soils liquefaction, yet massive gravelly soils liquefaction requires 0.20 g to 0.40 g of ground shaking intensity.