Naturally deposited gravelly soils that liquefied following the 2008 wenchuan earthquake, china

The 2008 Mw7.9 Wenchuan, earthquake caused naturally deposited gravelly soils to liquefy over a wide area. Although liquefaction of gravely soils is recognized by the geotechnical profession, observations of liquefaction and non-liquefaction case histories within the literature are few. Through several years of systematic study following the 2008 Wenchuan earthquake (Mw=7.9), 92 locations of gravel liquefaction were identified, described and mapped. These locations lie within an approximately 3000 km 2 area of the Chengdu Plain. Grain size analyses indicates that the ejecta was much finer than the gravels that liquefied. Gravel contents of liquefied soils ranged from 5% to more than 85%. The liquefied gravelly soils were loose, but their measured shear-wave velocities range from 133m/s to 267m/s, with corrected values ranging from 154m/s to 314m/s. The unique depositional conditions under Chengdu Plain provide favorable conditions for extensive liquefaction of gravelly soils. Supplementing to CYY-formula (Cao-Youd-Yuan) (2013), two hydraulic additional requirements as indicating by the dataset of evaluating gravel liquefaction: the soil cap at least 0.5 m thick and an unsaturated zone between the base of the capping soil and the top of the water table should not longer than 2.0 m thick.