A liquefaction case study of gently sloping gravelly soil deposits in the near-fault region of the 2008 Mw7.9 Wenchuan earthquake.

The 2008 M_w7.9 Wenchuan earthquake in China caused widespread soil liquefaction and ground failures. A liquefaction case study of gently sloping ground at Yingxiu Town in the near-fault region is presented, which features its relatively thick deposits of sand-gravel mixtures, high soil stiffness, extremely intensive ground motion, large lateral spreading and severe damage of superstructure. The details of ground motion, site condition, field manifestations of liquefaction, subsurface soil profiles and field testing of shear wave velocities are presented. A conceptual binary mixture model is proposed to explain the gravel content effect on the stiffness and liquefaction resistance of gravelly soils. A preliminary liquefaction triggering evaluation method for gravelly soils is proposed by considering the gravel content correction of shear wave velocities based on the existing simplified procedure for typical sandy soils. The failure mechanism of the Baihua Bridge built at this site is explored, and the liquefaction-induced lateral spreading in down-slope direction might aggravate the failure process by imposing a large kinematic load on the piers besides the inertial forces transferred from the superstructure. [ABSTRACT FROM AUTHOR]