Typical case study of liquefaction-induced damage at Songbai village following Wenchuan Earthquake

The serious damage in Songbai village, Deyang, located at the boundary of seismic intensity zone Ⅶ and Ⅷ, is induced significantly by liquefaction following the 2008 Wenchuan Earthquake. The large amount of spouted soils categories, a lot of liquefaction-generated ground fissures and the apparent liquefaction-aggravated damage are the typical features and are worth for further study. The detailed in-situ tests and comparison with the previous liquefaction-induced damage reveal: (1) The actual liquefied soils are gravels and significantly different from the spouted deposits, while most of which are medium and coarse sand. (2) An efficacious filed test method for measuring gravel liquefaction resistance has not been proposed ever before. The Chinese dynamic penetration test (DPT) is strongly recommended for gravel liquefaction evaluation for its simple apparatus, economical test, continuous data acquisition, etc. (3) The abundant ground fissures in Songbai village are generated by gravel liquefaction rather than the raptures or secondary faults. The fundamental conditions for the generation of ground fissures by liquefaction are the flat ground surface (slop less than 3%) and horizontal non-uniform distribution of liquefiable soils. (4) The fundamental conditions for seismic damage mitigation by liquefaction are the thick upper non-liquefiable soils and relativey dense upper non-liquefiable soil cap. The corresponding quantitative assessment method needs to be further studied.