DISCUSSIONS ON POSSIBLE CAUSES OF THE FORMATION OF MORE THAN FIFTY GROUND COLLAPSE PITS IN ANXIAN COUNTY IN FRONT OF LONGMENSHAN AFTER THE 5.12 WENCHUAN EARTHQUAKE
Yao Xin · 2008
More than fifty ground collapse pits were formed in succession about 20 days after the 5.12 Wenchuan Great Earthquake.They were in Lijiayuanzhi village at the southeastern of Anchang town,Anxian county in front of Longmen Shan.This paper analyzes the possible reasons of the pit formation using the properties of strata,rock,groundwater,erosion and topsoil.Primarily,it was the pre-condition that the calcareous cemented sandy conglomerate of Jurassic period presented below the ground surface.The rock collapse and excess pore water pressure caused by serious seismic ground motion were the start-up factors.Aftershocks resulted in the emergence and development of soil holes.Furthermore,groundwater change accelerated this process.Last,the soil engineering properties determined the shape of the pits.At the same time,this paper also pays attention to other possible reasons including buried fault activity and soil particle loss due to groundwater flow.The paper presents the relavant background evidences.It is desirable that this paper would bring some innovative ideas to find out the real reasons of the pit formation.