DISCUSSIONS ON POSSIBLE CAUSES OF THE FORMATION OF MORE THAN FIFTY GROUND COLLAPSE PITS IN ANXIAN COUNTY IN FRONT OF LONGMENSHAN AFTER THE 5. 12WENCHUAN EARTHQUAKE

Mo re than fifty ground co llapse pits w ere formed in succession about 20 days after the 5. 12 Wen chuan Great E arthquake. They w ere in Lijiayuanzh i v illage at the southeastern o fAnchang town, Anx ian county in front o f Longmen Shan. This paper ana lyzes the possib le reasons o f the p it fo rmation using the propert ies o f strata, rock, g roundw ater, erosion and topso i.l Primarily, it w as the pre- cond ition that the ca lcareous cemented sandy cong lom erate of Jurassic period presented below the g round surface. The rock co llapse and excess porew ater pres sure caused by serious seism ic groundmo tion w ere the start- up factors. A ftershocks resu lted in the emergence and deve lopment of so il holes. Furthermore, groundw ater change acce lerated th is process. Las,t the soil eng ineering properties determ ined the shape o f the pits. A t the same t ime, this paper a lso pays attent ion to other possible rea sons inc lud ing buried fault activ ity and soil particle loss due to groundw ater flow. The paper presents the relavant background evidences. It is desirab le that th is paperwould bring some innovative ideas to find out the real reasons of the p it format ion.