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“5·12”汶川地震20余天后,在四川省安县的安昌镇东南的李家院子村附近陆续出现了几十个地表塌陷坑并持续扩大。本文以李家院子地表塌陷坑群为研究对象,根据其所在的地层、岩性、地下水、溶蚀作用和上覆土体的工程地质特性定性的探讨了该塌陷坑群的成因。初步认定钙质胶结砂砾基岩的存在是地表塌陷的先决条件;强烈的地震动导致基岩岩体碎裂、解体、塌陷、并压密,同时出现超孔隙水压力,这使上层土体失去支持并开始启动塌陷;余震的地震振动荷载作用导致地下土洞的形成和发展,地下水的变化起到加速作用;上覆土体的工程地质特性决定了塌陷坑在地表的浑圆形状。同时本文也注意到机械溶蚀和隐伏断层活动两种诱导因素的可能,并简要阐述了相关背景依据。
After more than 20 days of the May 12 Wenchuan earthquake, dozens of surface subsidence cranes continued to emerge in the vicinity of Lijiayuanzi Village, southeast of Anchang Town, An County, Sichuan Province. In this paper, the ground subsidence crater group in Lijiayuanzi is taken as the research object. According to its formation, lithology, groundwater, dissolution and the engineering geology characteristics of the overlying soil, the cause of the crater group is discussed. It is preliminarily determined that the existence of calcareous cemented gravel bedrock is a precondition of surface subsidence. The strong ground motion causes the bedrock body to disintegrate, disintegrate, collapse and compaction, meanwhile, the excess pore water pressure appears, which makes the upper soil lose Support and start the collapse. The aftershock seismic vibration loading leads to the formation and development of underground earth caves and the acceleration of groundwater changes. The engineering geological characteristics of the overlying soil determine the round shape of the earth craters. At the same time, this paper also notices the possibility of two inducing factors of mechanical dissolution and hidden fault activity, and briefly expounds the related background.