DISASTER CHARACTERISTICS AND INFLUENCE FACTORS FOR GROUND FISSURES AT SONGZHUANG VILLAGE IN BEIJING

In recent years, the occurrence of geological fracture disaster has increased at the Beijing Plain. The geological crack disaster accelerates soil erosion and impacts negatively on infrastructure construction in the area. This paper aims to analyze the generation of geological cracks and reduce the potential losses of economy and property. With geological survey, InSAR monitoring, trenching and drilling methods, the spatial characteristics of ground fissures at Shongzhuang Village are investigated. The factors responsible for the ground fissures and the occurrence mechanism are analyzed based on geological structure, lithology and land subsidence. The conclusions are as follows. (1)The ground fissures at Songzhuang Viallge are sourced at Xiaozhong River, extend along the way through the Shuangbutou Village quay, Gouqu Village, Dapang Village, and end at the Pingjiatuan Village. Its influencing length is up to 8.7 kilometers and extends to the NEE direction. The houses, walls and pavements along the fissures have been damaged to varying degree. The affected objects exhibit tensile deformation. (2)Under the influence of tectonics, the thickness of the Quaternary sedimentary strata is different in two sides of the fissures. The difference in regional sedimentary environment leads to the heterogeneity of stratum lithology. Both of them are the important geological background for the formation of the fissures. (3)Nanyuan-Tongxian fault zone, conceals in the lower part of the ground fissure turn out to be a tensional fracture. Although moving under the ground, it provides the geological conditions for the accumulation and transmission of stress for the formation of the fissures. (4)The long-term and excessive exploitation of groundwater resources has changed the stable environment of the soil, and caused the horizontal and vertical deformation of the soil. The two kinds of deformations altogether caused the ground fissure. The superimposed effects of extensional deformation basement, buried fracture and groundwater overexploitation are the causes of horizontally or vertically compression of soils. The tensile stress concentrated zone is formed near the fault zone in the unsaturated zone. When the stress reaches the tensile strength of the soil, a blind crack is formed. The blind crack is extended to the surface due to rain erosion or of phreatic water table going up and developed to geological cracks and beads-like collapses.