Study On Development Characteristics And Genesis Mechanism Of Ground Fissures In Dacheng,hebei Province

Dacheng city is located in the south-central area of the Hebei Plain,the transitional section between the Jizhong depression and the Cangxian fault uplift.Since the Quaternary,due to the strong neotectonic activity,frequent earthquakes,frequent human engineering activities and other factors in the region,ground fissures have become the main geological disasters in Dacheng County,which has caused serious impact on the production activities and life safety of local people.Therefore,in order to reveal the cause of formation and development mechanism of ground fissures in Dacheng County,this thesis analyzes and summarizes the plane distribution characteristics and profile shape characteristics of ground fissures in the study area on the basis of field investigation,excavation of exploration trench and engineering drilling,and makes a preliminary judgment on the development and fracture process of cracks in the study area through similar simulation test and numerical simulation,and summarizes the formation mechanism of ground fissures in Dacheng County,The following are the main conclusions of this thesis:(1)Field survey shows that the ground fissures in the study area are concentrated in Quancun Town and Litan Town in the south of Dacheng County.The ground fissures are mainly in the northeast direction in strike,and have periodic characteristics in time,with a cycle of about 3-5 years.The ground fissures are concentrated on the surface in July and August every year,and have long-term activity.(2)The results of similar simulation test show that the main crack and secondary crack will occur in the process of soil fracture,and the crack initiation position is located near the fault,extending from top to top.There is obvious settlement at the surface soil corresponding to the main crack,and the distance from the main crack is different,so is the settlement and thinning amount of the soil.The closer to the main crack,the greater the settlement and thinning amount of the soil.The farther away from the main crack,the smaller the settlement and thinning amount of the soil.(3)The numerical simulation results show that the vertical displacement and vertical stress of the model at the fault change greatly after the earthquake activity starts,and the model is affected by the tensile stress environment as a whole,which provides a dynamic source for the development of ground fissures.(4)The formation of ground fissures in the study area is closely related to the regional tectonic stress field,fault activity,seismic activity and groundwater dynamic factors.The regional tectonic stress field provides the environment for the formation of ground fissures.Fault activity controls the initial development of ground fissures,seismic activity intensifies the scale and depth of the fissures,and the exploitation of groundwater accelerates the development of the fissures,and finally exposes the ground fissures to the surface.The genesis mode of ground fissures is: fault control-earthquake opening-pumping intensification.There are 26 figures,8 tables and 82 references in this thesi.