Study On The Mechanism Of Tectonic Ground Fissure In Plain Area Of Beijing

In recent years,the ground fissure activity in the plain area of Beijing has become more frequently,and the ground damage caused by it has become more and more serious.Therefore,it is important to find out the causes and development mechanism of ground fissures in this area,which is of great theoretical and practical significance for disaster prevention and mitigation of ground fissures in Beijing.Based on the previous' studies,this paper conducted a detailed field investigation on the ground fissures in the plains of Beijing,and then analyzed the distribution,development and genesis of ground fissures under the tectonic activity in this area.The main conclusions are as follows:1.Although the distribution of ground fissures in Beijing is wide,but the surface distribution has a certain regularity.The rupture of the fractures are distributed in the vicinity of the faulted funnels.Most of the fractures are distributed in the edge of the subsidence funnel.And most ground fissures are in the form of strip,intermittent extension;along the fracture zone with more development beaded collapse pit;ground cracks with significant three-dimensional activity,but the vertical activity-based.2.The ground fissures in the plain area of Beijing can be divided into structural,overgrowth and other factors,but the tectonic activity plays a dominant role.Among them,the tectonic fractures are mainly Gaolian camp crack zone,Shunyi fractured belt,Fangshan fissure zone and temple volume village ground fissure zone;overgrowth groundwater type ground cracks are mainly Yangcuncun cracks;other factors type ground fissure Changping South New ground crack zone,including the Pinggu ground cracks,Tongzhou ground fissures.3.Numerical simulation results show that:1)Under the action of regional tensile stress,there are obvious displacement and stress and strain concentration in the upper and lower plates of the basement fault,the effect is reachable to the surface,which leads to the deformation and failure of the overlying soil,In addition,due to the existence of fractures,the distribution of shallow surface soils and the stress and strain distribution are complicated,and consequently secondary stress and strain zone are generated locally.These sites also provide tectonic stress field conditions for the development of ground fissures.2)Due to the obvious slippage of the two plates,the stress concentration is obvious at the intersection of the fracture,the end point and the fault.The corresponding soil layers are often deformed and become a dangerous area where the ground fissure is easy to occur.3)Under the action of self-stress,there is an initial plastic deformation belt along the fracture direction due to the difference of the thickness of the upper and lower strata.Under the continuous action of vertical dislocation and horizontal tension,the main plastic deformation begins at the interface between the bedrock and the soil,and increases with the vertical dislocation and the horizontal tension.When the vertical misalignment reaches 0.4 m,the plastic deformation zone appears on the surface,and with the continuous action of vertical dislocation and horizontal stretching,it is continuously extended to the surroundings until the plastic deformation occurs at the interface with the bedrock and the soil with interconnected.The secondary plastic deformation zone is the same as the main deformation zone,but its tendency is opposite to that of the main plastic deformation zone.4)The deformation of the main plastic deformation zone is mainly affected by vertical dislocation and horizontal tension.The vertical dislocation has a greater effect on the main plastic deformation zone,and the secondary plastic deformation zone is mainly affected by the horizontal tension.The deformation strength of the main plastic deformation zone is much greater than that of the surface secondary plastic deformation zone.