The Relationship Between The Development Of The Ground Fissures And The Neotectonic Activities In Beijing Plain

Beijing plain area is located in the North China block in the northern Yanshan fold belt,the two tectonic units in North China fault depression and the intersection.The new tectonic movement is intense in the area,resulting in growth in the area of cracks,and in recent years,over exploitation of groundwater human engineering activity,prompted the development process to accelerate the crack,brings serious harm to the local construction,agricultural production and life of the masses.Therefore,in order to know the characteristics of fracture development zone,analyze its growth mechanism and formation mechanism of the relationship between the crack and the area of new tectonic activity,the ground fissure disaster prevention,reduce the loss of people and property has important significance.This thesis takes Beijing plain area to crack as the object,the basis of previous researches,collect the geological environment characteristics of the study area and combined with field investigation project,summarizes the development and distribution characteristics of the ground fissure,through numerical simulation,the causes of the mainland crack zone and development mechanism are analyzed,and its relationship with neotectonic activity and discusses the.The main results are as follows:1?The plain area of Beijing formation from old to new is relatively complete,since the Cenozoic,in the area of several fault activities make its "two long foldersconcave" and a plurality of secondary fault depression tectonic pattern,strong neotectonic movement caused by fault activity in the region,strong seismic activity,and further cause the study area of ground fissures.2?Field investigation shows that the development of Beijing plain area is mainly zonal distribution,and the overall direction of distribution is NE-NNE and NW-NNW two directions.In addition,there are some cracks in the local section,which are star shaped and flaky,without obvious trend.3?The vast majority of the crack distribution and fracture position closely,cracks in the macro regional development characteristics were generally linear in active fault zone and along the region near the zone,shows that tectonic activity obviously control effect of ground fissures,is a major cause of the ground fissures.4?Numerical simulation results further showed that the close relationship between crustal deformation and ground fissures,and the deformation mechanism according to the mechanical,structural fracture zone can be divided into control and activity of basement faults stretching control type two categories,including:(1)In the study area of the ground fissure fracture rock mass on both sides of the relative motion to cause the deformation response of soil to the upper part of the internal force of fault activity on the surface or access control,belonging to the ground fissures faults of this earth like cracks,mainly characterized by extending well along the fault zone,the obvious characteristics of vertical dislocation.(2)The whole study area is located in the crustal extensional deformation environment,so there is also the basement extension controlled fissure.Under the action of regional extensional tectonic stress field,the crust has the effect of reducing tension and thinning,which results in the whole thinning and rupture of the overlying soil.It is shown that the tensile stress and strain concentration in the surface soil layer occurs in a certain distance of the active fault inflection point,the end point,the fault intersection and the two sides of the fault.