Study On The Characteristics Of Ground Fissure Development And Surface Deformation And Failure Modes In Longyao,Hebei Province

The development and activities of the ground fissures in Longyao,Hebei Province seriously affect the production and life of the local people,and the intensity of their activities and the degree of disasters are still increasing year by year.Therefore,it is necessary to conduct in-depth investigation,analysis and research on its developmental features and surface damage forms in order to guide the disaster prevention and mitigation work in the ground fissure development zone to guide disaster prevention and mitigation in the development of the ground fissure.Based on the field geological survey and trench excavation,combined with the results of drilling engineering and surface deformation monitoring,the plane spread characteristics,section structure features,geometric motion characteristics and deformation of the building are analyzed.The damage characteristics are analyzed and studied.The two-dimensional numerical model of finite element method is used to analyze the deformation and fracture characteristics of different types of overlying soil layers caused by fault bedrock displacement.The main results achieved are as follows:1.The study area is located in the southern part of the Ningjin fault and the northern part of the fault and the northern part of the fault,which are located at the junction of the two secondary tectonic units in the faulted mountain of Shanxi and the North China.There are more than a dozen active faults including the Longyao fault,and the frequent seismic events reflect the strong modern tectonic activity of the faults in the area.The study area belongs to the Taihang Mountains and the alluvial plains,and the lithology is pebbles and medium.Sand is dominant and water permeability is good.It is precisely under this hydrogeological condition that with the continuous enhancement of human engineering activities,groundwater is seriously over-exploited,which in turn causes land subsidence and accelerates the development of ground fissures.2.Field surveys in the field show that the cumulative length of the Longyao ground fissure is about 35 km.According to the distribution characteristics and the exposed conditions of the ground fissure,it can be divided into three sections: 1)The western section of the ground fissure extends from Zhoucun near the EW to the tiger.It is 12.7km long and the surface is exposed continuously.The section of the ground fissure has the characteristics of normal and left-lateral strike-slip movement.The maximum vertical displacement in the field is 30 cm,the maximum opening amount is 20 cm,and the maximum strike-slip displacement is 10 cm.2)The middle section of the ground fissure extends from the EW direction of the Yanjiazhuang to the east.After the shop horse,it will extend to NE60° and extend to the south of Kaihe Village.It is 10.6km long and the surface is relatively continuous.The section of the ground fissure has the characteristics of left-lateral strike-slip in the west of Dongdianma,and has the characteristics of right-lateral strike-slip in the east of Dongdian.The maximum vertical displacement of the ground fissure segment is 20 cm,the maximum horizontal opening is 15 cm,and the maximum slip displacement is 8cm.3)The eastern section of the ground fissure extends from Renfang from NE60° to the east of Maoerzhai Village,which is about 11.5km long.The exposure is not obvious;and it is mostly in the form of a collapsed pit along the ground fissure zone;the ground fissure surface has not yet determined its specific displacement movement.3.The exploratory and drilling results of the trench project indicate that the Longyao ground fissure can show the following basic features in the section: the ground fissure activity has the same sedimentary characteristics,the fracture profile is inclined to the south,and the fault distance is also increased with the increase of the depth.The increase is also obvious.The thickness of the upper stratum is obviously higher than that of the lower plate.It is proved that the Longyao ground fissure is formed by the continuous expansion of the deep fault.The quantitative calculation of the typical stratigraphic displacement of the stratum reveals that the Xidianzi trench has a left-lateral strike-slip near the surface.The displacement is 8cm,the right-lateral strike-slip displacement of the Dongdian Ma exploration trench is 7.5cm,and the displacement of the stratum on both sides of the crack surface is not obvious,indicating that the recent activity intensity is weak,10 m.There are two obvious abrupt changes in the ground fault distance on the two sides of the following fracture surface,indicating that the fissure activity in this section is heterogeneous,which is very similar to the stick-slip characteristics of the seismogenic fault.4.Investigation on the damage characteristics of surface buildings found that the relationship between the failure mode of the building and the type of damage and the location of the ground fissure and the degree of damage of the building are very close.The failure mode of ground fissures on buildings can be divided into positive bending shear failure mode,upper and lower disk displacement mode,suspended failure mode,and horizontal strike-slip shear failure mode.5.The numerical simulation results show that: 1)under the action of tectonic stress field,the shallow stratum is dominated by horizontal tensile stress,while the deep stratum is dominated by vertical compressive stress;the deep fracture stratum is in compressive stress environment.The positive and negative sliding movement will occur,and the development of the ground fissure will be more likely to occur under the action of the tensile deformation of the shallow soil;2)The process and form of the crack propagation of the overlying clay layer and the sand layer under normal failure Different: Among them,during the process of normal fault and displacement,the deformation of the overlying clay can be divided into four stages: crack upward expansion,surface soil cracking,anti-tilting crack formation and crack penetration;The deformation of the overlying sand can be divided into four stages: crack upward expansion,reverse tendency crack expansion,vertical crack expansion and crack expansion.