Study On The Characteristics And Causes Of Ground Fissure In Xianyang Section Of Weihe Fault

The distribution of ground fissures is very extensive,and the Fenwei basin is the most concentrated.The Weihe fault runs across the middle part of the Weihe basin,and develops multiple tensioned ground fissures along the fault margin.The ground fissures in Xianyang section is located on the south of the Weihe fault,and it's disasters exist for a long time.It is of great significance to study the characteristics and causes of the ground fissures in the Xianyang section of Weihe fault.This paper is based on the research project "ground subsidence investigation and causes research in Xianyang",comprehended the development background and structure pattern of the ground fissures in this area by collected a large amount of data from Weihe fault.Secondly,the characteristics of the ground fissures development are explored through the detailed field geological survey of the Xianyang section: analyzed the plane and profile characteristics of the ground fissures in the Xianyang section by means of trenching and drilling,and summed up the sequence activity characteristics of the ground fissures in the Xianyang section of the Weihe fault by comparing with the previous investigation results,and then generalized the relationship in spatial distribution of the ground fissures and the Weihe fault by comparing the characteristics about them,and summarized the inducing mechanism of ground fissures based on the analysis of groundwater monitoring data.Finally,the influence of groundwater extraction on ground settlement is verified through numerical simulation.The main results are as follows:(1)Analyzed the geological background and structural pattern of Weihe fault through the collected data.The Weihe fault is located in the middle of the basin which is the Cenozoic complex graben fault basin between Gushi sunken and Xi'an sunken,and the Xianyang section is located at the hanging wall of the Weihe shovel fault normal fault in Xianli salient,and the tectonic movement of Weihe fault is the main reason of the development of the ground fissures.(2)The relationship about spatial distribution between Weihe fault and the ground fissures in Xianyang section is included the type of "y" and special-shaped "y",and the distribution in plane is related to the left lateral twist liked the goose.(3)The temporal characteristics of the ground fissures in the Xianyang section show that the activity of 1990 s is the strongest,and then gradually weakened and tends to be stable in 21 Century.(4)The spatial activity characteristic of the ground fissures is obvious in deep part faults,but the shallows are mainly horizontal tensile,and the characteristics of vertical dislocations are hard to find.It shows that there are dislocation in early stage about ground fissures,and it had a strong activity,but eventually stabled.Then land subsidence emerged that caused of pumping.(5)It is not development in the whole line about the ground fissures,which mainly developed in the pumping settlement funnel area.In general,it shows the features about the activity is that the west is strong and the east is weak,and the areas that located in the edge of the funnel is the high incidence area of the ground fissures.(6)Through the numerical simulation of the effect of pumping action on ground fissures by FLAC 3D,it is concluded that the effect of pumping shallow water on the formation of ground fissures is slightly larger than that of the deep water,but the subsidence of the funnel center is greatly increased by pumping the deep water.And the ground subsidence caused by pumping the shallow water by two or more wells is almost the same depth as the single well,but the surface subsidence areas and subsidence depth increased significantly.(7)On the basis of the above analysis,it is concluded that the reasons of the ground fissures in the Xianyang section is the resurrection of some old ground cracks under the influence of human activities,and the two is that the soil strain is accumulated to a certain extent under the action of the stress field produced by the regional tectonic setting,and the soil is slowly losing stability after the soil critical fracture strength is reached.The three is the composite ground fissures induced by the transient pumping action under the control of hidden faults.