Experimental Study On Fracture Propagation Model Of Synsedimentary Concealed Ground Fissures In Loess

The investigation and exploration results of ground fissure disasters in Xi'an in recent years show that there are some high-dip hidden ground fissures in this area.The fracture propagation of these hidden ground fissures is synchronized with the sedimentation of strata.In order to explore the law of fracture propagation of buried ground fissures in the same sedimentary loess medium,a series of large-scale physical model tests are designed on the basis of field investigation results,and the physical model test process is simulated by using PFC2 D numerical simulation software.Based on the mutual confirmation of the two,the related mechanical analysis is carried out.The main achievements of this paper are as follows:(1)Summarize the development characteristics of synsedimentary ground fissures in Xi'an area: for the same marker layer on both sides of ground fissures,the thickness of ascending wall is small,the thickness of descending wall is large,the offset of top layer is small,and the offset of bottom layer is large.(2)A set of physical model tests were designed and carried out to simulate the fracture propagation of buried ground fissures in the synsedimentary environment of loess.It is found that vertical cracks and anti-dip cracks are formed in the soil under the same sedimentation effect,and the closure of early cracks and the opening of new cracks are shown in the same sedimentation process.Compared with different sedimentation effects,the same sedimentation effect has a certain weakening effect on the fracture propagation of ground cracks in the soil,and the dip angle of anti-dip cracks tends to increase with the deepening of soil deposits.The surface subsidence of new overlying strata with equal thickness is getting smaller and smaller due to crack activity.(3)Similar numerical simulation tests were carried out for four settling processes of physical model tests.The numerical simulation results show that near-vertical cracks and antidip cracks are formed in the soil,and the newly formed anti-dip cracks are formed on the basis of the pre-vertical cracks.The dip angle increases with the increase of the number of new overlays,which corresponds to the physical model test results.(4)Based on the theory of fracture mechanics,a preliminary mechanical analysis of the variation of the dip angle of ground fissure cracking in the process of co-deposition is carried out,and the calculation formula for determining the maximum influence width of the surface of hidden ground fissures is deduced.