An Experimental Study On The Fracture Propagation Model Of Synsedimentary Ground Fissures In Interbedded Sands And Clays

Ground fissure is a geological phenomenon that the rock mass rupture under the action of natural or human factors,and the cracks of a certain length and width are formed on the ground.It is a new and independent type of geological disaster,which have occurred in many countries,among which the Fenwei Basin,North China area and Suxichang area are more serious.The growing of ground fractures becomes a great hazard to the construction and people's lives.In the field investigation of ground fractures,it was found that the common ground fissures developed in some areas exhibited the characteristics of syndepositional structure.Therefore,this article relies on the Natural Science Foundation project “research on the mechanism and effect of ground fissure fracture expansion under csyngenetic Sedimentation”,taking synsedimentary ground fissures in interbedded sands-clays as the research object,and on the basis of identifying the development characteristics of ground fissures rupture expansion,carry out physical model tests of ground fissure propagating and expanding,and use PFC2 D to perform numerical simulation to reveal the process and characteristics of syndepositional ground fissure in interbedded sands-clays,and provide important theoretical support for effective prevention and control of ground fissure disaster.The main conclusions of this article are as follows:(1)Through a lot of literature research and field investigation,it is revealed that the syndepositional ground fissure has typical characteristics of the stratigraphic fault increase with the increase of stratum depth in different strata and the thickness of the stratum in the same stratum is larger in the rising plate.(2)Through physical model test research,it is found that the propagating and expanding of ground fissures in a single sedimentary layer is basically the same as that of non-synchronized sediments.Tension and shear cracks are mainly generated in soil fractures.According to characteristics of the fracture propagation,the tension cracks is divided into vertical cracks and anti-dipping cracks.Vertical cracks start to expand from the surface of the strata.and in the process of extending to the depth of the strata,they have the tendency to form the same angle of dip as the preset hidden fractures.The anti-tilt fractures occur at the tip of the preset fractures,with the reverse tendency of the preset crack inclination to expandto the surface.Shear cracks are usually generated in the intermediate soil between the top of the preset crack and the end of the vertical crack,which tend to have the same inclination as the preset crack,and can penetrate the vertical crack and the preset crack.Under the syngenetic sedimentation,with the coverage of the new sedimentary layer,the anti-dip cracks formed by the underlying sedimentary layer is closed,and it will not expand again when the ground fissure activity occurs again.The new sedimentary layer regenerates vertical cracks and anti-dip cracks when the ground fissures are active.The beginning of the anti-dip cracks extends from the tip of the vertical cracks formed by the overlying sedimentary layer.The vertical fractures penetrate through the through crack by shear fractures,and the through crack(that is,the tops of vertically stretched fractures)formed by the underlying strata.Finally,the ground fissures extended and expanded upward under the syngenetic sedimentation.In addition,through the monitoring of the change characteristics of soil rupture in the model plane and section,stress and strain,it was found that the influence range of ground fissures increased with the increase of sediment thickness.(3)Through numerical simulation experiments,it is found that the characteristics of soil fracture under the syngenetic sedimentation are basically consistent with the results of the physical model test.The new anti-dipping cracks begin to extend from the tip of the vertical crack formed by the underlying sediment layer,and anti-dipping formed by the underlying sediment layer close and will not break again with the ground fissure activity.In addition,the experimental results also show that the upward fracture propagation of ground fractures under the syngenetic sedimentation will still follow the direction of their own tendency.