Experimental Study On The Fracture Propagation Of Ground Fissures Under The Action Of Aeolian Syn-sediment

Ground fissures are a common ground deformation disaster,which is widely distributed and has a serious impact on urban construction and citizen's lives.Ground fissures in many areas have the characteristic of syn-sedimentary development,especially Xi'an ground fissures are the most typical.The development process and formation mechanism of syn-sedimentary ground fissures are still unclear.This thesis takes ground fissures under aeolian syn-sedimentation as the research object,carries out physical model experiments of ground fissure rupture and propagation,and uses PFC^2D numerical simulation software to simulate the experiment,so as to summarize the rupture and propagation process of ground fissures under aeolian syn-sedimentation.The main results achieved here are as follows:(1)Take Xi'an ground fissure as an example,the development characteristics of syn-sedimentary ground fissures are summarized,that is,the dislocation amount of the same soil layer on both sides of the fissure increases as the depth increases,and the soil layer thickness of the descending plate of the fissure is greater than that of the ascending plate.(2)In the physical model test,under the effect of aeolian co-sedimentation,two tensile fractures were mainly formed in each sedimentary layer:anti-dip fracture and steep-dip fracture.The steeply dipping cracks spread downwards from the top of the soil and basically penetrated to the bottom of the layer.The starting position of the rupture shifted to the lower wall with the increase of the sedimentary layer,roughly on the pre-determined crack extension line;The anti-dip fractures spread upward along the top of the newly formed steep-dip fractures in the previous sedimentary layer.When the sedimentary layer reaches a certain height,some layers will continue to produce down-dip cracks above and below the anti-dip cracks,thus forming arched cracks.The cracking time of each layer of anti-dipping cracks is basically the same as that of steeply-dipping cracks.The crack propagation is mainly concentrated within 10mm of the descending displacement of the hanging wall.After that,the cracks have basically been penetrated,and the later period is mainly due to cracks widening.(3)In the numerical simulation,the maximum displacement area of the particle displacement in the x-direction under the same sedimentary action is located at the vertical projection of the predetermined fracture on the surface.Its peak value increases with the increase in the settlement of the hanging wall.Steeply inclined cracks are mainly subjected to horizontal tension,and the width of the cracks gradually decreases downward.The area with the largest particle displacement in the y direction is mostly distributed near the steeply inclined fractures of the upper layer,and there is a significant difference between the preset fracture extension line and the two sides of the anti-dip fracture.The underlying soil layer forms a broken zone at the pre-determined crack extension line where the cracks develop.The anti-dip cracks in the new sedimentary layer are mainly stretched in the vertical direction,and the crack width gradually decreases upwards.(4)Based on the results of physical model tests and numerical simulations,the rupture and propagation process of ground fissures under eolian syn-sedimentation is summarized;The influence range of ground fissures is divided into main deformation zone and micro-deformation zone,and the influence width and angle of ground fissures on the upper and lower walls after each period of settlement are counted.