Research On Formation Collapse Induced By Sand Leakage Of Tunnel Segment Damage

With the continuous increase of urban population in my country,the requirements for strengthening the construction of transportation infrastructure,the shortage of urban space and the contradiction of layout defects have made the development and utilization of underground space an effective means to relieve the pressure of urban traffic,and the construction of subway tunnels has entered an unprecedented high speed.During the development period,the occurrence of stratum collapse accidents caused by sand leakage of tunnel segments caused severe social impact.In this paper,the combination of indoor design test and numerical simulation is used to study the interaction of sand leakage and soil deformation during stratum collapse under different working conditions(length-to-width ratio of leakage opening,soil layer properties,soil thickness,and pebble layer).The main conclusions are as follows:(1)The critical aspect ratio of the rectangular leakage under different geological stratification conditions was determined by the indoor sand leakage test,within a certain aspect ratio range,it was easier to form the arch effect to prevent the continuous occurrence of sand leakage accidents,but when the aspect ratio was less than 1.6,the increase of the soil thickness had no effect on the value.(2)The influence area of collapse induced by the rectangular leak was oval in plane and funnel-shaped in section.The eccentricity was introduced to describe the flatness of the influence area of collapse.This value was related to the aspect ratio of the rectangular leak and the thickness of the soil layer.When the aspect ratio was greater than 3,the eccentricity was inversely proportional to the aspect ratio value,and proportional to the thickness of the soil layer;when the aspect ratio value was less than or equal to 3,the value was infinitely close to 1,and the impact range of the collapse was similar to a perfect circle and no longer affected by soil thickness.(3)The simulation calculation results of PFC3D(2D)software were similar to the results obtained from the sand leakage test.The length-width ratio of the rectangular leakage opening and the thickness of the overlying soil layer were two important factors that affected the formation collapse process.It was easier to form an arch effect within the range to prevent sand leakage accidents from continuing to occur.(4)Based on the double-arch effect,the soil failure was divided into two stages.The first stage was the arch failure stage.The soil forms a slump arch,and the failure process corresponded to the formation and destruction of the slump arch.The second stage was the overall failure stage,and the failure process corresponded to the formation and failure of stress arches.The double-arch effect formed by the combination of slump arch and stress arch could control the development of soil failure process.(5)Monitoring the porosity above the leakage opening and the floor load value under different particle arching forms found in the indoor sand leakage test and numerical simulation,it is found that the porosity of coarse particles mixed into arching is greater than the arching porosity of fine particles,and the porosity is related to the floor load.The fluctuation is more severe,which verifies that the process of arch failure is a process of continuous failure and generation of the slump arch.