Research On Deformational Properties Of Soil And Tunnel Under Condition Of Adjacent Tunnel Leakage

Because of its safety and efficiency,subway has been built and put into operation on a large scale in urban development.In recent years,water leakage and sand leakage in the construction and operation of urban metro shield tunnel have become the main causes of tunnel construction and operation safety accidents.At present,the research on tunnel water leakage and sand leakage is mostly limited to the water leakage of a single tunnel,while the research on tunnel water leakage and sand leakage under the condition of adjacent tunnel is less involved.In this paper,the deformation of stratum and tunnel under the condition of adjacent tunnel is studied by means of large-scale model test,numerical simulation and theoretical analysis,so as to provide a reasonable theoretical basis for scientifically dealing with safety accidents during construction and operation.The main research contents are as follows:A visual model test device of shield tunnel based on adjustable leakage point is designed and a series of tests are carried out.The critical gap width under different leakage positions,tunnel buried depth and surface water level in the condition of sand soil layer close to the tunnel is explored,and the change of sand leakage gradation,soil deformation The changes of pore water pressure and earth pressure are studied.The research shows that in the sandy soil layer,the slight water leakage of the tunnel has little impact on the parallel tunnel with the horizontal clear distance greater than 2D(D is the outer diameter of the tunnel).The critical gap width is greatly affected by the position of the leakage joint in the tunnel cross section,but the tunnel buried depth and surface water level height have little effect on the critical gap width.Under the same leakage width,the leakage of water and sand from the vault and spandrel is the most likely to cause roof fall.After the occurrence of water and sand leakage,the earth pressure near the leakage joint decreases first and then increases.The earth pressure at the arch shoulder decreases by 0.43 k Pa,the earth pressure at the arch waist decreases by 0.71 k Pa,the earth pressure at the arch foot decreases by 0.84 k Pa,and the earth pressure at the arch bottom decreases by 0.21 k Pa.The final shape of the surface settlement trough caused by water and sand leakage at different positions is different in the horizontal plane.The surface settlement trough formed by water and sand leakage at the arch shoulder and arch waist is circular,and the corresponding radius is 2.61D(D is the outer diameter of the tunnel)and 3.33 D respectively;The surface settlement trough formed by water and sand leakage at the arch foot is oval with the long axis parallel to the tunnel centerline,and its corresponding long axis is 3.13 D and short axis length is 2.71D;The surface settlement trough formed by water and sand leakage at the arch bottom is double circular,the two circles are symmetrical about the tunnel centerline,the center distance is 0.80 D,and the radius of both circles is 1.80 D.Numerical simulation is used to analyze the deformation of surrounding soil and tunnel caused by local water leakage in three simple layered stratum(soft-hard stratum,hard-soft stratum,soft-hard-soft stratum)and typical stratum in Tianjin.The results show that there is no obvious change in the range of stratum settlement caused by tunnel water leakage in the soft-hard stratum and the hard-soft stratum from the 7th to the 30 th day,while the range of stratum settlement caused by tunnel water leakage in the softhard-soft stratum has increased significantly from the 7th to the 30 th day,which indicates that the water leakage of the tunnel passing through the confined aquifer must be treated as soon as possible,otherwise it will cause large-scale significant surface subsidence.The stratum settlement depth caused by tunnel water leakage in the softhard stratum is within 1D below the leakage position;The stratum settlement depth caused by tunnel leakage in hard-soft stratum is about the leakage position;In softhard-soft stratum,the stratum settlement depth caused by tunnel water leakage reaches the lowest part of the whole silty sand layer.Water leakage in the tunnel has a significant impact on the bending moment and axial force borne by the segments of the leaky tunnel and parallel tunnel.The peak value of bending moment caused by water leakage at the arch waist increases most obviously.The peak value of positive bending moment of water leakage tunnel and parallel tunnel increases by 10.74% and 6.71% respectively.The peak value of axial force caused by water leakage in the spandrel is the most obvious.The peak value of axial force in leaky tunnel and parallel tunnel increases by28.46% and 15.46% respectively.Based on the calculation results,the recommended design values of bending moment and axial force for double track parallel shield tunnel project in typical stratum in Tianjin are put forward,which can provide reference for engineering practice.