Model Test Study On Joint Leakage Of Shield Tunnel In Water-Rich Stratum

In order to solve the problem of joint leakage in shallow buried shield tunnel in water-rich stratum,combined with the geological conditions of Hainan,a set of test equipment which can control the leakage position and pressure head was adopted,and several groups of model tests were carried out in sand and clay strata.By analyzing the amount of leakage,the grade of leakage,the formation settlement and the formation stress,the influence laws of leakage on the displacement field and stress field of the surrounding rock were explored.The settlement zones of surrounding rock under seepage at different joint positions of sand stratum was studied.The influence of seepage on surrounding rock was analyzed by scanning electron microscopy.The main conclusions are as follows.The test process can be divided into initial stage,soil leakage stage and convergence stage.In the convergence stage,there is no more soil leakage in the tunnel,only water leakage.The settling tanks of the sand stratum are V-shaped,while the clay stratum have no obvious settling tanks.The leakage and surface settlement of saturated sand tests are much greater than those of saturated clay tests.When the leakage position is the arch springing and the pressure head is 3.1 times of the tunnel diameter,the surface settlement of sandy soil stratum is 57 times of that of clay stratum.The maximum surface settlement is positively related to the buried depth of the leak and the pressure head.In clay strata,when the pressure head increment is the same,the shallower the buried depth of the leakage seam,the larger the surface settlement increment when leakage occurs.In the initial stage,the pore quantity and average pore diameter of the soil samples near the leakage seam are small.In the soil leakage stage,the soil particles near the joints are the first to lose,and the coarse particles begin to gather at the leakage joints and gradually form the soil skeleton,which produces resistance to the migration of fine particles.In the convergence stage,the stable soil arch has been formed,the pore quantity and average pore diameter of the soil sample beside the leakage seam are large,the fine particles adhere to the surface of the coarse particles,and the particles contact and squeeze each other,so that the soil skeleton is more dense.The pore water pressure and earth pressure in the soil leakage stage are the smallest,and the pore water pressure and earth pressure in the convergence stage are larger than the soil leakage and water leakage stage but smaller than the initial stage.The stress loss rate of the surrounding rock at the leakage joint is the largest,and the farther away from the leakage joint,the smaller the stress loss rate.The pore water pressure loss rate is positively correlated with the buried depth of the leakage seam,and the earth pressure loss rate is positively correlated with the buried depth of the leakage seam and the pressure head.In the sand stratum,the earth pressure is not sensitive to the increase of pressure water head.When the pressure water head is increased by 1 times the tunnel diameter,the increment of earth pressure loss rate does not exceed 1.90%.During the test,the effective stress is positively correlated with the buried depth of the leak,and the hydraulic gradient in the convergence stage is positively correlated with the pressure head.In the convergence stage,only the average effective principal stress of arch springing in the saturated sand test exceeds the initial stage level,and the average effective principal stress of crown,spandrel and arch springing in the saturated clay tests exceed the initial stage level.In the sand stratum,the tunnel surrounding rock settlement is divided into erosion zone,displacement zone and stable zone according to the movement characteristics of soil particles.After the offset correction and curve correction,the horizontal length of erosion zone and displacement zone is positively correlated with the pressure head and the buried depth of leakage.When the pressure head is increased by 1 times the tunnel diamete,the growth rate of the erosion zone in the arch springing is 44.64%,while that in the crown is only 18.27%.With the increase of the buried depth of the leakage,the morphology of the erosion zone and displacement zone gradually changed from "horizontal duck egg" to "vertical duck egg".