| According to different parts,water and sand leakage can be divided into spiral conveyor gushing,shield tail sealing failure leading to water and sand leakage,and lining joint crack water and sand leakage disasters.The water and sand leakage disasters of shield tunnels in operation mainly occur at the joints of lining and the joints between lining and underground station structure.In this paper,combined with indoor physical test and numerical simulation method,the problem of stratum subsidence induced by water and sand leakage in tunnel lining cracks was taken as the research object,and the fine sand with the particle size of0.075 mm ～ 2mm was taken as the test soil sample,a set of round and rectangular openings were designed,and a set of visual test simulation system for water and sand leakage in underground engineering was designed.The contrastive analysis of the subsidence results of sand layer induced by sand leakage at circular and rectangular opening had conducted,the experimental and numerical simulation research on the sand loss law induced by rectangular opening was carried out.This paper analyzes and summarizes the flow pattern of sand inrush,the stage and characteristics of sand inrush process,the influence of the type of opening on the sand leakage process,the influence of soil thickness on the sand inrush process,and the influence of water flow on the sand loss process.The main conclusions are as follows:(1)When the size of the opening was fixed,with the increase of the thickness – span ratio,no subsidence,subsidence but no sand inrush,sand inrush will occur in turn.Moreover,in the comparison of the experimental group with round and rectangular opening,the vertical subsidence area of columnar shape was first produced in the process of sand inrush,and then the dynamic funnel surface was produced.Finally,the sand leakage continued until the funnel slope was stable and the sand inrush ended.The whole process can be divided into initial stage,induced stage,diffusion stage and stable stage.In addition,the profiles of the funnel shaped subsidence surface induced by circular and rectangular opening can be fitted by quadratic function.The test results show that the shape failure angle of sand inrush was related to the natural angle of repose α,and the difference between θ and α was about 13 °.(2)The amount of sand leakage,the scope of subsidence and whether the sand inrush were independent of the length of the two adjacent sides.The time and speed of sand leakage were related to the length of the two adjacent sides.The larger the difference between the two adjacent sides,the longer the time and the slower the speed of sand leakage.When the rectangular opening was square,the time of sand leakage was the shortest and the speed of sand leakage was the fastest.The area of sand leakage hole was an important factor that affects the severity of sand layer subsidence.Compared with rectangular one,the area of circular one increased faster,which has a greater impact on the process of sand layer collapse.(3)When sandy soil was saturated in liquid,the loss of "water + sand" was different from that of dry sand.Because of water and sand gush out at the same time,the loss amount and loss process time of "water + sand" test were larger than "dry sand" test in the scope of collapse.Because of the constant flow rate,the flow rate keeps the same.It can be seen that the flow rate has nothing to do with the water content,but only with the sand inrush opening.(4)PFC triaxial compression simulation test was used to calibrate the meso-parameters of selected soil samples.The 1:1 numerical model of acrylic bucket was established by using cylindrical surface and trapezoidal surface without upper and lower top surface.The process of sand loss was simulated,and the stress of sand particles in the process of soil collapse and sand burst disaster caused by sand loss was studied.The change of the contact force chain,and the change of the force on both sides of the rectangular opening were studied. |
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