The Mechanism Study Of Strata Subsidence Induced By Sand (Water) Leakage Of Tunnel Lining In Sandy Stratum

In recent years,the rapid development of China’s transport industry,underground space had been more and more extensive development and utilization,tunnel as an important transport medium had been large-scale construction.The formation collapse caused by sand leakage（water）in tunnel lining seriously affects the safe operation of tunnel engineering.In this paper,the collapse mechanism of sandy soil layer induced by sand（water）leakage in tunnel lining was studied by means of laboratory test,theoretical derivation and numerical simulation.The main work and research results were as follows:（1）The visual ground collapse sand leakage（water）laboratory test system was designed by ourselves.Based on the study of the ground collapse induced by sand leakage（water）in the soil layer with different thick-span ratios under the same gusher,it was concluded that the larger the diameter of the lining cavity was,the deeper the burial depth was,and the greater the impact on the ground surface will be.The ground collapse induced by sand leakage at the circular inrush was approximately circular in the plane,and the central section on the facade can be approximately described by quadric surface.The natural repose Angle of soil was numerically equivalent to the internal friction Angle of soil,and the difference between its shape failure Angle and the natural repose Angle was 13°.（2）Through the study of ground collapse induced by sand leakage（water）at different inrush orifices,it was concluded that with the same diameter of the gusher,the soil layer thickness increased,and the rate of sand leakage basically remains unchanged;the sand leakage velocity at inrush orifices with different diameters increases with the increase of the aperture;There was a critical crack ratio condition for sand failure induced by sand leakage in tunnel lining.（3）Based on the analysis of the mechanism of water sand inrush,the influencing factors of inrush of sand were summed up as the size of sand body and the width of water sand channel.The process of water sand inrush was regarded as the process that the infinite cabin discharges the water sand from the channel under hydrodynamic force and self gravity.The concept of critical split grain ratio was proposed.Three kinds of contact interlocking arch models were established,which were linear,symmetrical triangle and arc curve.the formula i_maxfor calculating the critical crack ratio of sand failure was derived by the mechanical model,and it was pointed out that the critical crack ratio of water sand inrush was related to the internal friction angle of soil.（4）Adopt the method of numerical simulation,the bin type crushing sand discrete element model was established,to simulate the collapse of sand sand body under the state flow form,by changing the split ratio and the interparticle friction coefficient,verify the crushing sand disaster under the geological condition,the critical crack ratio of sand was 5.1,with the increase of angle of internal friction of soil it was corresponded critical crack ratio,the greater the grain.By setting the contact stress sensor,the stress peak of lining increases with the increase of crack ratio in the process of sand inrush.