Time-dependent Variation Of Earth Pressure For Unloading Structure Of High-filled Cut-and-cover Tunnel

Due to the special topographical conditions in the western region,a lot of high-backfilled open-hole structures have appeared,and there are few reports on the earth pressure characteristics around high-filled open-holes considering time effects.In this paper,through the finite difference software FLAC3 D numerical simulation,considering the creep performance of the backfill material,the change law of the earth pressure around the high-filled open hole before and after load reduction is analyzed,and the factors(groove width ratio and edge)that affect the soil pressure around the open hole are analyzed.Slope angle),the main research contents and conclusions are as follows:(1)By summarizing and analyzing the rheological characteristics of rock and soil and the development process of creep model of rock and soil,it is determined that the backfill material uses Burgers model.According to the strain-time relationship curve obtained by the creep test,the Origin model software was used to fit the four model parameter values ??of the backfill under different consolidation pressures.(2)The FLAC3 D software was used to establish a numerical model of the original model with a slot width ratio of 1 and a slope angle of 70°.Considering the creep time of 8000 days,the creep calculation analysis shows that the creep effect mainly occurs in the first 2000 In the sky,the earth pressure of each layer of filler above the Myeongdong experienced a linear increase with the creep time—decreased growth rate—and eventually stabilized in three stages.(3)The purpose of load shedding is achieved by backfilling the low-compacted backfill at the top of the Myeongdong cave,that is,low-pressure solid soil.The two different backfill materials were used to compare and analyze the change law of earth pressure after the completion of creep.The calculation results show that: with different backfill materials,the distribution law of earth pressure around the open hole after creep stabilization is very different.(4)Establish a numerical model of unreduced load tunnels with a slope angle of 70°,a slot width ratio of 1,1.5,2,3 and a slot width ratio of 1,and a slope angle of 40°,50°,70°,and 90°.Through calculation and analysis,it is found that the change of the groove width ratio and the slope angle when the creep is stable no longer causes the change of the filling earth pressure.(5)Respectively establish the numerical model of the load-reducing open hole with slope angle 70°,groove width ratio 1.5,2,3,4 and groove width ratio 2,slope angle 40°,50°,70°,90°.The calculation results show that: when a kind of soil considering creep is used as the backfill,the influence of the groove width ratio and the slope angle on the earth pressure of each layer of the load-reducing open-hole filler will disappear with the stability of the filler creep;When the gravel without considering creep is used as the backfill,the influence of the groove width ratio and the slope angle on the earth pressure around the open hole will not disappear with the completion of the low pressure solid soil creep.When the creep is completed,the soil pressure on the top and bottom of the cave is reduced compared with before the creep,and the effect of low-pressure solid soil load reduction is more obvious than before the creep.