Research On Mechanical Effect Of Support And Surrounding Rock Mass Of Soil-Rock Mixtures Backfill Tunnel Under Rainfall Infiltration

In the western region of China,there are many plateaus,hills and mountains,the way of "exploded hill and filled valley" are widely used in the process of large scale urban ground construction.In the process of development and utilization of underground space in urban areas,it is not uncommon for engineering to pass through the backfill area.Rock block backfill is very porous and the pore is large,there is abundant rain in Chongqing area,the new rock block backfill tunnel is under the long influence of rainwater,rainwater infiltration cause rock weight increase and settlement increases,supporting structure deformation and cracking,the tunnel seepage is serious,affect the overall stability of the tunnel,which increases the difficulty and cost of construction.This paper relies on the tunnel across the backfill section of Shangwan RoadHuanshan Park of Chongqing rail transit line ten.Through laboratory test,field test and numerical analysis methods,systematically study the influence law of rainfall infiltration on rock block backfill tunnel surrounding rock deformation and support structure.The main research contents and results are as follows:(1)Through the basic physical index test on rock block backfill,get the density and gradation characteristics of rock block backfill;carry out on-site pumping test,get the permeability coefficient of rock block backfill,and the calculation formula of permeability coefficient of rock block backfill with different rock conten is calibrated;carry out large saturation three axle shear test,study on the stress-strain characteristics of the rock block backfill,the formula of strength parameters change with rock block content is proposed,revise the Moore-Kulun shear strength formula,get the revised strength formula of saturated rock block backfill.(2)Carry out the in-site monitoring test at the relying on rock block backfill tunnel,reveal the tunnel vault subsidence variation and surface subsidence,analyze the surrounding rock deformation characteristics of rock block backfill tunnel;draw shoring structure stress time history curves,analyze the mechanical characteristics of supporting structure in rock block backfill tunnel.(3)Based on the unsaturated seepage theory,using FLAC flow calculation module,analyze the distribution characteristics of stress field and displacement field of the surrounding rock under the heavy rain condition,summarize the variation law of internal force of anchor bolt,initial support and second lining structure,and the results are compared with the field monitoring test results.The results show that the influence of rainstorm on the stress field and displacement field of surrounding rock is mainly reflected in the direction of y.Under the rainstorm condition,the deformation of surrounding rock and the stress level of supporting structure are obviously improved.(4)Based on the finite difference method,the different rainfall intensity and rainfall duration condition are calculated,analyze the effects of different rainfall conditions on the deformation of surrounding rock and the supporting force of the rock block backfill tunnel,determine the most unfavorable rainfall conditions;further explore the influence law of the most unfavorable rainfall condition on rock block backfill tunnel with different rock content,the most dangerous rock content under the most unfavorable rainfall conditions is summarized.The results show that the influence of the deformation of the surrounding rock and supporting internal force of rainfall parameters significantly,considering the surrounding rock deformation,the axial force of bolt and shotcrete lining with two internal force variation,high intensity,short duration condition is the most unfavorable rainfall conditions;the most unfavorable rainfall conditions,less than 40% of the content of stone stone backfill soil tunnel relatively more dangerous.