| With the acceleration of urbanization,subway tunnel engineering is being carried out on a large scale.At the same time,accidents such as surface cracking and collapse caused by subway construction are common,and more attention has been paid to the stability and risk research of subway tunnel construction.As a high-risk project,the construction of subway tunnel has many characteristics such as large scale,high risk and complex objective conditions,which is affected by many factors such as geological conditions,design factors and construction environment.Stratum defects are highly hidden,which threaten the safety of subway tunnel construction.Under the disturbance of tunnel construction in soil rock composite stratum,the stratum deformation characteristics and stress transfer law are complicated,and the influence of stratum defects on the stability of tunnel construction in soil rock composite stratum is more uncertain.Based on the NSFC project(51978356): Study on catastrophic mechanism of soil rock composite stratum with defects under construction disturbance of subway tunnel,the soil rock composite stratum with defects in Qingdao was taken as engineer background and theoretical analysis,data mining,numerical simulation and model test were adopt to study the instability risk of soil rock composite stratum with defects under the disturbance of subway tunnel construction in this paper.The main conclusions are as follows:(1)Base on the statistics and data analysis of subway tunnel construction accidents in China from 2014 to 2019,117 accident cases were collected,including 53 collapse accidents,which accounted for the largest proportion among all accident types.The risk indexes include tunnel buried depth,surrounding rock grade,construction method,support strength,ground defects,atmospheric precipitation,groundwater,traffic load,construction quality,construction experience and construction management were determined by classifying the risk sources of 53 collapse accidents,which caused the subway tunnel collapsed.(2)The strata deformation law of different tunnel spacing cavities above the tunnel,at the upward oblique direction of tunnel and at the outside of tunnel arch corner were simulated by ABAQUS.The results of numerical simulation show that,when the distance between void and tunnel is fixed,the influence order of void location on tunnel surrounding rock deformation and surface subsidence is as follow: Void at the outside of tunnel arch corner > Void at the upward oblique direction of tunnel > Void above the tunnel.And when the void position is fixed,the influence of the cavity on the surrounding rock deformation gradually decreases,and the stratum deformation caused by tunnel excavation also decreases with the increase of the distance between tunnel and void from 2m,indicating that the construction of the tunnel far away from the stratum cavity will be safer.(3)Tunnel excavation process with voids in soil rock composite stratum was carried out by 2D model test system.The surface subsidence variation rule and stratum failure mode of different tunnel spacing cavities above the tunnel,at the upward oblique direction of tunnel and at the outside of tunnel arch corner were studied.The results of model test shows that the most unfavorable location of tunnel construction is when void is at the outside of tunnel arch corner and the distance between void and tunnel is two meters,and the maximum surface settlement decreases with the increase of the distance between tunnel and void.The model test results are generally in agreement with the numerical simulation results.(4)According to the source of risk points obtained by statistics of accident cases,the risk level of subway tunnel construction was comprehensively evaluated according to the geological condition level,design factor level and construction factor level.Based on the above,a risk rating system of subway tunnel construction was proposed.According to the risk rating system,the Bayesian network structure was established by data sample learning and expert experience method.(5)The accuracy of the Bayesian network structure model was verified by the result prediction and sensitivity analysis function of Netica software.The network model was applied to the subway tunnel project in the current construction,and the risk results consistent with the actual site were obtained,which confirmed the engineering practicability of this model.According to the formation defect factors,the risk control measures were put forward. |
