Statistics Of Tunnel Shield Excavation Accidents And Numerical Simulation Of Excavation Process

On the basis of existing research by other scholars,this paper collected the data of 297 construction accidents in China's subway tunnels from 2003 to 2018.Through the comparison of shield and non-shield construction accident data,the main characteristics and rules of shield construction accidents are analyzed,and the deformation rule of stratum during tunnel excavation is studied by numerical simulation.The following conclusions can be drawn:(1)In China's subway construction,the average accident incidence per kilometer is 4.4%,and the average accident incidence per kilometer of shield construction is 4%.The three cities with the highest accident incidence are Qingdao(14.7 percent),Guangzhou(12.2 percent)and Changchun(10.4 percent).The average loss rate is 1.02 yuan per 10,000 yuan,and the three cities with the largest loss rate are 6.8 yuan per 10,000 yuan in Foshan,4.37 yuan per 10,000 yuan in Shanghai and 3.12 yuan per 10,000 yuan in Wuhan.The distribution of subway construction accidents in China generally shows a trend of "decreasing gradually from east to west,and decreasing gradually from south to north".(2)The accident incidence of shield construction per kilometer is 4%.Among them,the probability of a general grade accident is 85.47%,a larger grade accident is 12.82%,a major grade accident is 0.85%,and a particularly major grade accident is 0.85%.The probability of collapse accident is 39.32%,mechanical injury accident is 18.8%,gush water accident is 12.82% and high falling accident is 10.26%.On average,1.05 people were killed and 0.6 injured in each accident,resulting in a total economic loss of 2.677 million yuan.(3)Through the numerical simulation of tunnel shield construction process by FLAC3 D software,it is found that the most likely locations for collapse accidents are the beginning of the tunnel,the tunnel excavation face and near the load boundary.The rules of settlement,deformation and distribution of internal forces of the soil under different loads and depth of tunnel are as follows:(1)when the distance between the tunnel and the load is greater than 4 times the diameter of the tunnel,the influence of the load can be ignored;(2)the load will change the development path of settlement curve and the change of surface settlement lags behind that of tunnel excavation;(3)with the increase of buried depth of tunnel,the lateral surface settlement curve from "thin","high" to "short","fat",which increases the influence range,and the amount of deformation at the top and bottom of the tunnel is increasing;(4)there is an obvious "inflection point" at 21 m in the surface settlement curve along the tunnel axis under load.The surface settlement velocity suddenly decreases and remains unchanged in the load area;(5)when the distance between the tunnel and the load is close,the stress concentration phenomenon appears at the underside of the building,the axial force value of the tube segments in the tunnel increases,the shear force diagram and bending moment diagram are no longer continuous,and the internal force value at the load position significantly decreases.