| Urban subways have unique advantages in occupying less ground space resources and alleviating traffic congestion.However,in some areas,existing buildings(structures)have high density,complex geological conditions,and comprehensive utilization of underground space,and cross-tunnel projects have sprung up like bamboo shoots after a rain.Cross-tunnels are difficult to construct due to their complex structure,frequent stress conversion,and great mutual influence of tunnel construction.Based on the engineering background of the Qingxiushan Metro Station of Nanning Rail Transit Line 3,this study conducted a study on the stability of surrounding rock and the sensitivity of supporting parameters during the construction of the cross tunnel.The main research contents and conclusions are as follows:(1)Analyzing the site tunnel monitoring data,it is found that the settlement curve of the tunnel vault is mainly in the stage of small settlement-rapid increase stage-slow increase stage-stable convergence stage;when the tunnel face is excavated to the vicinity of the monitoring section,the monitoring The stress of the surrounding rock increases sharply.As the tunnel face is far away from the monitoring section,the stress value tends to stabilize,and the horizontal displacement of the arch waist appears as a lateral displacement to the empty surface of the tunnel.(2)Establish a three-dimensional numerical model of subway station crossing tunnels through finite element numerical analysis software,explore the influence of different construction methods,different step lengths,different construction sequences,and different support timings on the deformation,stress,and plastic zone distribution of surrounding rock,and analyze the simulation results Through comprehensive comparison and analysis,it is concluded that the tunnel project adopts the three-step method,the length of the steps is 4 m,the construction sequence is one(left tunnel-cross channel-right tunnel-inclined escalator tunnel),and the supporting time is one(excavation and Simultaneous support)is the optimal construction plan.Finally,the numerical simulation results and the field monitoring data are compared and analyzed.The deformation trends of the two are basically the same,which verifies the correctness of the model parameters and the rationality of the construction plan.(3)The sensitivity of the tunnel support structure parameters is optimized and analyzed.On the basis of the above research results,by changing the thickness of the shotcrete,the strength of the shotcrete,the length of the bolts,and the lateral spacing of the bolts,the law of different supporting parameters on the displacement,stress and plastic zone distribution of the surrounding rock was studied,and the 350 mm shotcrete was obtained.The thickness of the concrete,the strength of C25 shotcrete,and the length of the anchor rods are 3.5 m and the lateral spacing of the anchor rods is 1 m,which is the most reasonable,which provides an effective reference for the design and construction of the project. |
