Behavior Analysis And Simplified Evaluation Of Crossed Tunnels

With the development of underground spaces,metro,underground expressway and variable kind of municipal pipelines were constructed.The intersection point was formed because these tunnels cross each other and form a network.At the intersection point,the load and deformation of the crossed tunnels is complicated due to tunnel-soil-tunnel interaction.It is necessary to pay special attention to the deformation of tunnels under crossing construction due to this complexity.Besides,the long-term performance of crossed tunnels is affected by the adjacent engineering loads as well.At present,the research mainly focuses on the influence of adjacent excavation and the crossing process.But the influence of adjacent engineering loads on crossed tunnel attracts few attention at home and abroad.By using the 3-D numerical analysis method combined with model test,the deformation behavior of crossed tunnel was investigated.Model test was adopted to study the stress and deformation properties and numerical simulation was taken to verify its reliability.Numerical simulation model of interesting tunnel in actual size was built to study the tunnel deformation and its impact factors under surcharge loading.To calculate longitude displacement of crossed tunnel quickly,this paper put up with analytical method to solve this problem.The concluding remarks were summarized as followed:1.Model test and numerical simulation were both used to study the stress and deformation properties of crossed tunnels under surcharge loading.Composite model section simulation model was put forward to simulate the impact of stress and deformation induced by segment joint.This model was characterized as convenient for setting sensor and was able to put for other experiments.This model was used in the experiment to test the deformation and strain of tunnel.The experiment and numerical simulation results both showed that cross nodes in the upper tunnel was influenced badly in longitude displacement and the lower tunnel was influenced badly in the both sides.Features of these two deformation were proved totally different.2.Numerical simulation model of crossed tunnels in actual size was put to do the parameter analysis and study the response mechanism in the nodes of crossed tunnels under surcharge loading.Shell element was adopted to simulate tunnel segment and the contact way was set as tunnelsoil interface.The global stiffness of tunnel structural was equivalent reasonably to study the stress and deformation properties in the cross nodes in crossed tunnels.The simulation results came up with uneven settlement.The settlement of upper tunnel was larger than the lower one.The largest settlement showed up on the center line of surface load.Smallest radius of curvature of upper tunnel was in the position where the largest settlement happens.The smallest radius of curvature of upper tunnel is larger than the lower one.Smallest radius of curvature of lower tunnel was on the both sides of the position where the largest settlement happens.The maximum relative bend of upper tunnel was larger than the lower one and they both showed up on the sides of cross nodes.Because the upper tunnel was buried shallow and was influenced by the surcharge loading more serious.The lower tunnel was manly affected by the upper tunnel so that the minimum radius of curvature showed up on sides of cross nodes.Especially when settlement and minimum radius of curvature was short of the stated value,the maximum relative radius of curvature would exceed the sated value,which means relative radius of curvature was very important.3.A simplified evaluation is conducted to study the longitude displacement calculation of crossed tunnels during load and unload.The coupling effects between tunnel and soil,tunnel and tunnel is considered when Boussinesq and Mindlin method is introduced.Calculation formula of vertical deformation of intersecting tunnels was put forward and can be solved by programming.It has been proved reasonable by experiment and numerical simulation.This simplified evaluation can be used for rapid evaluation and preliminary design of engineering problems.