Research On The Construction Control Parameter And Reinforcement Scheme Of Shield Tunneling Initial Underpass Pipeline Group Based On 3D Discrete Continuous Coupling Method

In recent years,with the improvement of the localization rate of shield equipment and the improvement of supporting technology,shield method is widely used in urban subway tunnel engineering.Due to the complexity of geological conditions and the interaction of underground structures,shield tunneling will inevitably disturb the surrounding environment.For tunnels in sandy soil,pebble soil and other special strata,shield tunneling will change the stress state of the soil around the face,and then cause disturbance to the soil within a certain range.When the tunnel depth is shallow and the cohesion of the soil is low,the soil disturbance caused by shield tunneling will quickly transfer to the surface,and also cause adverse effects on underground pipelines and other structures.When the soil displacement exceeds a certain limit,the adjacent structures will tilt or the pipelines in the ground will twist,resulting in a series of environmental effects.On the other hand,the launching and receiving of shield tunnel are often accompanied by the problems of ultra shallow burial and poor stability of excavation face.If the shield tunnel is launching,it is very important to optimize the construction control parameters and adopt reasonable reinforcement scheme to reduce the settlement of underground pipeline caused by shield tunnel excavation.Based on the project of shield tunnel initial underpass pipeline group in sandy cobble stratum of Chengdu metro line 17,this paper studies the construction control parameters and reinforcement scheme of shield tunnel initial underpass pipeline group by using the methods of literature retrieval,theoretical analysis,numerical simulation and field test.1.Through the combination of literature research and numerical simulation,the transfer mechanism of particle motion in PFC particle discrete element is explained,the coupling effect of different coupling methods under gravity is studied,and the coupling quality of various coupling methods is evaluated by the gravity balance effect of the model under self weight.2.By using the method of data investigation and theoretical analysis,the pipeline control standards and control indicators of major cities in China are summarized.According to the requirements of existing codes,the calculation method of axial additional stress and maximum allowable settlement deformation of steel pipeline is proposed.3.The micro contact parameters of particles are calibrated by the method of data investigation and numerical simulation;The calculation method of reasonable time step of complex model is proposed;The settlement variation of pipeline and ground surface under the influence of different tunneling parameters of shield machine is revealed;The necessity of pipeline suspension in shield tunneling is analyzed.4.The statistical analysis of control parameters in shield tunneling construction proves the possibility of using discrete continuous coupling method to simulate shield tunneling parameters;The rationality of pipeline suspension protection scheme is verified.