| The number of new tunnels passing through existing subway tunnels at close distances is gradually increasing.Certain safety measures are often used in the construction to protect existing tunnels.It is necessary to study the influence mechanism of shield tunneling on existing tunnels and the protective effects of various safety control measures.In this paper,the research work is based on theoretical solutions,supplemented by measured data analysis and numerical simulation.The main research methods,achievements and innovations of this paper are as follows.(1)The influence of the short-distance underpass of the shield on the internal force of the existing tunnel segments was studied.A model of the confining pressure redistribution of the existing tunnel under the additional stress was proposed.The calculation formula for the circumferential confining pressure of the existing tunnel is deduced.The internal force of the lining under the corresponding confining pressure is calculated by using the modified inertia.(2)The influence of the tunnel load on the longitudinal settlement deformation of the tunnel was studied.A cooperative deformation model that comprehensively considered the dislocation and rotation deformation effects between the segment rings and the rotation deformation was adopted.The additional load of the tunnel caused by the pile load was deduced and calculated..Calculate the longitudinal settlement of the tunnel,the shear force between the rings,the amount of dislocation and the turning angle by the principle of minimum potential energy.(3)The effect of the supporting trolley in controlling the deformation of the tunnel in the overlapped section of the tunnel was evaluated.The reinforcement and weight of the supporting trolley were comprehensively considered.In view of the uneven stiffness of the existing tunnel along the longitudinal direction,a calculation model for the vertical deformation of the tunnel with longitudinal non-uniform stiffness is proposed,and the calculation formula for the vertical deformation of the existing tunnel is derived.(4)The influence of the grouting ring of the existing tunnel on the control of the settlement of the existing tunnel is studied.The acceleration reduction effect of the grouting ring in the process of additional stress transmission and the reinforcement of the ring foundation soil are considered.The stress reduction model in the heterogeneous soil layer and the tunnel settlement calculation model are proposed.The calculation formula for stress reduction after passing through the grouting ring is deduced.Considering the influence of shield excavation and grouting ring comprehensively,the calculation formula for the vertical displacement of the existing tunnel caused by the new tunnel excavation is deduced.(5)The influence of the grouting ring of the newly built tunnel on the control of the settlement of the existing tunnel was studied.Considering the volume expansion of the grouting soil,a mechanical calculation model for the volume expan sion of the grouting ring was proposed.Based on the random medium theory,the calculation formulas for the additional stress and vertical displacement of the existing tunnel axis caused by the expansion of the grouting ring are deduced.(6)This article optimizes and innovates the construction methods and indoor model tests related to control measures.Figure 118 table 10 reference 117... |
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