| Increase in the number of urban subway and scale expands unceasingly,lines intersecting in both the tunnel construction under the new tunnel caused by more and more cases.Nanning,metro line 2 east extension project of main entrance line oblique crossing engineering,tunnel clear distance between only 2.3m,the tunnel of about23.2 °,this project as the background,from the theory study,numerical simulation and the measured data from several aspects such as the construction of shield tunnel under the oblique wearing both the study of the influence law of tunnel construction.(1)Based on the Pasternak two-parameter foundation model,the two-stage analysis method is adopted to obtain the numerical solution of the vertical deformation of existing tunnels caused by down-crossing construction,and some factors affecting the deformation of existing tunnels are analyzed with the help of Matlab software.The results show that the deformation value of the existing tunnel increases with the increase of the foundation bed coefficient,while the change of poisson’s ratio has little influence on the tunnel deformation.Therefore,the determination of the foundation bed coefficient should be obtained through relatively accurate field tests to ensure the accuracy of the results in the study of such problems.The Angle between the axes of the two tunnels has a great influence on the deformation of the existing tunnels,and the influence range of the included Angle becomes smaller,so it is necessary to avoid the construction of the under-passing with a small Angle.In addition,with the increase of formation loss rate,the existing tunnel deformation value will also increase correspondingly.(2)Midas/GTS finite element software was used to build a three-dimensional model to simulate the construction process of a new shield tunnel with oblique underpass through the existing tunnel,and to study the formation deformation and surface subsidence caused by oblique underpass construction and the influence rules on the existing tunnel.The results show that the main influence range of shield tunnel construction is within 4D(D is the tunnel excavation diameter)distance of the crossing position,and within 1D distance of the existing tunnel,the subsidence and deformation rate of the surface and the stratum is the fastest and the largest.Therefore,appropriate reinforcement measures should be taken for shield tunnel construction in this area.In addition,influenced by the skew between the two tunnels,the tunnel deformation at thefirst crossing side is obviously larger than that at the second crossing side,and the maximum settlement area of the tunnel gradually shifts from the east side to the west side with the advance of the cutter plate.At the same time,the existence of the existing tunnel plays a role of "blocking" the formation deformation,which is of positive significance for deformation control.(3)The measured results show that surface subsidence and tube segment deformation mainly occur in the range of 24 m before and after the cross position of the cutter disc,which conforms to the range of 4D.In addition,with the knife dish to move forward,the surface settlement,settlement of segment presents three obvious stage of development,namely "ahead of subsidence stage,shield shell support phase,deformation of shield tail out again accelerate stage",also confirmed that both the tunnel of stratum deformation restrain indeed,in line with the changing rule of the numerical simulation. |
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