| The pressures of ground traffic can be greatly alleviated and the travel quality of urban residents can be improved by the efficient use of urban underground space to develop subway construction.With the intensive development of the metro rail transit network,it is inevitable that the construction of urban subway tunnels will pass through the busy urban areas with dense buildings and complex hydrogeological conditions.In the construction of urban subway tunnels,shield has become the main construction due to its advantages of mechanization,high degree of automation,fast construction speed,and small impact on the ground environment.It is common that the engineering accidents such as ground collapse,inclination and even collapse of adjacent buildings will be caused by tunnel construction.Due to the complex interactions between tunnel,soil and pile,the displacement control standard of adjacent inservice piles during tunnel construction is lack of rationale.It is urgent to carry out relevant research on the displacement of adjacent soil and the deformation mechanism of in-service piles during the construction of subway tunnel,and solve the key theoretical problems of disaster prevention and control of adjacent in-service pile.In view of the above problems,the studies have been carried out by means of indoor test,model test,numerical simulation and theoretical analysis,a calculation method of ground and deep soil displacement caused by tunnel excavation considering the influence of existing piles was proposed,an analysis method of deformation mechanism of adjacent piles during tunnel construction was established,and a refined simulation of the response of adjacent piles caused by tunnel excavation was formed.Some useful conclusions have been obtained.(1)A multi-parameter shield testing machine is developed to realize the precise simulation of shield tunneling.A model test on the settlement of adjacent soil and the response of adjacent piles caused by tunnel excavation with different pile lengths,different pile diameters,different pile-tunnel distances and different pile head loads has been carried out.The influences of pile lengths,pile diameters,pile-tunnel distances and pile head loads on the settlement of soil caused by tunnel excavation were revealed,and the change patterns of axial force of adjacent piles with different pile length,different pile diameter,different piletunnel distance and different pile head load caused by tunnel excavation were expounded.Considering the change and development process of surrounding soil displacement during shield tunnel excavation,the calculation processes of soil displacement caused by tunnel excavation were divided into three parts.Based on Mindlin’s solution,a modified calculation method of surface and deep soil displacement caused by tunnel excavation considering the influence of existing piles was proposed.(2)A large visual constant stiffness cyclic shear apparatus was independently developed.Based on the diameter curve of the super-long bored pile test,a simulation method for the surface roughness of the concrete piles was constructed,and concrete shear test blocks with different roughness were formed.The monotonic shear and cyclic shear tests of concrete-soil under different roughness were carried out,and the shear characteristics of the pile-soil interface under different normal pressures were studied.The relationship between the shear strength of the pile-soil interface and the surface roughness of the concrete piles was analyzed,and the loading and unloading behavior of the pile-soil interface was obtained.Based on the modified calculation method of soil displacement caused by tunnel excavation considering the reinforcement effect of pile,considering the nonlinear load-unloading behavior of pile-soil interface and the coupling effect of vertical and horizontal deformation of pile caused by tunnel excavation,a two-stage analysis method of nonlinear deformation characteristics of single pile was established.Considering the interaction and the reinforcement effect between individual piles,a two-stage analysis method of bearing characteristics of pile groups considering the coupling effect of vertical and horizontal deformation of pile groups was proposed.(3)The nonlinear loading-unloading transfer models of pile-soil system were introduced into the contact interface calculation of ABAQUS software,and the secondary development of ABAQUS software was developed by using the subroutine FRIC.Considering the construction parameters,e.g.cutterhead thrust,shield friction,and grouting pressure,and environmental factors,e.g.different pile length,pile diameter,pile bearing state and piletunnel relative position,a refined simulation method for the response of surrounding piles caused by tunnel excavation was proposed.The influences of tunnel excavation on surrounding soil displacement were analyzed,and the response of adjacent piles caused by tunnel excavation was obtained,which can be used to guide the shield construction practice of the tunnels. |
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