Analysis Of The Influence Of The Small Space Overlapping Tunnel Construction On Underpinning Pile Foundation Of Viaduct

In recent years,the level of science,technology and economy in China has been improved rapidly,which has further accelerated the process of urbanization.The rapid expansion of urban construction has made the surface space more crowded,and underground rail transit has become one of the irreplaceable means of transportation.In densely populated cities,high-rise building and the elevated bridge pile foundation is usually need to tens of meters deep into the ground hard formation,therefore,the subway tunnel line and the position of the pile foundation inevitably conflict,in the case of metro planning line cannot be changed,on the construction of main reinforcement of pile foundation with and for subway tunnel through the building of pile foundation.At present,China’s subway tunnel construction technology is still in the development stage,scientific research achievements are relatively limited,many engineering design parameters can only be estimated through experience,the construction process caused by excessive ground subsidence and the adjacent building damage is still widespread,therefore,in-depth research on this aspect is of great significance.First of all,this paper summarizes the experience and conclusions of previous scholars,and lists the deficiency of present research,and then briefly shield for pile foundation underpinning technology,construction principle and the influence law of the surrounding environment caused by tunnel excavation is described,and finally,typical engineeringexamples of overlap in shenzhen subway tunnel construction,through the establishment of three-dimensional numerical model,the overlapped tunnel excavation of underpinning pile foundation before and after simulated study the laws of internal force and deformation.The main research ideas are as follows:(1)According to the pile foundation underpinning scheme,the general situation of construction and geological conditions of overlapping tunnel,midas-gts finite element software is used to establish a three-dimensional model to simulate and analyze the process of pile foundation underpinning of the upper and lower overlapping tunnels passing through viaduct successively,and the laws of surface settlement and stress deformation of underpinning pile foundation are obtained,which are compared with the field monitoring data to confirm the results of numerical simulation Accuracy.(2)On the basis of the engineering case model,by changing the sequence of the top and bottom overlapping tunnel excavation,the length of the supporting pile foundation and the distance between the top and bottom two tunnels,a number of different sets of models were established respectively,and the variation law of the internal force and displacement of the supporting pile foundation was obtained,and the influence effect was analyzed.