Study On Deformation Mechanism Of Adjacent Pile Induced By Shallow Tunnel Excavation

With the large-scale development and utilization of urban underground space,the urban tunnels have been extensively constructed.Thus,shallow buried subway tunnels crossing adjacent existing pile foundations are commonly encountered.In practical engineering,the tunnel and the most of the pile are constructed underground,which are not easyly to be observated.At present,soils employed in physical models are opaque materials.As a result,only the surface deformation of soil can be directly observated in the experiment,while the internal deformation of soil was measured in indirect and partial modes,resulting in the limitations of research on the pile foundation deformation mechanism induced by shallow buried tunnel excavation process.In the present study,a series of model tests based on transparent soil test technology were conducted to simulate the progressive excavation process of shallow buried tunnel affected by the adjacent existing pile foundation.The model test scheme was extended by3d numerical simulation.The pile foundation deformation mechanism caused by tunnelling process,internal deformation of soil body,the influence of pile length,relative position of tunnel and tunnel depth on adjacent existing pile foundation were investigated.The rationalitys of the experimental and numerical results were verified by comparison between the theoretical analytical solutions and numerical simulation results.The main conclusions are as follows:（1）On the basic of transparent soil test technology,the transparent soil mixed with n-dodecane,white oil and fused quartz sand with the same refractive index was prepared.In the physical model tests,the deformation fields of soil around the tunnel and pile foundation were obtained by 3-D fault measurement technology.（2）The three-dimensional deformation law of pile foundation and its dynamic development process caused by tunnel construction were studed.In addition,the influence of pile length,relative plane position between pile and tunnel and tunnel buried depth on the the adjacent existing pile foundation were discussed,indirectly reflects the deformation mechanism of pile foundation.Subsequently,the test results were compared with the round hole shrinkage theory and numerical simulation results.（3）According to finite difference program FLAC^3D,extend the model test,and the excavation process of shallow buried tunnel affected by the adjacent existing pile was numerically simulated.The ground settlement,lateral displacement,settlement,bending moment and axial force of pile for different pile lengths,pile-tunnel positions and tunnel burned were investigated.The mechanism of adjacent pile foundation deformation induced by shallow tunnel excavation was summarized.