| Pipeline corridor construction is developing rapidly,but there are still some problems in excavation and filling of pipeline corridor in mountain cities.CFG pile-soil composite foundation treatment technology is widely used because of its outstanding bearing performance and low engineering cost.In this thesis,numerical simulation and physical tests are used to study the bearing properties of the composite foundation of pipe gallery foundation pit in mountainous cities.The main work and achievements of this thesis are as follows:(1)The bearing characteristics of the retaining pile in the process of foundation pit excavation are studied,and the bearing deformation and surface settlement characteristics of the retaining pile under the condition of natural foundation and CFG pile-soil composite foundation are identified.The difference of the influence of two construction methods of CFG pile on the stress and deformation of envelope pile is compared and analyzed.The influence law of the diameter,spacing and embedment depth of the pile on the horizontal deformation,internal force and surface settlement outside the pit is studied.Combined with the material characteristics of the pile,the flexural capacity of the pile is evaluated.(2)Based on the construction procedure of CFG pile before foundation pit excavation,a series of numerical models are established to study the bearing characteristics of foundation pit retaining pile under the condition of CFG pile-soil composite foundation reinforcement.The influences of CFG pile length,pile spacing and layout form on bearing characteristics of foundation pit retaining pile and surface settlement and deformation are mainly analyzed.The influence sensitivity of various factors on bearing properties of retaining pile was found out.(3)Research is carried out on the bearing characteristics of CFG pile-soil composite foundation under the unloading condition of foundation pit excavation,studies the distribution law of rebound deformation of composite foundation,internal force and deformation of CFG pile under different excavation stages,and identifies the spatial distribution difference of stress and deformation of CFG pile.The influence of CFG pile length,pile spacing and layout on bearing properties of composite foundation is studied,and the sensitivity of each factor to bearing properties of composite foundation is identified.(4)Using physical model test,the vertical bearing characteristics of CFG pile-soil composite foundation under horizontal stratum condition are studied,and the settlement of composite foundation and the internal force distribution law of CFG pile are identified.Based on the numerical simulation method,the calculation model from the excavation of pipeline corridor foundation pit to the construction of pipeline corridor structure is established.The vertical bearing characteristics of CFG pile-soil composite foundation of underground pipeline corridor are studied,and the bearing characteristics of the two composite foundations are compared and analyzed.Combined with the above calculation results,the differences of bearing properties of CFG pile-soil composite foundation under excavation unloading and vertical loading are compared and analyzed.Finally,considering the length of CFG pile,pile spacing and layout,the vertical bearing properties of CFG pile-soil composite foundation in underground pipeline corridor are studied,and the sensitivity of different influencing factors to the settlement of composite foundation and the internal force of CFG pile are identified,and the bearing capacity of the foundation under different working conditions is calculated. |
