Study On The Mechanical Deformation Characteristic Of Deep Foundation With Pile Anchor Structure Based On Strain Softening Model

The pile-anchor supporting system is widely used in deep foundation pit engineering with its unique advantages, the research on force and deformation of the supporting structure during excavation is a hot topic in foundation pit engineering. At present, At present, the mechanical and deformation of the pile anchor supporting structure of deep foundation pits most by using field monitoring in combination with numerical simulation, commonly used Mohr-Coulomb model to describe the strength characteristics of rock-soil mass for the numerical analysis of pile-anchor supporting in deep foundation pit, but used the strain softening model less which is more in line with the strength characteristics of rock-soil mass. Therefore, this paper relied on the foundation pit engineering of Changsha Public Security Bureau, High tech District Branch as engineering background, made field monitoring and analysed for the pile-anchor supporting structure in deep foundation pit; Used the finite difference software FLAC3 D to establish the numerical model of foundation pit, numerically simulated the force and deformation of supporting structure during excavation based on strain softening model, and then compared with the monitoring data, to analyse them combined with the Mohr-Coulomb model, studied the force and deformation law of pile-anchor supporting structure during excavation, the main research contents and conclusions are as follows:(1) Made field monitoring plan and completed the field monitoring work according to the foundation pit engineering examples, monitored the displacement on the top of pile、the deformation of pile body、surrounding ground settlement and the axial force of anchor cable, the results showed that: The horizontal displacement and vertical displacement of pile head overall showed a trend of increase as the foundation pit was excavating; The maximum displacement of the pile with the depth of excavation gradually decreased; When the excavation of foundation pit was completed, the maximum displacement of the pile body located on the lower position of pile body, and the displacement curve of pile body presented "arc" distribution; The surface settlement around the foundation pit overall increased gradually as the depth of excavation increased, and when the depth of excavation was deeper, the change rate of sedimentation was larger, needed focus on monitoring; The axial force of anchor cable at each layer will be gradually increased as the foundation pit was excavating, and the next anchor applied will make the axial force of last anchor cable increased slowly.(2) Adopted three dimensional numerical analytical method to simulate and analyse the horizontal displacement of pile top、the deformation of the pile body、the displacement of soil behind the pile and the axial force of anchor cable during excavation based on strain softening model, the results showed that: Application of prestressed anchor cable has a significant effect on deformation constraint of top of supporting pile; When the excavation depth was not deep, the deformation of top of pile is the largest; The maximum displacement of pile body gradually moved to the lower part of the pile with the depth of foundation pit increased; The overall trend of the soil in the shear sliding surface was sank and moved to the inside of foundation pit, but the overall trend of the soil outside the shear sliding surface swelled up and moved toward the foundation pit lateral; The anchor cable mainly tensiled in overall, the cable axial force of free segment basically unchanged and the axial force of anchorage section decreased gradually along the length direction, this mainly dued to the side friction of anchorage body affected the distribution of axial force of anchorage segment.(3) Through the comparison between two models and analysed combined with the test data, the results showed that: The results of numerical simulation were roughly consistent with the change rule of field monitoring data; To study the force and deformation of supporting structure in soft rock foundation pit, found the results of strain softening model was larger than the results of Mohr-Coulomb model, and was more closer to the results of actual monitoring, strain softening model was more in line with the actual situation, illustrated the correctness of the model and parameter selection, the validations for the numerical method and numerieal calculation results are proved, the result obtained by calculation can provide guidance for real projects.