Study On Deformation And Stability Of Pile-anchor Support Structure In Deep Foundation Pit

After decades of development,the design concept of foundation pit engineering has gradually changed from strength control to deformation control,and the pile-anchor support structure has become increasingly widespread in the northwest region because of its advantages of limited displacement,simple process,and relatively low cost.However,due to the regional complexity of the pit engineering and the surrounding environmental uncertainty,all the deep foundation pit projects cannot be generalized.This involves the theoretical development of different support structures for different foundation pit projects.The existing foundation pit engineering theory is based on semi-empirical and semi-theoretical results that have been developed based on practice and development,and there are still many deficiencies.Therefore,it is necessary to study the deformation law of deep foundation pit supported by pile-anchor in this area,the influence law of different soil constitutive models on stability and the sensitivity of different design parameters to the stability safety factor.The specific work is as follows:(1)After analyzing the deformation mechanism and calculation method of the foundation pit supporting structure,consider that the earth pressure will change with the excavation depth due to the soil unloading effect during the excavation of the foundation pit,so the soil behind the pile the body adopts the earth pressure model considering the influence of unloading.The soil below the excavation surface is assumed to be soil spring.The deflection differential equation of the supporting pile is established and the displacement of the pile body is solved by the difference method.Finally,based on the engineering examples and finite element numerical simulation methods,the results show that the pile displacement calculated by this method is reasonable and reliable.(2)Study on the stability of foundation pit excavation through finite element numerical simulation.Calculate the overall stability safety factor of the pile-anchor retaining structure by introducing two different soil constitutive model MC model and HS model through strength reduction method.As a result,it was found that the corresponding safety factor of the HS model is slightly higher than that of the MS model.This is because the HS model can simulate the real loading and unloading process and the result is more realistic.Finally,it compares with the three slicing methods and finds the strength reduction method.The calculation result is larger than the calculation result of the segment method.Because the segmentation method assumes too many conditions and the soil interaction cannot be considered,the strength reduction method is more suitable for evaluating the stability of the deep foundation pit supported by piles and anchors than the slicing method.(3)By establishing a safety factor sensitivity analysis model based on design parameters,the change law of the influence of the two parameters of the natural parameters and the artificial design parameters on the stability factor is analyzed,and the design parameters are defined as the main design variables according to the influence degree of each design parameter.Minor design variables and design invariants,and finally through the analysis and summary of the recommended values for partial design parameters of the pile-anchor retaining structure in the region,which can be used as reference and guidance basis for the design of pile anchored support structures in the region.