Research On Internal Force Inversion And Deformation Prediction Of Braced Envelope Structures

Internal support is a common form of excavation supporting structure,composed of inner support and supporting piles or inner support and diaphragm walls.It can effectively control the deformation on both sides of the retaining structure,and is widely used in practical engineering.More horizontal displacement monitoring and less internal force monitoring of enclosure structure in practical engineering,However,the internal forces of the enclosure structure are particularly important in the design.Based on the measured data of engineering,this thesis establishes the functional relationship between the displacement,the bending moment and earth pressure.Back analysis of bending moment and earth pressure based on displacement,through the measured data in practical engineering,the feasibility of the inverse analysis method is verified by comparing the inverse analysis data with the measured data.At the same time,the indoor model tests of the inner support are further carried out to simulate the excavation and loading process.The accuracy of the inverse analysis method is verified by the model test and numerical simulation data.In addition,the deformation and stress law of the internal support retaining structure under different working conditions are analyzed through the test data.Combined with two excavation engineering cases of inner support with supporting piles and diaphragm walls with inner support,internal force inversion and deformation prediction of retaining structure based on measured displacement data,hoping to provide some reference for the support design of excavation engineering.The main work and conclusions are as follows:(1)Based on the cubic spline theory,the quintic spline theory is deduced,the displacement back analysis of bending moment and earth pressure by the quintic spline theory,and the back analysis is carried out by combining two internal support excavation engineerings,the data obtained by inverse analysis are consistent with the measured data,which verifies the feasibility of the quintic spline theory.(2)The indoor model test analyses the internal support enclosure structure's deformation and internal force variation law.With the excavation and loading of the foundation pit,the deformation of the internal support retaining structure is a “bow”,and the maximum deformation occurs above the excavation surface.At the internal support position,due to the negative bending moment caused by the axial force of the support,the overall bending moment increases with the working condition,and the earth pressure in the active area behind the retaining structure decreases with the excavation of the foundation pit.At the same time,the back analysis theory is verified according to the indoor model test data and simulation data,and the rationality of the quintic spline is further verified.Finally,the BP neural network is used to invert the soil parameters of a certain working condition,and the inversion parameters are used to effectively predict the displacement of the next working condition.(3)According to two engineering cases of supporting piles with inner support and diaphragm walls with inner support,the deformation characteristics and axial force changes of the enclosure structure at different positions of the internal support system under different working conditions are analyzed.and the internal force of displacement under different working conditions is inversely analyzed by the quintic spline method.and the application of quintic spline theory in practical engineering is introduced.Finally,according to the displacement under a certain working condition,the BP neural network is used to conduct the back analysis of the soil parameters under this working condition.The displacement and bending moment under a certain working condition are calculated using the back analysis parameters,and the bending moment obtained by the back analysis of the measured displacement and the quintic spline displacement are compared.When the two are close,the accuracy of the back analysis of the soil parameters is reflected.The back analysis parameters can be used to predict the displacement of the next working condition,and provide some reference for the safety judgment of the foundation pit in practical engineering.