Research On Safety Status Assessment And Risk Analysis Method Of Inner Support Structure

The internal support structure is widely used in deep foundation pit due for its strong support,strong adaptability and flexible layout,The research on the safety evaluation and risk analysis methods can timely discover the risks in the construction process and effectively reduce the probability of engineering accidents.Starting from the actual needs of the project,the article summarizes the typical deformation and internal force monitoring data of the internally supported support structure into safety evaluation indexes,puts forward the quantitative concept of evaluation indexes,establishes a risk analysis method of integrated deformation and internal force evaluation indexes by invoking the hierarchical analysis method,and systematically analyzes and verifies the feasibility of the method through model tests,numerical model simulations,and actual engineering exercises,and the main work and conclusions are as follows:（1）Summarizes the typical deformation and internal force monitoring indexes of the internally inner support structure,analyzes the problems in the process of internal force monitoring at the present stage,and proposes the method of back-calculating the bending moment by using the high-order spline interpolation function based on the inclination measurement data of the enclosure pile,which makes up for the deficiencies of the existing internal force monitoring means and verifies the effectiveness of the method through practical engineering calculations.（2）By quantifying the monitoring indicators into safety evaluation indicators with the help of monitoring alarm values in the specification,the inner connection of each safety evaluation indicator is established through hierarchical analysis model,and a risk analysis method with integrated deformation and internal force evaluation indicators is proposed after theoretical analysis,and the risk level range of the foundation pit is delineated according to the risk degree,which eliminates the need to subjectively determine the probability of risk occurrence and the degree of risk loss and effectively reduces the subjective factors in the risk evaluation process.（3）Designing and implementing independently model tests to analyze the basic law of force and deformation of the internally supported support structure;to address the problem of dividing the importance of each evaluation index in the risk analysis method,three different working conditions of soil excavation,slope top loading and support damage were set,and through the analysis of the characterization of deformation and internal force monitoring data under different working conditions,it was initially determined that the wall tilt,wall Bending moment should dominate the risk evaluation of internally supported support structure;in order to clarify the distribution of the weight coefficients of each evaluation index,the MATLAB numerical analysis software was used to conduct the relevant sensitivity analysis of each evaluation index,and the combination of the trial calculation results of different judgment matrices was used to determine the combination of weight coefficients with better evaluation effect.（4）In the analysis of the test results of the support damage stage,by comparing the changes of internal force and deformation of the foundation pit before and after the support failure,the influence mechanism of the support local failure on the support system is revealed,which provides reference for the reinforcement treatment when similar dangerous situations occur in the actual engineering,the research results show that: after the support failure,the load has obvious proximity transfer phenomenon,and the axial force of the support immediately adjacent to the demolition position increases obviously;the deformation has obvious proximity influence phenomenon,and the influence range of deformation spreads to the surrounding immediately adjacent supports with the demolition position as the center,but the immediately adjacent supports will limit the development of displacement.（5）Based on the discussion of different support types,different pit locations and different alarm value settings in actual projects,the principles of monitoring data processing and pit area partitioning are summarized and the specific process of risk analysis method is introduced;two cases with different engineering geological conditions and different risk actual conditions are selected to verify the applicability of risk analysis method and the judgment matrix with limited assignment interval is obtained.（6）Taking an actual project of an internally supported support structure in Binzhou as an example,the risk analysis was demonstrated for the whole construction process by combining the actual measurement data of deformation and internal force,and the final risk level of the foundation pit was determined,and the deficiencies in the construction process were analyzed according to the real-time changes of the risk degree with the working conditions,and a 3D simulation model was established with the help of PLAXIS 3D finite element software,and the calculated data of the model was combined with the article The calculation data of the model was combined with the risk evaluation method and experimental research results proposed in the article,and the changes of deformation and internal force of the components in the subsequent dismantling stage of the project and the feasibility of the dismantling plan were discussed.