Deterioration Characteristics And Timely Variable Reliability Analysis Of Shield Tunnel Segments Under Sulfate Erosion

Sulfate erosion is an environmental erosion with a wide range of existence and great potential harm.In the sulfate erosion environment,the mechanical properties of the shield tunnel segment increase with the service time deteriorate due to the erosion effect of sulfate ions on the concrete,which will undoubtedly threaten the reliability of the tunnel structure during service.Therefore,the time-varying reliability of shield tunnel concrete segments under the sulphate erosion environment to quantitatively assess their safety has important theoretical and application value for ensuring the safe operation of tunnels and avoiding the occurrence of shield tunnel safety accidents.In this paper,taking a shield tunnel in the environment of sulfate erosion as the research object,starting from the deterioration law of the strength of the segment under the erosion of sulfate,the time-varying reliability of the segment of the shield tunnel is analyzed and studied according to the effect of strength deterioration.The main research contents and achievements of this paper are as follows:(1)On the basis of collecting and consulting a large number of documents,this paper combs the existing reliability research results,and determines the time-varying reliability calculation model and functional function form of shield tunnel segments under sulfate erosion,so as to provide a theoretical basis for reliability calculation.According to the form of function function,the first work to be completed in the calculation is to obtain the time-varying condition of segment bearing capacity and the sum of load effects borne by segments.(2)In order to obtain the time-varying function of the ultimate bearing capacity of the segment section during the service period,the sulfate attack indoor accelerated test was carried out on the concrete cut sample of the segment of a river crossing shield tunnel.The variation law of the compressive strength of the segment concrete under sulfate attack with time was studied.The function was fitted through the test data,combined with the relevant mechanical parameters of the segment concrete and reinforcement,The ultimate bearing capacity of segment section is calculated.The load structure model of tunnel segment internal force calculation is sorted out,and the classification and calculation method of segment load are determined;By comparing the analytical method with ANSYS finite element method,the total load effect of segments during the service of shield tunnel is calculated.(3)According to the failure mode of segment resistance and load effect under sulfate attack,the functional function is established.Considering different protective measures,different segment reinforcement grades and different segment reinforcement ratio,the timevarying reliability index of shield tunnel segments under sulfate attack is calculated by using the first-order second moment method.Finally,according to the research process and the calculation results of reliability index,the protection suggestions of shield tunnel segments against sulfate erosion are given.