Robust Optimization Design Of Bolt-shotcrete Support Structure In Tunnel

The optimization design of tunnel support structure has always been an important research topic in the field of tunnel engineering.At present,the conventional optimization design methods,such as reliability design theory and corresponding probability limit state design method,have been applied and popularized in a certain range.However,such methods must be based on a well-defined statistical law of geotechnical parameters,regardless of the variability of the design factors,which put the conventional optimization solution at the edge of the feasible domain.When the noise factors fluctuate,the conventional optimization solution will deviate from the feasible domain and become infeasible.Robust optimization design fully considers the impact of noise factors on the optimization results in the beginning of the design,which can reduce the sensitivity of structural response to controllable or uncontrollable factors perturbation.When the controllable and uncontrollable factors deviate,the structure performance can still meet the design requirements.Based on this,this paper carries out a systematic and comprehensive study on the optimization design of the tunnel bolt-shotcrete support structure based on the robustness theory.Starting from the characteristics of bolt-shotcrete support structure technology,the action mechanism of bolt and shotcrete support structure was introduced.And the value of relevant parameters such as bolt length,distance and shotcrete thickness were explained.Then,the theoretical basis of the robust optimization design was introduced,and the standard deviation of the vertical displacement of the maximum vault was used as the robustness evaluation index for the tunnel's bolt-shotcrete support structure.Using FLAC^3D numerical simulation software calculate the tunnel vault displacement,and the numerical model was established based on the section K84+694 of Shiziling Tunnel as project background.The robust multi-objective optimization design of the support structure was carried out based on the simulation results,and the Pareto Front was established based on the non dominant solution.In view of the problem that the finding of the inflection point on the Pareto Front is easily affected by the design threshold,a new method of searching the inflection point was proposed.By studying the influence of design parameters on structural robustness,the trend of structural robustness with design parameters was analyzed,and the influence rule of different design parameters on structural robustness was obtained.The calculation method of the comprehensive cost of bolt and shotcrete support was studied and put forward.On this basis,taking support cost and structural robustness as constraint objectives,the MATLAB programming was used to calculate the corresponding non dominated solutions which formed Pareto Front,then a new inflection point search method was applied to find the unique optimal solution.To further promote the robust optimization design method,the concept of relative optimal solution was put forward to solve the problem of local optimal solution when the parameters was limited.Then the feasibility of the relative optimal solution was analyzed by an engineering example,which provided reference for the optimization design of the tunnel supporting structure.