Multi-parameter Inversion Method Of Stress-seepage Coupling Creep Based On IA-BP Intelligent Algorithm And Its Engineering Application

Phyllite is a kind of soft rock with poor lithology,low strength and large deformation.It has obvious geological problems such as weakness,looseness and fragmentation.Soft rock can produce obvious plastic and creep characteristics under engineering force disturbance.Creep property of deep soft rock engineering is not only related to rock itself,but also to environment.For many soft rock projects,especially for tunnels or roadways buried deep underground,they are in complex environments,that is,multiple environmental fields are coupled and interact with each other,including stress field,seepage field,chemical field,temperature field and so on.The creep characteristics of rock under complex environment will have a great impact on the stability of the project,and it will be a potential safety hazard for the later operation of the project.In practical engineering,the stability of tunnel surrounding rock is usually analyzed according to the mechanical parameters of rock.However,rock is a heterogeneous,non-linear and discontinuous material.How to get the surrounding rock parameters simply,quickly and accurately has important guiding significance for practical engineering.Taking Shawan Tunnel of Weiyuan-Wudu Construction Project of "Lanzhou-Haikou National Expressway" as the actual engineering background,the similar material of phyllite was developed according to the similarity criterion,and the model test equipment was used to carry out the model test.Based on the field monitoring data and the displacement back analysis method,the stress-seepage coupling creep parameters of surrounding rock were inverted,and the inversion results were used.The parameters were analyzed by ABAQUS finite element method.The main contents include:(1)Based on Buegers constitutive model,the corresponding UMAT subroutine was compiled,and the correctness of Buegers subroutine was verified by uniaxial creep test using ABAQUS finite element software.(2)The back analysis methods of PSO-BP and IA-BP were established.The PSO-BP algorithm and IA-BP algorithm program were compiled by MATLAB software.The orthogonal table was established and used as learning sample.The PSO-BP algorithm and IA-BP algorithm were used to calculate the orthogonal table.The calculated and experimentalvalues of the two algorithms were compared.The comparison shows that IA-BP algorithm has better prediction effect.(3)Based on IA-BP algorithm,the mechanical parameters of surrounding rock were obtained by back analysis of field monitoring data.A three-dimensional finite element model was established by using ABAQUS finite element software,and the stability of surrounding rock of tunnel was analyzed by using step-by-step excavation method.(4)Based on the three similarity theorems,the similarity criterion of fluid-solid coupling is deduced,and the similarity criterion of creep stage is deduced.A kind of similar material of phyllite creep under seepage-stress coupling was developed.(5)Based on the actual engineering background of Shawan Tunnel in WWSY2 bidding section of "Lanzhou-Haikou National Expressway" construction project from Weiyuan to Wudu,the physical test model of Shawan Tunnel was made,and the model test was carried out using phyllite similar materials.