Characterization Of Rate Sensitivity Triaxial Test Of Rock And Elastic-viscoplastic Constitutive Model Considering Strain Softening Behavior

With national transportation planning network extending to the Southwest and the Midwest from the east,inevitably,there will be a large number of tunnels constructed in some mountainous areas.The physical and mechanical properties of rock materials excavated in these tunnels are complex that damage and deformation caused by external load usually present time-dependent rheological properties.In previous studies,rock materials properties were mostly simulated numerically with ideal elastic plastic model which is not a good description of rocks' aging characteristics.Taking the Putaoling tunnel in the north section of the Hangzhou-Changxing Expressway as an example,this paper studies the elastic-viscoplastic constitutive model considering rock softening aging characteristics,based on the rate-sensitivity triaxial test of Putaoling sandstone.Hence,the paper consists of the following aspects:A basic physical test and a triaxial rate sensitivity test of gravelly sandstone in Putaling give a stress-strain curve of the sandstone under different confining pressures and different loading rates to conclude deformation characteristics and laws of rocks at different confining pressures and loading rates that the mechanics behavior of sandstone has significant rate sensitivity.It is the basis for obtaining the elastic and viscoplastic constitutive model parameters of sandstone in saturated state.Considering the aging deformation characteristics of gravelly sandstone,referring to the model of the lower load surface of the over-consolidated soil,according to the relative stress method,the paper takes the lower load surface of rock adjustment parameters as reference yield surface and introduces in two parameters related to material time.Furthermore,the paper applies current stress,viscoplastic strain and its rate as state variable dynamic yield criterion function,and gives iteration stress integration algorithm based on Newton-Raphson to successfully embedded into the large-scale finite element software ABAQUS for simulating rock triaxial sensitivity test.By using the three-dimensional tunnel model of the ZK125 + 65 ~ ZK125 + 110 section of the left line of the Putaoling tunnel established by the large-scale finite element software ABAQUS,the paper intends to build ideal elastic-plastic model and its numerical simulation of tunnel excavation,and verifies that compared to ideal elastic viscoplastic constitutive model,the newly established elastic-viscoplastic model is more sensitive to the increase of tunnel excavation speed,which can much more reflect the rate relevance of rock at duration of force bearing process force.The paper,with numerical simulation of elastic-viscoplastic model of the actual excavation at Putaoling,discusses changes of the displacement field,the stress field and the plastic strain zone of the surrounding rock,and effectively predicts mechanical behavior during tunnel excavation.The paper provides guidance for safe construction and verifies correctness of the constitutive model.