Study On Creep Characteristics And Critical Failure Constitutive Model Of Silty Mudstone

With the rapid development of infrastructure construction in China,more and more silty mudstone engineering problems are emerging.Especially the high and steep slopes,deeply buried tunnels,underground caverns and other engineering rocks formed by cutting silty mudstone rocks produces creep deformation in the long-term service process,destroying the rock structure and leading to the destabilization of the protection system,which brings great safety risks to the safe operation of the project.Therefore,the problem of creep deformation of silty mudstone has become a new issue that needs to be solved urgently,and the relevant departments have paid great attention to it.Thus,based on the National Natural Science Foundation of China(NSFC)projects(51838001 and 51908069),the present study investigates the creep characteristics and critical damage intrinsic model of silty mudstone using a combination of indoor tests,theoretical analysis and numerical simulations.The results obtained can help to solve the long-term deformation problems of silty mudstone related projects,and can provide theoretical and technical support for the design,construction and disaster prevention and control of silty mudstone projects,which has important theoretical significance and practical engineering value.The main research contents and conclusions are as follows:(1)Based on the relevant physical and mechanical properties of silty mudstone,the water-solid ratio plays an important role in the control of density,tensile strength and elastic modulus of siltstone similar material specimens formulated by orthogonal design tests.The barite powder ratio has a significant effect on the uniaxial compressive strength.The gypsum quality also has a significant effect on the density of similar materials of silty mudstone.(2)The best ratio of the silty mudstone similar material specimens is determined by the orthogonal design test ratio,combined with the results of the secondary refinement test;the pore size distribution and pore morphology of the silty mudstone similar material specimens and the silty mudstone raw rock specimens under the best ratio are analyzed and obtained by SEM test and MIP test,which verifies that the silty mudstone similar material specimens and the silty mudstone raw rock specimens are very close to the raw rock specimens.The pore size distribution and pore morphology of the silty mudstone similar material specimens are very close to those of the raw rock specimens.(3)The DZSZ-150 multi-field coupled rock triaxial pressure tester is used to test the triaxial mechanical properties of the specimens under different stress paths,and it is obtained that the peak stress and peak strain of the silty mudstone specimens increase with the increase of the surrounding pressure under the same loading rate;the elastic modulus also increases with the increase of the surrounding pressure;under the same surrounding pressure,the peak stress increases with the increase of the loading rate,and the peak strain decreases.Under the same circumferential pressure,with the increase of the loading rate,the peak stress increases and the peak strain decreases;the modulus of elasticity also increases with the increase of the loading rate,and the increase first decreases and then increases slightly.(4)Triaxial creep tests are carried out at different circumferential pressures,and the accumulated creep of the specimens showes approximately the same increasing trend with the increase of the loading level.Under the same circumferential pressure level,as the axial loading level increases,the creep rate of the specimen shows a larger initial creep rate,and with the passage of time,the creep rate decreases and gradually tends to a constant value.The creep rate in the accelerated creep stage is significantly higher than the deceleration creep and steady-state creep rate.(5)Based on the results of triaxial creep tests under different circumferential pressures,a new nonlinear viscoelastic-plastic creep intrinsic model(MKNVPB model)that can describe the full creep process of siltstone is established based on the basic theory of rock nonlinear rheology by connecting the generalized Kelvin body and nonlinear viscoplastic body in series,and based on the creep test data,the Levenberg-Marquardt(L-M)algorithm is used to identify the parameters of the model based on the creep test data.The rationality and feasibility of this intrinsic creep model are also verified,and the verification results showed that the new intrinsic model can well describe the creep deformation law of the whole process of creep damage of silty mudstone.(6)Based on the finite difference theory,the finite difference expression form of MKNVPB model for silty mudstone is derived,and the secondary development of nonlinear creep model is realized in Visual studio 2010 software by combining the built-in FLAC3D500VS2010Addin.msi plug-in of FLAC3D,and the dynamic link program of the model is obtained.And by comparing with the creep test curve and simulation curve,it shows that the two are close to each other,which verifies the correctness and rationality of the secondary development model program and provides a basis for the long-term stability study of this type of rock project.