| In deep complex geological environments,the power waves propagated in the surrounding rock by underground energy mining activities are within the range of low-frequency weak disturbances,which are frequent and of low energy level.Under high ground stress,the rock creep rate is accelerated,and the large deformations and instability may occur under low-frequency weak disturbances,and major safety accidents are caused.This brings a major risk to the stability and safety of the surrounding rock tunnel.Therefore,the creep characteristics of sandstone under low-frequency weak disturbance were studied by combined three research methods,namely laboratory experiment,theoretical analysis,and numerical simulation.The experiments on sandstone creep characteristics under low-frequency weak disturbance were carried out,using improved creep disturbance test equipment combined with a digital scattering system.Then the integer-order and fractional-order non-linear creep models were established to characterize the creep characteristics of sandstone under low-frequency weak disturbance.The identification analysis and sensitivity analysis were carried out on the parameters of the nonlinear creep models,also the integer-order and fractional-order nonlinear creep models were developed by using the FORTRAN language program.The main research contents and achievements of the thesis are as follows.(1)The sandstone creep experiment schemes under low-frequency weak disturbance were designed to carry out the creep characteristics tests under small low-frequency and micro small low-frequency disturbances.Therefore,the influence laws were revealed of disturbance frequency,disturbance amplitude,and disturbance mode on the creep deformation,creep rate,crack evolution,and failure characteristics of sandstone.Based on the fractal theory,the fractal characteristics of fracture evolution and damage state were quantitatively analyzed during the whole process of sandstone creep.The double tangent intersection method was proposed to determine the long-term strength of sandstone under the low-frequency weak disturbance.(2)The theories of rock rheology,fractional calculus,and damage mechanics were applied.For the nonlinear creep characteristics of sandstone under low-frequency weak disturbance,three factors of axial stress,disturbance amplitude,and disturbance frequency were considered,and damage factors were introduced to construct nonlinear elements.Then the integral and fractional order sandstone nonlinear creep models were established,and the two models were verified and analyzed according to the test results.(3)The parameters of the nonlinear creep models were identified and analyzed using the1st-opt software to reveal the influence of the key parameters of the creep model on the creep deformation.And the nonlinear relationships between disturbance factors and damage factors were explored.Therefore,the nonlinear creep deformation evolution characteristics of sandstone were unified and described by a constitutive model under low-frequency weak disturbance.(4)The influence law of a single change of model parameters on creep deformation was analyzed by the local sensitivity analysis.The correlations between the model parameters were explored by the global sensitivity analysis,and the mutual influence laws between the parameters of the creep model were obtained.(5)The numerical solution of the built integer-order and fractional-order nonlinear creep model was realized by using the UPFs development tool,and the verification analysis was carried out.The applicability and rationality of the two models for characterizing the creep deformation characteristics of sandstone were discussed under low-frequency weak disturbance.Moreover,the two nonlinear creep models were compared and analyzed from three perspectives.There are 98 figures,35 tables,and 234 references. |
