Research On The Unloading Rheological Mechanical Properties Of Sandy Mudstone

Soft rock has more complex mechanical properties than hard rock, they often show engineering mechanics properties such as change of strain softening, rheological property and nonlinear large deformation when as the engineering rock mass, and are key factors which influence the stability of engineering for a long time, it is of great significance to work hard on the mechanical properties research of soft rock. This article selects sandy mudstone of soft rock tunnel as research object, research on its mechanical properties through the indoor test, the main research contents are as follows:1) Use RMT-150c rock mechanics test system do sandy mudstone triaxial compression and unloading tests, study the strength, deformation and failure characteristics of the rock under different stress paths, and get the basic mechanical parameters under compression and unloading stress path.2) In triaxial compression and unloading tests, the peak intensity of sandy mudstone samples could not be determined according to the stress-strain curve directly, in order to solve this problem, a semilog method is introduced to the analysis of test data, the peak strength value of the samples are determined conveniently through1g(σ1-σ3)～ε1and σ3～1gε1relationship curve, and the reasonability of the accessor method is verified based on the relationship curve|△/△(σ1-σ3)～(σ1-σ3), which is the relationship between the stress increment, strain increment and stress.3) Use RLW-2000microcomputer control rock triaxial creep testing machine do rheological test under the two stress path of step unloading confining pressure with axial stress constantly and unloading confining pressure with axial compression on sandy mudstone, comparative analysis of the changing rule of the axial and lateral deformation with time of sandy mudstone samples under the two stress path. The rheological deformation characteristics and the law of development of rate of sandy mudstone under accelerated creep stage are discussed. Determine the long-term strength of the sandy mudstone sample under different initial unloading confining pressure through isochronous curve method, and introduce the concept of strength ratio to comparative analysis the proportion relationship between long-term strength and failure stress under the two stress path. Analyse the failure characteristics and its law of development with the change of initial unloading confining pressure of sandy mudstone samples under different conditions. 4) Based on unloading rheological test curve, adopt the visco model describe therheological characteristics of sandy mudstone under the condition of stress level less than s, and use Levenberg-Marquardt optimization algorithm identify rheological parametersin the model optimally.5) Select the visco model as the foundation, build a new nonlinear visco-elastoplasticrheological model through bring in nonlinear visco-plastic rheological component, so it canbetter describe the nonlinear accelerating rheological section of sandy mudstone’s wholeprocess of rheological curve under damage confining pressure, the verification resultsshow that the stress-strain curve calculated by this model tallieswell with the test curve,which show that the established nonlinear visco-elastoplastic rheological model isreasonable.6) Carry out numerical implementation on the new nonlinear visco-elastoplasticrheological constitutive model in FLAC3D, and apply it to calculate and analyse thelong-term stability of a hydropower station diversion tunnel, the research results canprovide certain reference value for the research of long-term stability of the tunnelsurrounding rock and the analysis of the tunnel’s long-term running safety.