Study On Shear Creep Characteristics Of Rock And Structural Plane Under Multi-field Environment

With the construction of rock engineering in northern China,the long-term stability of rock engineering under the combined effects of low temperature,water,stress and chemistry（multi-field environment）has become increasingly prominent.In addition,the shear creep property is one of the important mechanical characteristics of rock engineering,which is closely related to the long-term stability of rock engineering.Therefore,the study of shear creep properties of rock mass under the action of multi-field environment is of great engineering value and academic significance.Considering that the rock mass is mainly composed of rocks and structural surfaces,this thesis selects typical granite rocks in the north of china,granite natural structural surfaces and cement mortar structural surfaces as the research objects.For the typical action of multi-field environment,shear creep tests under the action of dry and wet cycles,freeze-thaw cycles,freeze-thaw-chemical corrosion and pore water pressure were carried out respectively and corresponding creep damage model was also developed.Based on the 3DEC platform,a three-dimensional creep damage modeling program for rock and structural surfaces under the action of multi-field environments was developed,and validated and applied through tests and engineering calculations.The details of the study are as follows:（1）The granite microstructure observation and shear creep test under the action of multi-field environment（dry-wet cycle,freeze-thaw cycle and acidic freeze-thaw cycle）were carried out to analyze the influence law of multi-field environment on granite microscopic damage characteristics,creep deformation,creep rate and long-term shear strength,and reveal the shear damage deterioration mechanism of granite under the action of multi-field environment.The test results show that the creep deformation,creep rate and damage factor of the specimen increase gradually with the intensification of environmental effects,while the instantaneous shear modulus,failure stress and long-term shear strength all show a decreasing trend.Based on the Nishihara model,the coupled damage variables of environmental damage and load damage were given,and a granite shear creep damage model that can reflect multi-field environmental effects was established,and the validity of the model was verified based on experimental data.（2）The three-dimensional morphological parameters of granite structural surfaces were obtained by the self-developed three-dimensional morphological laser tester with features of fast scanning and high accuracy,and the experimental study of shear creep of granite structural surfaces with different three-dimensional roughness was carried out.On this basis,the three-dimensional morphological parameter measurement and shear creep test of granite structural surface under the effect of freeze-thaw-chemical corrosion were carried out,and the influence law of freeze-thaw-chemical corrosion on the three-dimensional morphological parameters of the structural surface was analyzed,and the influence law of freeze-thaw-chemical corrosion on the transient deformation,creep deformation,creep rate and long-term shear strength of the structural surface was investigated.The test results show that the instantaneous deformation,creep deformation and creep rate of the structural plane gradually increase with the increase of the number of freeze-thaw and chemical corrosion,while the instantaneous shear modulus and long-term shear strength gradually decrease,and the degree of influence on the structural plane creep parameters is H₂SO₄solution,Na OH solution and Na Cl solution in order from large to small.Based on Burgers model,freeze-thaw-chemical corrosion and load coupling damage variables were defined,and a shear creep damage model for structural surfaces considering freeze-thaw-chemical corrosion was established,and the reasonableness of the model was verified by experimental data.（3）The structural surface integrated fabrication mold and shear seepage sealing system were developed independently,the shear creep test of serrated structural surface under pore water pressure was carried out.With the increase of pore water pressure,the instantaneous displacement,creep displacement and steady creep rate of the structural plane gradually increase,and the tooth shaped structures sheared off after shear creep gradually increases,while the creep duration,failure stress and long-term shear strength all decrease.On this basis,a cement mortar structural surface was fabricated with a natural granite structural surface as a prototype,and shear creep-percolation tests on the structural surface under pore water pressure were carried out to analyze the evolution of shear displacement and permeability of the structural surface during transient,deceleration,steady-state and accelerated creep stages.Based on nonlinear creep theory and fractional order calculus theory,fractional order viscous elements are introduced,and the effects of pore water pressure and load damage on creep parameters are considered to establish a fractional order nonlinear shear creep model for the structural surface,and the rationality of the model is verified based on experimental data.（4）On the basis of the above study,the equations for the evolution of damage variables of rocks and structural surfaces under the action of multi-field environment are defined,and a three-dimensional creep damage model for rocks is established.And the tangential stiffness of the structural surface was transformed into a time function conforming to the Burgers creep damage model,and a three-dimensional creep damage model of the structural surface was established based on the continuous yielding C-Y nodal model.Then,secondary development based on the 3DEC platform was carried out to write the model program,and the rationality of the model was verified by experimental data.Finally,the developed model was applied to the long-term stability analysis of northern tunnels,and the influence laws of the number of freeze-thaw-chemical corrosion,structural surface distribution,creep time and pore water pressure on the creep characteristics of tunnels were analyzed.The calculated results are basically consistent with the existing literatures,indicating that the model can reasonably reflect the action of multi-field environment,and provides an effective calculation method for the long-term stability analysis of rock engineering in in cold regions.