Study On Mechanical And Seepage Properties Of Sandstone Under The Coupling Of Temperature-seepage-stress

The mechanics and seepage characteristics of deep underground engineering rock mass under the coupling of temperature-seepage-stress are quite different from normal temperature,and the relevant research data are still slightly lacking.Based on this,this paper systematically studied the mechanical strength and seepage characteristics of sandstone under the condition of multi-physical field coupling by means of laboratory tests,theoretical research and numerical verification and analysis.The empirical parameters of M-C criterion and H-B criterion were revised by temperature,and derived the improved Duncan-Chang constitutive model with the consideration of temperature.Combined with the three-field coupling mathematical model,the improved constitutive model is embedded in the COMSOL Multiphsics software to verify and analyze the sandstone samples numerically.Relying on the improved model,the stress and deformation characteristics of the deep buried tunnel under normal temperature and high temperature are compared and analyzed.The main contents could be draw:(1)Uniaxial compression tests at different temperatures(25?,50?,75? and90?)and triaxial compression tests at different temperatures(25?,50?,75? and90?)and at different confining pressures(10MPa,20 MPa and 30MPa)were carried out on sandstone,and the change rule of mechanical and deformation indexes of sandstone were discussed.The temperature effect improves the deformability of the sample to a certain extent.In triaxial test,the mechanical effect brought by temperature increase is both weakened and strengthened,which is related to the primary mineral composition and fracture arrangement and distribution in the sample.The mean modulus increases with confining pressure and decreases with temperature.Temperature rise in a certain range increase the peak strain and improve the ductility of rock.The shear parameters of c and ? also decreases slowly when the temperature rises.The attenuation of c caused by temperature is more significant than that caused by the Angle ? of internal friction.(2)Triaxial compression seepage tests under different temperatures(25°C,50°C,75°C and 90°C),different water pressures(2MPa,5MPa and 8MPa),and the the change rule of mechanical and deformation indexes of the sandstone were analyzed.The peak strain increases slightly as confining pressure increases,and the high temperature improve the ductility of rock samples to some extent.The temperature rise in this temperature region has little effect on the modulus of elasticity.(3)The permeability of sandstone is related to macroscopic fracture development and secondary closure,the peak permeability lags behind the peak strength,and the permeability is closely related to confining pressure.An empirical model of permeability-temperature relationship under temperature-seepage-stress coupling was established by polynomial fitting of permeability-temperature curve based on test data.The minimum permeability of the sample does not correspond to the permeability at the maximum compactness,but appears before the inflection point of the volumetric strain-deviator stress curve,and the initial permeability,minimum permeability and maximum permeability under the action of temperature-percolation-stress coupling are analyzed.(4)SPSS was used to find out the main factors affecting the mechanical index and permeability performance.In addition to peak strain,the important factors are confining pressure,water pressure and temperature in order,while the degree of influence on peak strain is confining pressure,temperature and water pressure in descending order.The factors that affect the initial permeability are confining pressure,temperature and water pressure,the factors that affect the minimum permeability are confining pressure,water pressure and temperature,and the factors that affect the maximum permeability are confining pressure,temperature and water pressure.(5)The test data was used to analyze the characteristic parameters of the shear strength of sandstone under three field coupling effects.The M-C criterion considering the correction of temperature was obtained,and the H-B criterion parameters m,s under different temperatures were modified by using test data based on the Hoek-Brown criterion.Based on the results of the sandstone temperature-percolation-stress coupling test,the improved Duncan-Chang model with the consideration of temperature is derived,the significance of the physical characteristics represented by the dimensionless coefficient c,n is analyzed,and the improved constitutive model is verified by experiments.According to the principle of three-field complete coupling,the governing equations of each field are derived from the basic equations of each factor variable and the physical property equation,and the mathematical model of sandstone under the action of temperature-percolation-stress coupling is established.(6)The improved Duncan-Chang model,after considering the effect of temperature,was embedded into COMSOL Multiphysics software to conduct numerical verification and analysis of sandstone tests under the coupling effect of temperature-seepage-stress.Results show that the higher temperature results in the decrease of carrying capacity of the plastic deformation and temperature after the action of seepage rate increased,the abrupt change point of the seepage rate appeared earlier,but with increasing of confining pressure to lower fluid flow velocity in the rock,heterogeneous discontinuous deformation,seepage channel high confining pressure,the greater the seepage rate chart ups and downs,the greater the difference,leading to lower permeability.Import the revised M-C criterion and H-B criterion into the COMSOL to determine the plastic zone development of the specimen.Under the two criteria,the plastic strain of sandstone specimens increases with temperature,the development time of plastic strain brings forward,the range of plastic zone increases,and the plastic deformation intensifies.However,the plastic strain generated by the revised M-C strength criterion is greater than that of the H-B strength criterion.(7)Use of sandstone under the effect of temperature,seepage,stress coupling constitutive model of deep buried tunnel of high temperature high pressure and high in-situ stress are analyzed in numerical simulation,discusses the state of normal temperature and the total displacement of surrounding rock under high temperature,total stress and the plastic area,along the X axis and Y axis stress,osmotic pressure,heat transfer temperature field,the first principal stress and the third principal stress,the stress and deformation of supporting structure feature points distribution.And compare the difference between the improved Ducan-Chang model with temperature effect and the improved Ducan-Chang model without temperature effect constitutive model.The stress concentration and deformation are more severe in the deep tunnel under the temperature field.The stress and deformation calculated by the improved Ducan-Chang constitutive model embedded in the consideration of temperature are greater than those calculated by constitutive model without temperature effect,and the structural design calculated by the the improved Ducan-Chang model with temperature effect constitutive model is more secure.