Study On Shear-Seepage Coupling Characteristics And Mechanism Of Granite Fissure In Water-Sealed Cavern

The water-sealed cavern is an underground cavern buried at a certain depth below the stable groundwater level,seal oil and liquefied petroleum gas by using the water pressure of rock fissures,and mostly built in granite rock strata;rock blocks absorb water to the maximum moisture content due to long-term immersion in water,weakening the mechanical properties of rock blocks and fractures.Engineering practice shows that the main failure mode of surrounding rock is block instability,the key to solve this problem is to reveal the shear-seepage coupling characteristics and mechanism of granite fractures.based on the engineering conditions of water-sealed caverns,the shear-seepage coupling characteristics and mechanism of granite fractures under maximum free water absorption are studied,it is important to evaluate the stability of rock mass in such engineering.In this paper,the physical and mechanical properties of the maximum free water content granite are studied by carrying out the uniaxial and triaxial compression and fracture scanning electron microscopy tests of the maximum free water content granite,reveals the failure mechanism of granite under different confining pressures;the mechanical properties of granite fissure with different undulation heights under different normal stresses were studied through shear tests;carry out numerical simulation tests corresponding to laboratory tests to further reveal the shear characteristics of granite fissure;through the study of the basic mechanical properties of granite and granite fissure,and on the premise of verifying the feasibility of the numerical simulation test,the shear-seepage coupling test of granite fissure is studied.The main research results of the thesis are as follows:(1)The results of the triaxial test of granite show that the compressive strength and elastic modulus of the rock increase approximately linearly with the increase of confining pressure,combined with the macroscopic characteristics of the failure surface and the SEM scan results,it can be seen that as the confining pressure increases,the angle between the maximum principal stress and the failure surface decreases,and the vertical fracture surface is mainly tensile failure,and the inclined fracture surface is mainly shear failure.Under uniaxial compression,granite is mainly tensile failure,and under triaxial compression,granite is mainly shear failure;the test results show that the granite cohesion force c=26.84 MPa and the internal friction angle φ=51°.(2)The results of granite fissure shear test show that: shear failure modes are divided into two types,the specimens with straight and undulating heights of 2 mm were wear damage,and the specimens with undulating heights of 6 mm were wear damage and shear failure;with the increase of fissure roughness,the normal stiffness and shear stiffness increase;the basic friction angle and equivalent cohesion of rock fissure are obtained.(3)The basic physical and mechanical parameters of rock blocks and rock fissure are obtained by laboratory tests,numerical tests are carried out based on the continuous yield joint model,the numerical simulation results are in good agreement with the indoor test results,verify the rationality of parameter selection;the shear failure characteristics of granite fissure under high normal stress conditions are also studied.(4)Numerical tests of shear-seepage coupling in rock fissure based on continuous yield joint model,the test results show that the effect of seepage on rock is mainly to reduce the effective stress,the influence of rock on seepage is reflected in the phenomenon of dilatancy in the shear process,which increases the opening of rock fissure and unit discharge;with the increase of fissure roughness,the difference between initial friction angle and basic friction angle,the shear strength,normal shear expansion and unit discharge increase.