EXPERIMENTAL STUDY ON SHEAR STRAIN ENERGY AND MAXIMUM SHEAR STRAIN CHARACTERISTICS OF RED SANDSTONE

Direct shear tests of dry and saturated red sandstone samples under different normal stresses were carried out in rock shear test system to determine shear strength, shear strain energy and maximum shear strain characteristics. The influences of normal stress and saturated water on shear strength, shear strain energy density, and shear strain of red sandstone were analyzed in detail. Results show that the shear force-shear displacement curve includes evidently linear and yielding sections in dry and saturation states, respectively. The shear strength and the shear displacement increase significantly when the normal stress is 10 MPa~20 MPa. The shear displacement slightly changes when the normal stress is 20 MPa~40 MPa. Red sandstone demonstrates significantly lower cohesion and internal friction angle under compression and shear stress than under triaxial compression stress. Saturated water weakens the cohesion and internal friction angle under triaxial stress path but only weakens the internal friction angle under compression and shear stress path. When the normal stress is less than 20 MPa, shear strength degradation rate increases linearly with the increasing of normal stress. When the normal stress is 20 MPa~40 MPa, shear strength degradation rate fluctuates at certain value. A good linear relationship exists between peak shear strain energy density and normal stress, and the effect of saturated water on peak shear strain energy density increases with the increasing of normal stress. The peak shear strain energy density of dry and saturated red sandstone samples remains constant at 1.4579 and 1.0033 MJ/m³, respectively, and the degradation rate of peak shear strain energy density is 31.18%. According to the variation in the peak shear strain energy density with normal stress, empirical strength criteria of shear strain for dry and saturated red sandstone samples were established when 20 MPa normal stress was taken as turning stress. The conclusions demonstrated certain reference significance for engineering design and stability analysis of red sandstone engineering.