Study on the difference of deformation and strength characteristics of three kinds of sandstone

In order to clarify the differences and the intrinsic causes of mechanical behavior of three kinds of sand- stone,the conventional triaxial test for three kinds of sandstone were carried out by RMT-150B rock mechanics test system,and the deformation,strength and failure characteristics of three kinds of sandstone were analyzed. The results showed that the yield characteristics of white sandstone and red sandstone were obvious,and the plastic deformation were remarkable,with the increase of confining pressure,the yield stage increased gradually,while the yield character- istic of yellow sandstone was not obvious and less affected by confining pressure. The higher the uniaxial compressive strength of sandstone is,the more significant the effect of confining pressure on its strength is,and the effect of confining pressure on the compressive strength of yellow sandstone was remarkable. The improvement degree of elastic mod- ulus and deformation modulus of sandstone influenced by confining pressure is proportional to the magnitude of elastic modulus and deformation modulus under lower confining pressure,and the influence of confining pressure on elastic modulus and deformation modulus of yellow sandstone was significant. The difference of internal friction angle between the three kinds of sandstone was large,while the difference of cohesion was small. Therefore,the strength difference of the three kinds of sandstone is mainly caused by the difference of internal friction angle. Brazilian splitting strength of sandstone is 3. 5% -5. 8% of uniaxial compressive strength. The confining pressure influence coefficient of the three kinds of sandstone decreased in a negative exponential relationship with the increase of confining pressure,and 20 MPa is the turning point of speed change of the confining pressure influence coefficient. Three kinds of strength criteria were analyzed through the experimental data,it is pointed out that the strength function of Mohr strength criterion can better reflect the non-linear characteristics of rock strength under different confining pressures. The typical slow dip angle shear failure occurs in white sandstone,and its fracture plane is plane. the tension-shear composite failure of red sand- stone and yellow sandstone occurs under lower confining pressure,and steep dip angle shear failure occurs under high- er confining pressure,the fracture plane of red sandstone is conical,while that of yellow sandstone is uneven.