Loading or unloading process in axial direction and Young’s modulus of rock specimen

The stress path of failure of rock mass is very complicated,which is different to the loading path of specimen in laboratory.In this paper,experiments of loading and unloading in axial direction of specimens were carried out in servo_controlled testing machine to study the deformation property of rock.There are fissures and cracks in specimen,which will close,slip and produce friction gradually in loading process.The maximum value of friction between fissures in specimen is influenced greatly by the axial stress and confining pressure,but the actual value is related to the local stress condition.In unloading process the direction of friction will convert to prevent restoration of shear deformation between the fissures,which results in the residual deformation in the specimen.The effect of confining pressure on Young’s modulus is related to the damage state of rock,but can not be shown by Young’s modulus directly.