Stress-strain relationship in elastic stage of fractured rock mass

Discontinuity is the main factor affecting the stress-strain relationship of rock mass. Based on the statistical parameters of the fracture network of rock mass and combining them with the strain energy theory from continuum and fracture mechanics, the elastic stress-strain relationship of fractured rock mass is proposed and its elastic modulus is derived. The stress-strain relationship can truly reflect the weakening and anisotropy of the mechanical properties of rock mass. On this basis, experimental and calculated stress-strain curves are compared, both of which exhibited the same slope. Additionally, monitoring data from a tunnel excavation is compared with the numerical simulation results, indicating that the displacement of both is basically consistent. Then, we compare three constitutive models with the statistical mechanics of rock mass (SMRM) model to highlight the advantages of the latter in terms of reliability and adaptability. Finally, based on the results of a bearing plate test of a rock mass at Jindong Bridge, the anisotropy of the elastic modulus and its influencing factors are studied. The results show that the weakening and anisotropy of the elastic modulus of the rock mass are notable, and the modulus changes according to the inter-angle between the stress axis and the normal of the discontinuity, reaching the minimum at an angle of 57.5 degrees. The modulus is positively related to the friction angle and the cohesion of the plane and is inversely correlated to the average radius and density of the discontinuities. When the average radius of the discontinuities exceeds 3 m, the weakening of the elastic modulus of the rock mass tends to be stable. The stress environment also has an effect on the elastic modulus, which rapidly increases with the normal stress at the planes.