A constitutive model considering friction property of geomaterials and stability analysis of borehole

The strength and deformation properties of geomaterials are essential to estimating the cracking behavior of rock, especially for deep exploration of conventional and unconventional hydrocarbon resources. Because the geomaterials encountered in hydrocarbon exploration are generally granular friction materials formed from deposition or cementation of granular materials in natural conditions, they sustain loads by means of intergranular friction, which forms the main source of their shear strength. Therefore, the deformation and failure of friction material is governed by the friction law. A mechanical element of the friction material is modelled based on the concept that the internal friction exists in both the elastic state and the plastic state. By assuming that the friction coefficient is proportional to the strain, the friction stress is computed, and then the corresponding nonlinear elasto-plastic constitutive model of the friction material is established. Based on analysis of the internal friction effect of rock during macroscopic shear deformation, the mechanical mechanism of geomaterials' friction strength enhancement is explained. The nonlinear elasto-plastic constitutive model was used to compute the fracture and failure of a tunnel and a deep borehole. The results show that the model is effective for estimating the mechanical response of important geotechnical problems, such as the analysis of cracked rock-mass strength, forecasting crack closure, and borehole wall collapse.