An Improved Strain-Softening Damage Model of Rocks Considering Compaction Nonlinearity and Residual Stress Under Uniaxial Condition

To reflect the influence of saturation effect, an improved strain-softening damage model is established to link the saturated rocks with the dry rocks. First, the original damage model is improved to describe the characteristics of each stage in the uniaxial compression. According to the change of the tangent modulus from the compression phase to the elastic stage, an improved strain-softening constitutive model reflecting the nonlinear change characteristics of the compression phase is established. According to the change of the energy during the uniaxial compression, the energy consumption coefficient (λ) is introduced to replace the damage ratio coefficient to describe the deformation characteristics of the rocks when the residual stress or failure is reached. The specific physical meaning and calculation method of the energy consumption coefficient are given to correct the shortcomings of the damage evolution in the original model. Then, the relationship between the parameters in the new model for the dry rocks and the saturated rocks is analyzed. Based on the constitutive model of the dry rocks, a new constitutive model which can reflect the influence of the water-weakening is established. Finally, the stress–strain curves of different rocks are fitted by the established model, and good results are obtained. The physical meaning of each parameter in the model is clear, and each parameter can be obtained by the test results. The improved constitutive model can be applicable to both the dry rocks and the saturated rocks.