Visco-elastoplastic solution for surrounding rock cavern by considering brittle drop of post-peak strength

The full stress-strain curve of rock is often simplified into a three-stage model.The stress-strain relationship in the softening stage of the model is linear, while the process of strength decline after peak is neglected.The theoretical solution of surrounding rock of cavern obtained has some errors compared with the actual measurement.Therefore, aiming at the traditional three-stage model neglecting the characteristics of the actual path after the rock peak, the completed stress-strain curve of rock is simplified to a four-stage model to reflect the brittle drop characteristic of post-peak strength.The dilatancy and rheological properties of surrounding rock are considered, the stress and displacement equations of each zone in the four-stage model are derived, and the formula about post-peak strength drop is introduced to obtain the solutions of each partition radius.By comparing the zoning radius calculated by the method proposed with other methods, the applicable range of formula about post-peak strength drop is obtained.The displacement of tunnel wall calculated by the method is compared with the measured results, which verifies the feasibility of the method.In addition, the effects of softening modulus, rheological properties and other factors on stress, displacement and each partition radius of surrounding rock are analyzed.The results show that the radius of surrounding rock zoning is affected to a certain extent, while the rheological properties of rock and the stage of strength drop after peak are considered and the radius of zoning increases with the increase of strength drop coefficient after peak.When the range of rock strength drop coefficient is between 0.6 and 1, the calculated displacement of the tunnel wall is close to the measured value.The softening modulus has a greater influence on the wall displacement and zonal radius.The influence on the visco-plastic softening zone of surrounding rock is greater than that on the visco-plastic strength drop zone.Furthermore, the influence of rheological properties on the surrounding rock is mainly reflected in the displacement and circumferential stress of the wall.The research results provide a reference for the prediction of key data such as visco-plastic range and displacement of deep cavern.