To understand the strengths of rocks under complex stress states, a generalized nonlinear three-dimensional (3D) Hoek-Brown failure (NGHB) criterion was proposed in this study. This criterion shares the same parameters with the generalized HB (GHB) criterion and inherits the parameter advantages of GHB. Two new parameters, b, and n, were introduced into the NGHB criterion that primarily controls the deviatoric plane shape of the NGHB criterion under triaxial tension and compression, respectively. The NGHB criterion can consider the influence of intermediate principal stress (IPS), where the deviatoric plane shape satisfies the smoothness requirements, while the HB criterion not. This criterion can degenerate into the two modified 3D HB criteria, the Priest criterion under triaxial compression condition and the HB criterion under triaxial compression and tension condition. This criterion was verified using true triaxial test data for different parameters, six types of rocks, and two kinds of in situ rock masses. For comparison, three existing 3D HB criteria were selected for performance comparison research. The result showed that the NGHB criterion gave better prediction performance than other criteria. The prediction errors of the strength of six types of rocks and two kinds of in situ rock masses were in the range of 2.0724%-3.5091% and 1.0144%-3.2321%, respectively. The proposed criterion lays a preliminary theoretical foundation for prediction of engineering rock mass strength under complex in situ stress conditions. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.

Strength theory is the basic theory for calculating and designing the strength of engineering materials in civil, hydraulic, mechanical, aerospace, military, and other engineering disciplines. Therefore, the comprehensive study of the generalized nonlinear strength theory (GNST) of geomaterials has significance for the construction of engineering rock strength. This paper reviews the GNST of geomaterials to demonstrate the research status of nonlinear strength characteristics of geomaterials under complex stress paths. First, it systematically summarizes the research progress of GNST (classical and empirical criteria). Then, the latest research the authors conducted over the past five years on the GNST is introduced, and a generalized three-dimensional (3D) nonlinear Hoek-Brown (HB) criterion (NGHB criterion) is proposed for practical applications. This criterion can be degenerated into the existing three modified HB criteria and has a better prediction performance. The strength prediction errors for six rocks and two in-situ rock masses are 2.0724%-3.5091% and 1.0144%-3.2321%, respectively. Finally, the development and outlook of the GNST are expounded, and a new topic about the building strength index of rock mass and determining the strength of in-situ engineering rock mass is proposed. The summarization of the GNST provides theoretical traceability and optimization for constructing in-situ engineering rock mass strength.

Excavation-induced disturbances in deep tunnels will lead to deterioration of rock properties and formation of excavation damaged zone (EDZ). This excavation damage effect may affect the potential rockburst pit depth. Taking two diversion tunnels of Jinping II hydropower station for example, the relationship between rockburst pit depth and excavation damage effect is first surveyed. The results indicate that the rockburst pit depth in tunnels with severe damage to rock masses is relatively large. Subsequently, the excavation-induced damage effect is characterized by disturbance factor D based on the Hoek-Brown criterion and wave velocity method. It is found that the EDZ could be further divided into a high-damage zone (HDZ) with D 1/4 1 and weak-damage zone (WDZ), and D decays from one to zero linearly. For this, a quantitative evaluation method for potential rockburst pit depth is established by presenting a three-element rockburst criterion considering rock strength, geostress and disturbance factor. The evaluation results obtained by this method match well with actual observations. In addition, the weakening of rock mass strength promotes the formation and expansion of potential rockburst pits. The potential rockburst pit depth is positively correlated with HDZ and WDZ depths, and the HDZ depth has a significant contribution to the potential rockburst pit depth. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).