Study on the Generalized Zhang-Zhu Strength Criterion Considering Different Loading Paths of True Triaxial Tests

Abstract

ABSTRACT Rocks in true triaxial stress states (σ1> σ2> σ3) have received much attention with the construction of deep underground engineering. True triaxial tests accurately reflect the triaxial stress state of rocks and have been widely used in the developments and validations of the three-dimensional strength criteria. Different loading paths are arranged to assess the deformation and failure properties of rocks as the development of true triaxial tests. In this study, the loading paths of the true triaxial tests are summarized as the traditional loading path, Lode angle loading path, and mean stress loading path. The ratios of σ2 and σ3, Lode angle, and mean stress can be regarded as invariants for three loading paths, respectively. The alternative expressions of the generalized Zhang-Zhu strength criterion of different loading paths are obtained by combining the three invariants. The expressions incorporate the properties of three loading paths to represent the correlations between σ1 and σ3 in simple forms. Finally, the typical rock data of three loading paths are collected to investigate the characteristics of the triaxial test data and the alternative expressions. The results show that the alternative expressions accurately predict the rock strength for different loading paths and reflect the effect of invariants of the loading path on rock strength. Adoption of three loading paths is discussed, and it is noted that the appropriate loading paths should be selected according to laboratory conditions and research priorities. INTRODUCTION With the extensive utilization of underground space, mineral, and environmental resources, the construction of deep underground engineering has been rapidly developed (Xie et al., 2017). Deep underground engineering is confronted with a complex environment such as high ground stress, high ground temperature, and strong disturbance (He et al., 2005; Qian and Zhou, 2018; Zhu et al., 2019). The mechanical behavior of deep rock is significantly different from that of shallow rock. Numerous studies indicated that the stress of deep rock presents a three-dimensional (3D) unequal characteristic (σ1>σ2>σ3) (Haimson and Rudnicki, 2010; Zhu et al., 2013; Zhu et al., 2017; Cai et al., 2021), which is defined as true triaxial stress state. Therefore, the strength characteristics of the rock cannot be effectively reflected by conventional triaxial tests (σ1>σ2=σ3) because the effect of σ2 is neglected (Zhang et al., 2013; Ma et al., 2017; Lu et al., 2020). It is important to study the mechanical properties of rock under true triaxial stress states.