Applying Reactivation Tendency Analysis and Mohr-space to Evaluate Shear Strength Decrease and Anisotropy with Pre-existing Weakness(es) under Uniform Stress State

Abstract

Understanding the mechanical controls on shear strength decrease due to preexisting weakness is a fundamental problem in tectonic studies. In this study, by applying reactivation tendency analysis theory, a theoretical framework and defined Shear-strength Coefficient (f d) are developed for evaluating the shear-strength decrease and anisotropies due to the presence of preexisting weakness(es). The proposed study managed to overcome the restrictions of previous studies assumption that a pre-existing weakness plane contains the intermediate stress (σ 2) and vertical or horizontal orientations of principal stresses (Andersonian stress state). A new graphical technique (Mohr-space) was utilized to predict the shear-strength decrease and anisotropies caused by preexisting weakness(es). The Mohr-space technique made easier to visualize the state of stress and results of shear strength changes and able to build the quantitative and intuitive relationship between Shear-strength Coefficient (f d) and weakness relative-orientation(θ',φ›), weakness mechanical properties (C w and μ w) and relative σ 2 (3 2 2 1 σ σ σ σ − −)in any uniform tri-axial stress state.. In this study, Shear-strength decrease and anisotropies of a rock sample are evaluated theoretically, and shear strength properties and deformation characteristics of a geological body with multiple pre-existing weaknesses are analyzed and predicted.