Secant Modulus Method: A Simplified Technique for Measuring in Situ Stresses in Rocks

Abstract The core of sustainable mining is the preservation of the ground stability, and in situ stress measurement is crucial as most of the stability issues are directly associated with the in situ and induced stresses. Deformation rate analysis and acoustic emission are reliable and low-cost methods of stress measurement leveraging stress memory in rocks. However, owing to rock heterogeneity and complex geological stress history, the accurate determination of in situ stresses is often challenging. This study proposes a simple, accurate, and improved method for determining the in situ stresses in rocks called the Secant Modulus Method (SMM). The effectiveness of SMM is determined through uniaxial cyclic loading and unloading experiments on different types of soft and hard crystalline rocks. The influence of the loading modes, strain rates, and time delay is also investigated. Additionally, its utility for in situ stress measurement is explored. The SMM method proved effective in determining both applied and in-situ stresses, with no effect from variations in loading conditions, loading rates, and time delays. Moreover, the in situ stresses measured using the SMM were in good agreement with the overcoring method.