A novel indirect optical method for rock stress measurement using micro-deformation field analysis

Abstract

Stress measurement plays a crucial role in geomechanics and rock engineering, especially for the design and construction of large-scale rock projects. This paper presents a novel method, based on the traditional stress relief approach, for indirectly measuring rock stress using optical techniques. The proposed method allows for the acquisition of full-field strain evolution on the borehole's inner wall before and after disturbance, facilitating the determination of three-dimensional (3D) stress information at multiple points within a single borehole. The study focuses on presenting the method's theoretical framework, laboratory validation results, and equipment design conception. The theoretical framework comprises three key components: the optical imaging method of the borehole wall, the digital image correlation (DIC) method, and the stress calculation procedure. Laboratory validation tests investigate strain field distribution on the borehole wall under varying stress conditions, with stress results derived from DIC strain data. Remarkably, the optical method demonstrates better measurement accuracy during the unloading stage compared to conventional strain gauge methods. At relatively high stress levels, the optical method demonstrates a relative error of less than 7% and an absolute error within 0.5 MPa. Furthermore, a comparative analysis between the optical method and the conventional contact resistance strain gauge method highlights the optical method's enhanced accuracy and stability, particularly during the unloading stage. The proposed optical stress measurement device represents a pioneering effort in the application of DIC technology to rock engineering, highlighting its potential to advance stress measurement techniques in the field.