: The acoustic emission and deformation rate analysis methods are attractive techniques for measuring in-situ rock stress because of their ease and low cost. We applied these methods to determine the vertical stress distribution around a drift excavated in soft sedimentary rock at the depth of 140 m. The variations of vertical stress around the drift were compared with those determined from an over coring method and a calculation by a finite element method program, ANSYS. We also tried to determine the stress on a rock specimen of the same type but at a shallow depth of about 35 m. The result is compared with the value estimated from the rock density and its depth, and we discuss the applicability of the acoustic emission method to detecting a very small stress level. We show an example of the limits of the methods as well as their excellent performance.
1 INTRODUCTION
In-situ rock stress measurement is an important task for the analysis and design of underground excavations because the stability of underground structures must be evaluated to avert failure or collapse of underground openings. Although many conventional techniques, such as the over coring and hydraulic fracturing methods, are used to determine in-situ rock stress, they are difficult, time consuming and expensive.
