Exploration of Measurement Methods of 3D In-Situ Stresses in Rock Masses

This paper gives an overview of the measurement methods for the 3D in-situ stresses. Rock masses in the Earth’s crust are stressed in a natural stress state, which has six components in three dimensions. They are called “in-situ stresses” or “field stresses” with three principal stress components. Reliable estimate of the in-situ stresses in the rock mass is essential and vital for proper planning and design, underground excavation, mineral resource exploitation and ground stability control in geotechnical, mining and petroleum engineering. The basic principles of the measurement methods, including overcoring, hydraulic fracturing, back analysis, borehole slotting, flat jack, geophysical, and borehole breakout, are introduced. The advantages and limitations are discussed and compared. Methods that measure borehole deformation and strains during overcoring appear most common and are the only methods for the complete 3D stresses. Other measurement methods generally provide results of the orientations and/or magnitudes of some components of the in-situ stresses, mostly the maximum and the minimum stresses in the plane perpendicular to the borehole. In some methods the vertical stress is assumed as a principal stress.