A Review on Estimation of in Situ Rock Stress

Successful estimation of in situ rock stress field (rock stress tensor) is of paramount importance for safe and economic design as well as execution of any project within the domains of Civil Engineering, Mining Engineering, Petroleum Engineering and Geological / Geophysical research. The regional rock stress field is primarily governed by the Earth’s tectonic movements, whereas the project specific in situ stress field is controlled by overburden pressure, topography, geological structures etc. While using a geotechnical software for designing an engineering structure, in situ rock stress shares equal weightage beside rock strength parameters. Several authors have proposed different empirical relationships between overburden depth, rock density, deformation modulus to calculate the magnitude of vertical stress and ratio of average horizontal stress to vertical stress (k). Use of geological structures like fault, fold, intrusive dike, joint & fracture have also been proposed to decipher directions of principal stresses. Existence of high horizontal stress relative to vertical stress is indicated by phenomenon like core disking, borehole break out during exploratory drilling. However, in situ rock mechanical tests (Overcoring, Hydraulic Fracturing, Hydraulic Testing in Pre-existing Fractures or HTPF etc) must be performed to ascertain the magnitudes and directions of all three principal stresses, prevalent to a project site. Owing to the uncertainties associated with absolute quantification of rock stress magnitude, use of the term ‘stress estimation’ is preferred. Although the term ‘stress measurement’ is used when the stress tensor is estimated by applying aforesaid in situ rock mechanical tests.