An improved method for estimating in situ stress in an elastic rock mass and its engineering application

Abstract

The main contribution of this paper is to develop a method to determine the in situ stress on an engineering scale by modifying the elasto-static thermal stress model (Sheorey's model). The suggested method, firstly, introduces correction factors for the local tectonism to reflect the stress distribution difference caused by local tectonic movements. The correction factors can be determined by the least-squares approach based on laboratory tests and local in situ stress measurements. Then, the rock elastic modulus is replaced by rock mass elastic modulus so as to show the effect of rock discontinuities on the in situ stress. Combining with elasticity theory, equations for estimating the major and minor horizontal stresses are obtained. It is possible to reach satisfactory accuracy for stress estimation. To show the feasibility of this method, it is applied to two deep tunnels in China to determine the in situ stress. Field tests, including in situ stress measurements by conventional hydraulic fracturing (HF) and rock mass modulus measurements using a rigid borehole jack (RBJ), are carried out. It is shown that the stress field in the two deep tunnels is dominated by horizontal tectonic movements. The major and minor horizontal stresses are estimated, respectively. Finally, the results are compared with those derived from the HF method. The calculated results in the two tunnels roughly coincide with the measured results with an average of 15% allowable discrepancy.