On the technique for estimating the maximum horizontal principal stress based on the borehole failure observations.

Good understanding of the in-situ stress and rock mass strength or their relative magnitudes is essential to underground geomechanical practices. A prevailing technique for estimating the maximum horizontal stress is the integrated method combining stress polygon, borehole breakout, and drilling-induced tensile fracture. This research embraced all these elements into a nondimensionalized chart to interpret the triangle relation among the in-situ stress, rock mass strength, and failure observation for an underground cylindrical opening at any depth. One of the potential applications of the nondimensionalized chart was shown via the filed observations from a testing tunnel in the Canadian underground research laboratory. An approaching method of untangling two correlated stress components was also proposed to constrain the in-situ stress ratio under the framework of Coulomb frictional failure theory. It is proved to be highly efficient and considerably accurate by implementing the approaching method using the failure observations from the KTB borehole in German. [ABSTRACT FROM AUTHOR]