Complete geomechanical characterization of rock mass with hydraulic borehole pressure cells

The Department of Interior’s Bureau of Mines has been actively engaged since the 1950’s in developing practical techniques to determine geomechanical factors for use in realistic design of underground structures such as mines, tunnels, and large rock caverns. These factors include the deformation modulus, Poisson’s ratio, existing in situ stresses, and the in situ strength of a rock mass. A reliable method to determine realistic in situ values for these important design parameters has remained a major issue in rock mechanics for many decades. During the past few years the Bureau has been experimenting with an innovative and practical technique to determine the in situ values of the above four parameters simultaneously utilizing a combination of three borehole pressure cells installed in one hole as shown in Figures 1. The following is a brief description of the theoretical approach: