Accurate estimation of rock mass properties is crucial for performing a realistic Geomechanical stability analyses. This requires detailed geological information on the rock mass and jointing system, as well as, the intact rock strength. The conventional methods for strength measurement require core samples, which are expensive, have a time lag and are time consuming; and maintaining the in-situ condition and sample preparation are arduous tasks. It would be ideal if the strength of the rock could be estimated in the field as an in-situ measurement inside closely spaced boreholes. Estimation of the rock strength by scratching its surface has been reasonably successful. Application of this concept for assessment of rock strength in a borehole has led to development of a borehole strength measurement probe. The results of initial tests for development of such probe are presented and explained in this paper. In this study, four different rock samples have been used in cutting tests by a miniature disc cutter. Measured normal, rolling and side forces are recorded to allow for establishing a relationship between cutting geometry and rock strength. The results show a promising correlation between the average normal force for cutting the rock surface with a customized disc and the UCS/BTS of the rock samples with a reliable coefficient of determination. These outcomes can pave the way for the development of the field borehole probe in subsequent studies.


Estimating rock mass properties are essential input for performing geomechanical stability analysis for any structure that is constructed in rock and availability of geological information is the crucial component of such analysis. One of the important parameters in evaluating the rock mass properties is the intact rock strength. This parameter is usually measured by testing the core samples, obtained from exploration boreholes and are subsequently tested in Geomechanics laboratories. The test results offer limited information about the rock at the few locations for the borings despite all the efforts and costs. However, despite all the efforts made to prepare and test the samples, the results may not necessarily be representative of the behavior of the rock in the field since the test cannot provide the in-situ condition of the ground. The ideal solution is to estimate the rock mass properties in-situ, and inside closely placed drill holes in an underground space.

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