The determination of rock mass modulus variation with depth for weathered or jointed rock

Weathering or the variation in frequency and tightness of joints may result in an increase in mass modulus with depth for some rocks. This increase in modulus will continue until a depth is reached at which the rock behaves as a sound intact unit and the modulus will be relatively constant with depth below this point. In this paper, elastic solutions are presented for the deformation of such a rock mass due to a uniform or approximately rigid circular loading. Two procedures are described for determining the rock mass modulus profile from plate load test results. The first procedure uses the results from three plate tests to infer the variation in modulus with depth. The second procedure uses the measured variation in displacement with depth below a single plate to infer the mass modulus variation. 'The application of the two procedures is illustrated by a worked example and by consideration of a field case where the inferred modulus is shown to be in good agreement with alternative modulus variation data.