Characterization of a faulted rock mass for a dam foundation

The paper analyzes the mechanical properties of a metamorphic rock mass (metabasite) at a prospective dam site. The formation is crossed by largely persistent and wavy major shears filled with a cataclastic material. The structural setting was reconstructed through scanline surveys. Surveys included detailed measurements of local orientation of the discontinuity walls and infilling thickness. Since the mechanical behaviour of the rock mass is largely influenced by the infilling material, this was carefully sampled on site. Where sampling conditions were particularly favourable, undisturbed specimens were directly retrieved from the gouge material. Laboratory tests on the infilling material included: grain-size distributions and direct shear tests on both undisturbed and reconstituted specimens. A limited number of large-scale in situ shear tests on filled discontinuities were carried out. Field geophysical investigations and rock quality estimates through the survey of exposed rock faces are also reported and discussed. Significance of shear strength parameters at dif-ferent scales has also been evaluated by comparing shear strength results from small scale laboratory tests and in situ tests.