Strength and Deformability of Highly Fractured Rock

by Jerome M. Raphael, (F.ASCE), Prof. of Civ. Engrg.; Univ. of California at Berkeley, Berkeley, Calif.,
Richard E. Goodman, (M.ASCE), Prof. of Geological Engrg.; Univ. of California at Berkeley, Berkeley, Calif.,

Serial Information: Journal of the Geotechnical Engineering Division, 1979, Vol. 105, Issue 11, Pg. 1285-1300

Document Type: Journal Paper


This paper reviews procedures used to determine properties of the greywacke sandstone forming the foundation of a concrete dam. Multistage triaxial testing of carefully reassembled core specimens provided a series of shear-strength versus normal-stress curves for fractured rock; the lowest of these was adopted as representative of the strength of the rock mass. Deformability was measured during the triaxial tests and in the field using a borehole jack in 3-in. (76-mm) drill holes. The latter yielded a value for the normal stiffness of the fractures in the rock. Introducing this stiffness value together with any given fracture spacing then determined the rock-mass modulus of elasticity corresponding to the assigned fracture spacing. Longitudinal and shear-wave velocity measurements in cross-hole configuration determined modulus of elasticity values considerably higher than those measured with the borehole jack, as expected in fractured rock.

Subject Headings: Triaxial tests | Rock masses | Strength of materials | Deformation (mechanics) | Cracking | Rocks | Dam foundations | Concrete dams

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