In South Africa, the stiffness of dolomite residuum has traditionally been viewed as relatively low. For reasons of economy, available dolomite residuum stiffness data mostly stem from plate load tests on each of the materials forming the residual profile, typically chert gravels and wad, rather than on the actual mix of materials that typically occurs in situ. This paper presents back-calculated stiffness values from a series of large-scale surcharge trials carried out in Centurion, south of Pretoria, for the Gautrain Rapid Rail Project. It is shown that the mass stiffness of the residual dolomite profile is significantly higher than the traditionally recognized values of its constituents, allowing the viaducts for the Gautrain south of Pretoria to be founded on dolomite residuum instead of bedrock.

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