Abstract

Steeply dipping rockhead and cavities provide extreme challenges for design and construction of foundations in karst dolomite terrain. The Gautrain Rapid Rail Link will connect Johannesburg, Pretoria and the OR Tambo International Airport along approximately 80 km of align-ment with 10 railway stations. Approximately 15 km of the alignment is underlain by dolomite with nearly 6 km elevated on a viaduct. To facilitate detailed design and choice of foundation method for the viaducts founded in dolomitic bedrock or overlying residual soils the Bombela Civils Joint Venture opted to include single-hole reflection borehole radar surveys as part of the ground investigation works. First arrival time, signal attenuation and reflectors were assessed from radargrams to locate karst structures and geological discontinuities for distances up to 12 ms around each borehole. This paper describes procedures together with examples demonstrating the merit of borehole radar surveys combined with conventional ground investigation in karst dolomite.

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