Poor performance of countermeasures on a road on an expansive clay roadbed

Abstract

An investigation into the cause of the severe longitudinal cracking on a 1 km section of a road in the North West Province of South Africa showed that this was due to the highly expansive clay roadbed. Although reasonable countermeasures had been taken which had worked elsewhere, they proved insufficient. However, the damage would probably have been worse had they not been taken. It is not usually economic ─ especially for a low volume road ─ to totally eliminate the negative effects of an expansive clay roadbed. The most that is usually attempted is to reduce them to an acceptable degree and extent. In this case the attempt was unsuccessful. The reasons of the unexpectedly poor performance appear to have included an adverse combination of factors including ponding due to rain during construction, poor lateral drainage, a thick, highly expansive and unusual clay, and an unavoidable delay in sealing the initial cracking. It was recommended that the cracks be resealed on a regular basis and the drainage improved and maintained. Nothing further could be done except at considerable expense. However, cracking continued and after 18 years the section was in a poor condition. The investigation also showed up deficiencies in the laboratory test methods used for such clays.