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.
