Abstract:
The South African Government’s attempts to provide affordable, subsidized housing
for the very poor have suffered from a large number of structural failures, many due to
heaving foundations. These houses are particularly susceptible to damage by heaving
clay because they are relatively light and clay heave can lift them very easily. Rational
design requires knowledge of the pattern of heave which will occur under the
foundation. The pattern of heave depends on the pattern of moisture movement.
Currently available methods of rational design rely on assumptions about the shape
of the mound which will develop due to moisture movement under the foundation. The
shape assumed is largely guided by measurements made on mock foundations.
Instrumentation has been installed under a Government Subsidy house in the Free
State and moisture movement is being monitored. The actual pattern of moisture
movement observed is substantially different to what is normally assumed and could
point to more reliable estimates of the heave which needs to be designed for.
