Abstract:
The South African government's attempts to provide affordable, subsidised housing for
the very poor has 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 exceptionally light
and clay 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 test 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.
