In general, there has been an increase in damage due to collapsible soil, probably because of the
lack of available land in many urban areas. This causes development of marginal land, which may
contain deposits of dumped fill or deposits of natural collapsible soil. Also, substantial grading can
be required to develop level building pads, which results in more areas having deep fill.
There are two common types of collapsible soil: (1) fill, such as debris fill, uncontrolled fill, and
deep fill, and (2) natural soil, such as alluvium or colluvium, as discussed below