Down-Hole Collapse Test System

An in-situ collapse test for collapsible soils was developed. The test is conducted in a borehole with a load applied to a loading plate at the base of the hole. Water is introduced, and the load-displacement response of the soil is monitored. An analysis of the stress and the degree of wetting encountered during this test was based on a combination of field investigation (empirical data) and finite-element analyses. These studies enabled the development of a technique by which the load-displacement data, obtained from the test, can be converted to stress-strain data. Simplified charts for interpretation of the in-situ test results are presented. A series of in-situ collapse tests was performed at a site known to exhibit wetting-induced collapse. A footing test, in which collapse settlements were induced, was also performed at this site. The recommended analysis of the in-situ test was used, and close agreement was obtained between estimated footing settlement and observed settlement.