Apparatus and Procedure for an In Situ Collapse Test

Procedures for plate load testing in both shallow pits and at the bottom of a borehole are presented with descriptions of the required apparatus. The procedures were developed for collapsible soils but are expected to be useful for swelling soils as well. A key feature of the new procedures is that the wetted bulb of soil under the plate is controlled and its depth is measured at the end of the test. This makes it possible to limit the range of strains in the wetted zone and to calculate the average strain. Research by the authors presented elsewhere led to the development of influence factors that allow computation of the average stress in the wetted zone. The average stress versus average strain derived from the test for the wetted condition is of the same form as that derived from a laboratory collapse test. The in situ collapse tests presented possess certain advantages over lab tests including (a) lesser disturbance effects, (b) the ability to test difficult-to-sample soils, and (c) a degree of wetting likely to be close to that achieved in the prototype. The required apparatus is simple and can be constructed at low cost by most geotechnical firms.