Mitigation Measures for Small Structures on Collapsible Alluvial Soils

Abstract

The effectiveness of treatment methods for collapsible soils was evaluated under field conditions using six full‐scale load tests performed on 1.5 m square footings. Treatments included conventional methods such as prewetting with water and partial replacement with compacted fill along with more innovative procedures such as prewetting with a sodium silicate solution and dynamic compaction under dry and wet conditions. A load test was also performed on untreated soil for comparison purposes. Soil improvement was evaluated using double oedometer testing on “undisturbed” samples along with cone penetration tests and pressuremeter tests. Settlements were monitored as a function of moisture penetration and compared with predictions based on oedometer testing. Settlement of the footing on untreated soil exceeded 400 mm and differential settlement was substantial. Prewetting prior to loading did not significantly improve footing performance. Use of a compacted fill mat delayed the onset of settlement and reduced differential movement, but settlement eventually exceeded 100 mm. Although the sodium silicate and dynamic compaction methods were more expensive than conventional procedures, they prevented settlements from exceeding 25 mm.