MITIGATION MEASURES FOR SMALL STRUCTURES ON COLLAPSIBLE ALLUVIAL SOILS

The effectiveness of treatment methods for collapsible soils was evalu ated under field conditions using six full-scale load tests performed on 1.5 m square footings. Treatments included conventional methods suc h as prewetting with water and partial replacement with compacted fill along with more innovative procedures such as prewetting with a sodiu m silicate solution and dynamic compaction under dry and wet condition s. A load test was also performed on untreated soil for comparison pur poses. Soil improvement was evaluated using double oedometer testing o n ''undisturbed'' samples along with cone penetration tests and pressu remeter tests. Settlements were monitored as a function of moisture pe netration and compared with predictions based on oedometer testing. Se ttlement of the footing on untreated soil exceeded 40() mm and differe ntial settlement was substantial. Prewetting prior to loading did not significantly improve footing performance. Use ot a compacted fill mat delayed the onset of settlement and reduced differential movement, bu t settlement eventually exceeded 100 mm. Although the sodium silicate and dynamic compaction methods were more expensive than conventional p rocedures, they prevented settlements from exceeding 25 mm.