عبدالرضا فاضلی

Collapsible soils which have open structure with weak interparticle bounds are kinds of problematic soils. These soils show high strength when unsaturated. But as soon as reach to saturation zone, show a dramatic subtraction in volume. Sudden decrease in volume consequently generates problems for structures built on them. To avoid volume subtraction collapsible soils can be modified and reinforced. One reinforcement method proposed by geotechnical engineers is to add additives to collapsible soil. Generally, nanoparticles are among the most favored additives that have been used by engineers. In this study nanoclay has been used in order to modify collapsible soil of Sivand dam. Pressure plate apparatus has been used to investigate the effects of nanoclay particles on Water retention Curve of the collapsible soil. Water retention Curve exhibits the correlation between soil’s moisture and its inward suction for unsaturated soils. Water retention Curve has great value in examining the behaviors of unsaturated soils. Totally twenty seven experiments have been done, nine of which were on natural soil and eighteen were on modified soil with nanoclay particle additive. Mixing process has been done by a method which fazeli and his colleagues had used called wet method, sample compaction has been done statically. Examination’s variables were initial weight moist percentage, initial density, and nanoclay weight percentage. The parameters were chosen such that facilitate samples fall in the dry area of the compaction curve because the collapsing potential is more in dry area than in wet area. The study illustrates that by using four percent of nanoclay particles, collapsible soils will gain nine percent increase in water retaining capacity. Study also concluded that there exist fundamental differences between collapsible soils and any other types of soil around the Water retention Curve median zone.