Experimental Investigation of Helical Pile Performance for Loess Deposits Improvement-Article

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The study evaluates whether installing helical piles can improve collapsible loess in Golestan Province, Iran, where wetting under load can cause severe settlement. Researchers tested dry installation (applying torque and downward crowd pressure) and wet installation (adding pressurized water), using laboratory soil tests, model piles in a Frustum Confining Vessel, and full-scale field piles.<br /><br />Laboratory tests showed that saturated loess is highly sensitive to loading: its void ratio decreased by as much as 35%, while its collapse index fell by about 77% as crowd pressure increased. This indicates substantial soil restructuring and compaction when water and pressure act together.<br /><br />For both model and field piles, bearing capacity generally increased with crowd load, pile length, and number of helices. Dry-installed piles had greater measured capacity than wet-installed piles. However, wet installation caused greater disturbance and rearrangement of the surrounding soil, producing more effective ground improvement and reducing the risk of future collapse. Wet-installed model and full-scale piles also showed broadly similar load–displacement behavior.<br /><br />The authors report that treatment reduced predicted settlement and raised the improved soil’s bearing capacity to roughly seven times that of natural loess; untreated saturated loess retained only about 4% of the bearing capacity of natural dry loess. They propose combining helical piles with narrower shallow foundations as a material-efficient approach for supporting structures on loess. Overall, the findings suggest helical-pile installation—particularly with simultaneous water pressure and crowd loading—can densify loess, lessen collapsibility, and improve foundation performance.

Keywords

helical piles

collapsible loess

Golestan Province

wetting under load

bearing capacity

soil collapse index

crowd load

wet installation

ground improvement

settlement reduction