HELICAL PILES PERFORMANCE IN GOLESTAN LOESS DEPOSITS VIA FULL-SCALE AND PHYSICAL MODELING TESTINGS-Paper

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The study evaluates whether installing helical piles can improve collapsible loess in Iran’s Golestan Province, where wetting and loading have caused severe settlement and infrastructure damage. Researchers examined soil properties and pile performance using laboratory tests, eight model piles installed in the FCV-AUT physical-modeling vessel, and four full-scale, single-helix piles installed at a 3 m depth in the field.<br /><br />Piles were installed either dry, using torque and crowd force, or wet, with water injected during installation. Laboratory tests on undisturbed and remolded samples showed that wetting combined with loading substantially reduced loess void ratio and collapse potential, while increasing density and friction angle. Water alone weakens the soil’s particle bonds, but simultaneous wetting and crowd loading densifies and rearranges the soil, improving its shear-strength characteristics.<br /><br />For model piles, bearing capacity increased with crowd force under both installation methods. Comparisons between laboratory and field results showed that their load–displacement behavior became similar under high crowd stresses. Similarity was also achieved at lower crowd stresses when water pressure was applied during installation. The authors attribute this to greater disturbance of the loess structure, making the laboratory soil behave more like natural deposits.<br /><br />The results suggest that helical-pile installation can both provide foundation support and improve the surrounding collapsible loess. Applying crowd force together with water during installation is an effective means of modifying the soil, and physical modeling can reproduce field pile behavior under appropriate installation conditions.

Keywords

helical piles

collapsible loess

Golestan Province

settlement mitigation

soil improvement

bearing capacity

wetting and loading

physical modeling

crowd force

load-displacement behavior