INFLUENCE OF SURFACE REPLACEMENT LAYER ON BEHAVIOR OF LATERALLY LOADED LARGE BORED PILES IN SOFT CLAY: PILE LOAD TESTS AND NUMERICAL INVESTIGATION-Paper

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The study examines whether replacing weak surface clay with compacted sand improves the lateral resistance of large bored piles. Two 0.8 m-diameter piles in soft-to-firm clay were tested: one in natural ground and one with the upper 1.5 m replaced by compacted sand. The field-test results were used to calibrate a three-dimensional finite-element model, which was then applied to investigate the effects of replacement-layer thickness and horizontal extent.<br /><br />The replacement layer substantially improved pile performance. At a lateral displacement of 8 mm—1% of the pile diameter—the load carried increased from 106 kN in natural soil to 225 kN with replacement, an increase of about 112%. At the maximum test loads, the untreated pile displaced 21.55 mm under 170 kN, while the improved pile displaced 8.46 mm under 225 kN.<br /><br />Numerical analyses showed that pile behavior generally improved as the replacement layer became thicker or extended farther from the pile. However, benefits from increasing horizontal extent diminished beyond about 10 pile diameters, and gains from increasing thickness also became less pronounced beyond approximately 1.5 m for the conditions studied. The improved surface layer increases passive soil resistance and constrains movement near the pile head; it can also increase the maximum bending moment and shift the location of maximum shear force down the pile.<br /><br />The findings indicate that compacted-sand surface replacement can be an effective way to enhance lateral pile resistance. Its effectiveness depends on both the layer’s dimensions and the strength contrast between the replacement material and the surrounding natural soil.

Keywords

lateral resistance

bored piles

compacted sand

surface clay replacement

pile performance

finite-element model

passive soil resistance

horizontal extent

replacement layer thickness

bending moment