Experimental Study on Axial Pullout and Oblique Pullout Capacity of Belled Pile Embedded in Geogrid Reinforced Sand Bed-Paper

Paper

Pdf Summary

This experimental study investigated the axial and oblique pullout capacity of belled piles embedded in geogrid-reinforced and unreinforced sand. Thirty model tests were conducted in a laboratory tank using sand at relative densities of 30% and 60%. The piles had embedment ratios of 5 or 10, a bell-to-shaft diameter ratio of 2, and were tested at load inclinations of 0°, 30°, and 45°. The researchers also examined geogrid size and placement.<br /><br />A geogrid measuring five times the pile-base diameter (5D) provided the greatest capacity. Its optimal position was directly above the bell for short piles (embedment ratio 5), and 4.5 shaft diameters below the ground surface for long piles (embedment ratio 10).<br /><br />Geogrid reinforcement substantially improved pullout resistance. For example, the short pile’s axial capacity increased from about 139 N in unreinforced sand to about 315 N in reinforced sand. Capacity also increased with greater sand relative density and pile embedment. In contrast, increasing the load inclination from 0° to 45° reduced ultimate pullout capacity; for a reinforced short pile, it fell from approximately 315 N to 259 N.<br /><br />The findings indicate that appropriately sized and positioned geogrid can improve belled-pile performance under both axial and oblique uplift loads. The study’s small-scale model tests provide guidance for further research and design, though full-scale validation is needed.

Keywords

belled piles

pullout capacity

geogrid reinforcement

axial uplift

oblique loading

sand relative density

embedment ratio

pile foundation

laboratory model tests

geotechnical engineering