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

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This experimental study examines the axial and oblique pullout capacity of belled piles embedded in unreinforced and geogrid-reinforced sand. The research addresses a gap in studies of long belled piles under oblique loading in reinforced soil.<br /><br />Laboratory tests used aluminium model piles with short and long embedment ratios (L/Ds = 5 and 10), a bell-to-shaft diameter ratio of 2, and sand at two relative densities. The effects of geogrid size and placement, embedment, sand density, and load inclination (0°, 30°, and 45°) were investigated. Pullout improvement was assessed using the pile capacity ratio (PCR), comparing reinforced and unreinforced beds.<br /><br />The optimum geogrid size was five times the bell diameter. For short piles, the most effective placement was directly above the bell; for long piles, it was 4.5 shaft diameters below the ground surface. Geogrid reinforcement increased pullout capacity by improving soil–reinforcement interlocking and mobilizing a wider, heavier failure zone. Capacity also increased with greater embedment and sand density, but decreased as the load inclination angle increased. Reinforcement improved capacity under both axial and oblique loading, although the additional PCR benefit from varying embedment was modest when the geogrid was optimally sized and positioned.<br /><br />The findings suggest that appropriately placed geogrid can enhance belled-pile uplift resistance, potentially allowing more economical foundation designs.

Keywords

belled piles

pullout capacity

geogrid reinforcement

oblique loading

axial loading

sand embedment

pile capacity ratio

uplift resistance

relative density

failure zone