Performance of Open and Close-End Screw Piles in Bearing Layer-Paper

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This study experimentally compared open- and closed-end single-helix screw piles in dense sand, focusing on installation effort and bearing performance. Model piles were installed in dry Toyoura sand, with a dense bearing layer beneath a looser upper layer. Two installation procedures were tested: installing from the ground surface to a depth of one helix diameter (1Dh) into the bearing layer, and installing directly into the bearing layer by 1Dh. Installation load and torque were recorded, followed by compression load tests.<br /><br />When installed from the surface, open-end piles developed a substantial soil plug within the shaft. By the time they reached the bearing layer, they behaved much like closed-end piles: installation effort and load–settlement responses were similar.<br /><br />When installed directly into the bearing layer, the open-end piles remained largely unplugged. They required less installation load than closed-end piles, while installation torque was similar. They also showed a higher bearing response. The authors attribute this to soil entering the open shaft, reducing resistance beneath the shaft during installation and limiting disturbance of the soil beneath the helix. Because the helix makes a major contribution to capacity, preserving the soil beneath it may improve bearing performance.<br /><br />The results demonstrate that pile-end behavior depends on installation history and soil plugging. Open ends can offer advantages when piles enter the bearing layer without first accumulating a plug, but those advantages may diminish with deeper installation. The authors recommend further experiments to confirm these findings.

Keywords

open-end screw pile

closed-end screw pile

dense sand

soil plugging

bearing performance

installation torque

installation load

single-helix pile

compression load test

load-settlement response