Shear Demands of Rock-Socketed Piles Subject to Cyclic Lateral Loading-Article

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The study experimentally investigated whether the sharp shear-force increases predicted by p–y analyses at soil–rock interfaces occur in rock-socketed piles under lateral loading. Such predicted “shear spikes” can require congested reinforcement, making concrete placement more difficult and increasing the risk of construction defects.<br /><br />Researchers tested three large-scale, instrumented, 18-inch-diameter reinforced-concrete shafts embedded in loose sand above concrete blocks simulating stiff rock. The shafts had different transverse reinforcement: one designed for the predicted amplified shear demand, one meeting code minimum requirements, and one with minimal reinforcement. All were subjected to progressively increasing, fully reversed cyclic lateral loads until failure. The p–y analysis predicted shear-controlled failures for the latter two shafts.<br /><br />Instead, all three specimens showed similar lateral load–displacement behavior and flexure-dominated failure. Their ultimate lateral capacities exceeded the p–y-predicted failure loads for shear-deficient specimens by 53% and more than 100%, respectively. Cracking was predominantly horizontal and concentrated within about two feet above the rock socket, where a plastic hinge formed. The sockets themselves showed no observed cracking or significant lateral deformation. Measured and predicted bending-moment profiles were in reasonably good agreement.<br /><br />The findings suggest that, for the tested configuration, predicted shear amplification did not cause the expected shear failure, even when reinforcement was below that required to resist the calculated spike. This may indicate potential to reduce reinforcement congestion, but the authors emphasize that the results are preliminary: only one shaft geometry and soil-over-rock arrangement were tested, with loose sand and no axial pile load. Further testing and validated numerical analyses are needed before broader design recommendations can be made.

Keywords

rock-socketed piles

lateral loading

soil-rock interface

shear spikes

p-y analysis

reinforced-concrete shafts

transverse reinforcement

flexure-dominated failure

plastic hinge

congested reinforcement