Lateral load behavior of jetted and preformed piles

In pile installation, water jetting and preforming can be utilized as effective aids to impact driving whenever hard strata are encountered above the designated pile tip elevation. In the case of jetting, the immediate neighborhood of the pile is first liquefied due to high pore pressure induced by water jetting and subsequently densified with its dissipation. In addition, the percolating water also creates a filtration zone further away from the pile. Hence jetting invariably causes substantial disturbance to the surrounding soil which results in a notable change in the expected lateral load behavior. The first part (Chapter 2) of this dissertation presents the results of an experimental study performed with similar model piles installed using (1) impact driving and (2) jetting in a sandy soil (with 10% clay) compacted to different unit weights under unsaturated and saturated conditions. The beam theory and polynomial approximations are used to convert measured load-strain data to conventional lateral load characteristics (p-y curves). Then, the effect of jetting pressure on the lateral load behavior of piles is presented in terms of normalized design curves.; In the case of preforming (preboring), due to the removal of insitu confining stress, a substantial disturbance is caused in the surrounding soil resulting in a significant change in the lateral load behavior of driven piles. The second objective of this dissertation research was to quantify the possible reduction in the lateral load behavior of driven pile when preforming is employed as an aid to driving. The second part (Chapter 3) of this dissertation presents the results of the above described model study extended to piles preformed under different bore hole diameters. The effect of the preformed bore hole diameter on the lateral load behavior is also presented in terms of normalized design curves. In addition, a computational model that can predict the effects of preforming on the lateral load behavior of piles is also formulated. In this model, the embedded pile and the foundation soil are modeled by 8-node brick type finite elements. The pile material is considered to be elastic-perfectly plastic while the soil stress-strain behavior is represented by the Drucker-Prager cap model. Further, specially designed interface elements are utilized to accurately model the finite deformation and slipping at the pile/soil interface during lateral loading. Moreover, the effect of the diameter of the preformed borehole is incorporated by introducing the corresponding initial driving stresses computed by the cavity expansion theory. Then, the measured load-deformation behavior of preformed piles is compared to the computational predictions.; The final objective of this dissertation research was to investigate the zone of influence of jetting on existing piles. This is achieved through an additional model testing program that involved monitoring the effects of axial and lateral load characteristics of existing driven piles, due to jetting of other piles at designated locations in the neighborhood. The results indicate that the influence of jetting extends up to about five times the pile diameter with respect to the lateral load characteristics.