Lateral Resistance of Piles near Vertical MSE Abutment Walls

Abstract

Full scale lateral load tests were performed on eight piles located at various distances behind Mechanically Stabilized Earth (MSE) walls. The objective of the testing was to determine the effect of spacing from the wall on the lateral resistance of the piles and on the force induced in the MSE reinforcement by the pile load. Lateral load-displacement curves were obtained for the test piles at various spacings and with various reinforcement ratios (reinforcement length, L divided by wall height, H). Reinforcements involved both welded wire grids and ribbed straps. The force in the reinforcements was measured using strain gauges. As the pile spacing behind the MSE wall decreased, the lateral pile resistance decreased substantially. However, by increasing the reinforcement length the reduction in lateral resistance was arrested to some degree. Lateral load analyses were performed to determine the minimum spacing required to eliminate any effect of the wall on the pile resistance and the reduction in soil resistance as a function of normalized distance and reinforcement length. Little pile-wall interaction was observed for piles located more than 4 to 6 pile diameters behind the wall depending on the reinforcement. The induced force in the reinforcements increased as lateral load increased and decreased rapidly with transverse distance relative to the direction of loading. Separate upper bound design curves were developed for the welded wire grids and the ribbed strips which can be used to compute the increased force in the reinforcement produced by the laterally loaded pile. The testing to date has allowed us to develop a framework for understanding the complex interaction between the wall panels, the reinforcements, and the soil resistance against a pile based on the spacing of an abutment pile behind an MSE wall. Tentative design curves have been developed based on the limited available testing to date. However, additional testing is necessary to define behavior for lower L/H ratios typical of static conditions and to refine relationships for determining p-multipliers and induced reinforcement forces. This testing is expected to be performed as part of an upcoming pooled-fund study.