An Experimental Study of Horizontal Behavior of Group Suction Piles in Sand

Abstract

In this study, a new type of group suction pile as foundations of recently-developed massive and hybrid types of floating structures was proposed to improve the shortcomings of conventional single suction piles. Small-scale model tests were performed to investigate the better performance of the newly developed group suction pile and to estimate its horizontal behavior. To minimize the inherent limitation of small-scale model tests, the model suction piles were manufactured considering the similarity in their geometries, equivalent flexural and axial rigidities, and interface problems (in terms of relative roughness between model pile and sands). Furthermore, for more accurate component behavior analysis (in terms of vertical and horizontal movement as well as rotation) of large-displacement suction pile behavior, Particle Image Velocimetry (PIV) analysis is implemented. To secure repeatability of the experimental method and to verify the efficiency of the group suction pile, preliminary single suction pile tests were performed under various loading conditions. For the single suction pile, the effect of suction installation method on its ultimate horizontal capacity was evaluated from the model tests and the change of its ultimate horizontal capacity under various combinations of loading location and load inclination was analyzed. The test results of single suction piles were compared with the estimations based on the typically-used equations proposed by other researcher. From the group suction pile model tests, their horizontal behavior was examined for various loading locations, load inclinations, and component pile spacings. In addition, the effect of cyclic loading on the ultimate and residual horizontal resistances was analyzed. The group effect of group suction piles was assessed by measuring load distribution ratios of component piles. Strong linear relationship between ultimate horizontal capacity and pile rotation was identified for both single and group suction piles. The rotations of suction piles against horizontal loads were much smaller for group type than for single type. The horizontal resistances of single suction piles rapidly decrease and converge to zero after their ultimate capacities, while considerable residual horizontal resistances were identified for the group suction piles. The residual resistances of group suction piles range from 40% ~ 75% of their ultimate capacities. From the results of the load distributions of component piles, the horizontal resistance for a group suction pile increased with an increasing component pile spacing. Moreover, it is expected the group effect on the ultimate horizontal resistance is not significant for the group suction piles with pile spacing larger than 4 times their pile diameters. As results, the newly proposed group suction pile in this study effectively resists against horizontal loading regardless of loading location and load inclination (0 and 20 degrees with respect to the horizontal direction) without significant rotation, compared to the case of a single suction pile. Therefore, under horizontal loading conditions, the group suction piles can be considered a more favorable foundation type as a foundation of floating structures compared to the conventional single suction piles.