Analyses of laterally loaded piles in sloping ground are commonly performed using the conventional p-y method. The modifications made to the horizontal ground surface curves to account for sloping ground are based on several assumptions whose validity needs to be evaluated. This paper presents a series of 3D finite element (FE) analyses of a single laterally loaded pile in sloping sand and clay soils for various inclinations of the ground surface. The results of the 3D finite element (FE) analyses are compared to the results of conventional p-y analyses in which several different approaches accounting for the slope inclination are examined.
Laterally loaded offshore piles are conventionally analysed using the p-y method (API1) in which the soil is represented by a series of non-linear springs. Relationships for p-y curves for sloping ground surfaces are incorporated in most computer codes used in offshore pile design. They are based on curves determined experimentally for horizontal ground surface, such as those established by Matlock2 for clay and Reese et al.3 for sand. Modifications to the horizontal ground surface curves to account for sloping ground are commonly made either by assuming a reduced value of the ultimate soil resistance close to the ground surface or multiplying the whole p-y curve by some reduction factor4, 5, 6. These modifications have limited experimental or theoretical justification and have yet to be assessed. Four modified p-y curves are considered here, and the results of conventional p-y analyses based on these curves are compared to finite element analysis results.
A series of 3D-FE analyses were performed and are presented in this paper in order to investigate the influence of the slope angle on pile behaviour. In particular the influence on the horizontal pile displacements and the maximum bending moment is investigated. This is done through the introduction of the following two coefficients:
where yoo and yo¿ are the horizontal displacements of the top of the pile for horizontal ground surface and for slope inclination, ¿, at the same horizontal load, H, respectively, and maxMo and maxM¿ are the maximum bending moments for horizontal ground surface and for slope inclination, ¿, at the same horizontal load, H, respectively. The horizontal load-horizontal displacement curves and the calculated ry and rm values for the finite element analyses are compared with those produced by the p-y analyses.
The computer program COM624P7 was used to perform p-y analyses of a laterally loaded single pile in horizontal and sloping ground. Two sets of p-y curves, one for sand and one for clay, were used for the horizontal ground surface cases. Two modifications for each of these curves were applied to take account of sloping ground surface. The p-y curves considered are presented in the following sections.
The p-y curves proposed by Reese et al.3, and based on the field tests on piles instrumented with strain-gauges performed by Cox et al.8, were adopted in this study for the horizontal ground surface case.