Finite element modelling of undrained vertical bearing capacity of piles adjacent to different types of clayey slopes

Abstract

The bearing capacity of shallow foundations on slopes is commonly calculated from the existing design charts or using empirical equations. This paper presents the results of numerical studies carried out on the behaviour of piles located near soft, medium and stiff clay slopes under undrained vertical loading conditions. A series of three-dimensional numerical analyses were performed for various pile geometries, and different distances of the pile from the slope. The analyses have also been conducted for slopes with different angles. The obtained results show that, as the pile embedded length increases, the full formation of the failure wedge is more probable to occur in the soil and, therefore, a greater axial capacity of the pile will be mobilised. In addition, by decreasing the distance of the pile from the slope crest, the lateral movement of soils increases and the lack of soils on the slope side of the pile tends to reduce the bearing capacity. Furthermore, increasing the slope angle increases the pile lateral displacement and, therefore, the resulting eccentricity of the axial load on the pile produces more additional bending moments in the pile and consequently the axial capacity reduction increases. For practical proposes, the results of the analyses are presented in the form of design charts showing the associated reduction factors (RF) of the ultimate bearing capacity of the horizontal ground condition. It was concluded that, to obtain a RF = 1.0 (i.e. equivalent to the horizontal ground condition), it is necessary to place the pile in a distance larger than 4B from the crest of the slope, where B is the diameter of the pile.