WJ Hewlett, MA & MF Randolph, MA, PhD, M.I.E.Aust. This paper was first published in GE’s April 1988 edition.
Embankments constructed on soft soil often lead up to structures such as bridges, that are founded on piles. Movement of the structure will be limited by the piled foundation, whereas the embankment may settle significantly and cause lateral spreading of the subsoil. Two separate problems then arise. Firstly, the piled foundation of the structure will be subjected to large lateral pressures from the subsoil, perhaps leading to failure of the piles. Secondly, differential settlements between the structure and the embankment will build up, requiring subsequent raising of the embankment.
One method of avoiding these problems is to use a grid of piles to support the embankment in the vicinity of the structure. For economic reasons no slab is used and the piles need to be placed at relatively wide spacings; the question then arises as to the proportion of the embankment load carried by the piles.
The paper addresses this question. The paper presents an analysis of the arching action of granular embankment fill overlying a rectangular grid of pile caps. The analysis is based on experience gained from laboratory model tests. Expressions are developed giving the degree of support offered by the pile caps in terms of the geometry of the piles and the properties of the embankment. Comparisons with measurements from field and model tests show good agreement with the results of the analysis.