Experiments with Model Piles in Groups

Abstract

Synopsis In piled foundations groups of piles are commonly used, and the piles in a group are seldom placed so far apart that they do not influence each other. Few data are available on the testing of groups in the field, because of the cost of such tests, and no satisfactory theory of group action has yet been derived. Experiments on model piles in groups in clay soil have been made to determine the influence of number, length, and spacing of piles on group-bearing capacity and settlement, and on the way in which a load is shared by piles in a model group. It was found that for square groups of given number and length of piles there was a value of pile spacing at which the mode of failure changed. For closer spacings failure was by the piles and soil enclosed within the perimeter of the group sinking as a block. For wider spacings failure was by local penetration of individual piles. The experiments on the distribution of load showed that for a large range of loading the corner piles in a group take the largest and the centre the smallest proportion of load, and that the proportion of load taken by any pile increases with its distance from the centre of the group. The results of the model tests are self-consistent, and where they touch on known or suspected properties of full-scale groups they show similarity in behaviour to what occurs in practice. Des groupements de pieux sont fréquemment utilisés dans les fondations sur pieux, et les pieux d'un groupement sont rarement placés si loin les uns des autres qu'ils n'aient pas d'influence les uns sur les autres. Peu de renseignements sont disponibles sur les essais de groupements sur chantier, à cause du coût de tels essais et on n'est encore arrivé à aucune theorie du comportement des groupements satisfaisante. On a fait des expériences sur des groupements de pieux—modèles dans des sols argileux pour dèterminer l'influence du nombre, de la longueur, et de l'espacement des pieux sur la capacité portante des groupements, de leur tassement, et de la manière suivant laquelle la charge est répartie sur les pieux d'un modéle de groupement. On découvrit que, pour des groupements carrés d'un nombre et d'une longueur de pieux donnes, il y avait une valeur d'espacement des pieux pour laquelle le mode de rupture changeait. Pour des espacements plus petits la rupture se produisait aux pieux et au sol compris dans le périmètre du groupement s'enfonçant en bloc. Pour des espacements plus grands la rupture se produisait par pénétration locale des pieux individuels. Les expériences sur la distribution de charge ont montré que pour un champ de charge important les pieux de coins d'un groupement supportent la plus grande proportion de charge, ceux du centre la proportion la plus faible, et que la proportion de charge supportée par quelque pile que ce soit augmente avec sa distance du centre du groupement. Les résultats des essais de modtèles sont réguliers entreeuxet lorsqu'ils touchent aux propriétés connues ou supposées des groupements à l'échelle normale ils montrent une similarité de comportement à ce qui se passe en pratique.

Numerical modelling of perimeter pile groups in clay

“…For the group of 16 piles, four are inner piles (25 %), thus the group of 25 piles is less efficient. Whitaker (1957) and Barden and Monckton (1970) also showed that a group of 25 piles at 2.0 d centres achieved an efficiency of about 0.8.…”

“…For the group of 16 piles, four are inner piles (25 %), thus the group of 25 piles is less efficient. Whitaker (1957) and Barden and Monckton (1970) also showed that a group of 25 piles at 2.0 d centres achieved an efficiency of about 0.8.The group spaced at 3.0 d suffers less from the effect of neighbouring piles, and the group spaced at 1.5 d suffers considerably more, with an efficiency of just 0.54 at a settlement of 0.10 d. …”

“…Numerous studies have investigated the effect of pile spacing on group efficiency, for example: Feld (1943), Whitaker (1957), Saffery and Tate (1961), Terzaghi andPeck (1967), de Mello (1969), Barden and Monckton (1970), Cooke (1974), andO'Neill (1982). Considerable testing was done as part of these previous research efforts to evaluate the influence of pile spacing on group behaviour and efficiency, yet the outcome remained somewhat inconclusive.…”

Optimizing the Bearing Capacity of Tapered Piles in Realistic Scale Using 3D Finite Element Method

“…The columns are bearing capacity of different parts of single piles. From left, the first column is pile's name; the second is total bearing capacity obtained by Davisson method (Whitaker 1957); third is total bearing capacity obtained by tangent method (Us Army Corps of Engineers 1997); fourth column shows average of total bearing capacity; the fifth one is end bearing capacity of single piles; the sixth is frictional bearing capacity of each single pile and the last column is end bearing capacity arising from inclination of tapered pile body and as can be seen, this value is zero for cylindrical pile. Tables 5, 6 and 7 show these values in sand soil with internal friction angle of 33°, 38°and 43°, respectively.…”

The equivalent pier method for energy pile groups

“…Group effects have been widely evidenced in conventional applications of piles subjected to mechanical loads when serving as structural supports for on-and offshore constructions (e.g. Whitaker, 1957;Sowers et al, 1961;Poulos, 1968;O'Neill, 1983). They have also been recently observed in innovative applications of energy piles subjected to both mechanical and thermal loads when serving as structural supports and geothermal heat exchangers for civil structures and infrastructures (e.g.…”