In this study, effects of pile length and number of piles on settlement behaviour of pile groups are investigated. It is shown that the settlement of a pile group becomes independent from the number of piles beyond a certain point. Effect of pile length on settlement behaviour of the example foundation is also investigated. It is indicated that the settlement behaviour is becoming more effective in case the pile is longer. Besides, a relationship for group efficiency coefficient is suggested for estimating stiffness of a pile group using single pile stiffness by considering the interaction among piles and non-linear behaviour.


Settlement behaviour of a pile group highly depends on the number of piles and pile length. In general, settlements are reduced by inclusion of piles (Randolph, 1994). However, interaction among piles cause a reduction in the stiffness of pile groups (Fleming et.al., 2009). Stiffness reduction in a pile group due to the closely spaced piles is known as group effect. Beneficial effects of piles vanish beyond a certain number of piles due to the group effect (Poulos, 2001). One of the aims of this study is to show how the number of piles affects settlement behaviour of pile groups. This aim is achieved by introducing an example foundation. Several analyses are done for this purpose and variation of settlement with the number of piles is shown.

Effects of pile length were investigated by keeping the total quantity of piles constant. Second aim of the study is to reach the most effective solution by keeping the total cost of the construction to be constant which may be regarded as optimization. The first stage in the analysis was to decide the number of piles and pile length using capacity based design approach. After determining the pile length and number of piles for the first analysis stage, total quantity of pile by meter (Σ nl) was kept constant by changing both the number of piles and pile length. The reason of using different number of piles for the different pile length is to reach the most economical design with satisfactory foundation behaviour. Optimum design may be obtained by investigating the settlement behaviour without changing the cost of the construction. Several analyses need to be done to capture the variation of settlements with varying pile length. Finite element analysis was used for investigation of the effect of pile length. Eight different pile layouts and six different pile length were used in order to capture the variation.

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