Footing with Settlement-Reducing Piles in Non-Cohesive Soil
Although the design concept based on the idea of limiting the settlement of footings by settlement-reducing piles is gaining more and more support, there have been very few experimental studies of the behaviour of piled footings in non-cohesive soil. The influences of the contact between the pile cap and the soil on the capacity and the load-settlement behaviour of a piled footing are considerable but this has not been well understood.
The purpose of this study is to clarify the overall interaction between the piles, the cap, and the soil in piled footings with friction piles in non-cohesive soil. The major part of the study consists of three extensive series of large-scale field model tests on single piles, free-standing pile groups, shallow footings and piled footings. The field tests were carried out in loose to dense sand, and with pile spacings of four, six and eight times the pile width. By performing the field model tests, the Author has tried to create a better understanding of the load-transfer mechanism and of the load-settlement behaviour of a piled footing in non-cohesive soil. The most important factors influencing the behaviour of piled footings have been investigated.
The study shows that in cap-pile interaction, the increase in the pile shaft resistance is most important and more pronounced than the increase in the pile base resistance and the change in the cap capacity. It is also found that the load-settlement behaviour of the cap in a piled footing is very similar to that of a shallow footing with the same geometry under equal soil conditions. This remark is used as the basis for the proposed simplified methods of predicting settlement of a friction piled footing in non-cohesive soil. The results calculated using the proposed methods are in good agreement with the measured values.
The reduction in settlement of a piled footing, in relation to a corresponding shallow footing, depends clearly on the relative cap capacity. With a high value of the relative cap capacity, i.e. when the capacity of the cap is predominant over that of the piles, the contribution of the piles has a clear effect in reducing the settlement of the footing.