Distribution of shaft resistance of long piles and additional stress of foundation and their influences on settlement calculation of group piles

The measured data show that the distribution of shaft resistance of long and super long piles under vertical working load is quite different from the suggested one by Geddes' solution. The shaft resistance is first fully mobilized at the upper part of the long and super long piles under the working load. Based on the measured shaft resistance distribution of the long and super long piles, both the simplified bilinear and the trilinear patterns of the shaft resistance are suggested. The additional stress solutions of the bilinear and the trilinear distribution patterns are deduced by using the combination of Geddes' solution. The comparison between the solution of the proposed patterns and the Geddes' solution shows that the additional stress beneath the piles of the Geddes' solution is significantly greater than that of the proposed method. So the settlement ratio of Geddes' solution is greater than that of the proposed method and thus the Geddes' solution overestimates the interaction of group piles. Through the back analysis of case studies, it is found that the settlement predicted by the proposed method is closer to the measured one compared with that predicted by the Geddes' solution.