Abstract: Geddes’s method is widely applied to estimate the settlement of pile group in China with its simple principle and easy realization. However, Geddes’s method has its own obvious shortcomings. The influence of pile diameter is not considered in Geddes’s method which can produce great stress concentration on the pile tip. Moreover, the distribution of shaft resistance of long piles under vertical working load is quite different from the suggested one of Geddes’s method. In order to solve these problems, based on Geddes’s method, a modified assumptions is presented, i.e. the end resistance uniformly distribute on the pile tip and the shaft resistance distributes on the side surface of the pile. Mathematical integration and Gauss integration are applied to estimate additional stress in the soil, which can significantly decrease the influence of stress concentration. Meanwhile, calculation formula of additional stress in the soil of bilinear distribution pattern is deduced by the combination of Geddes’s method. Case studies show that the settlement predicted by modified Geddes’s method is smaller than that predicted by Geddes’s method.

Key words: Geddes’s method, integration, shaft resistance, additional stress, settlement