Abstract: Pile and soil stress calculation method for triangular arrangement pile-net composite foundation is established in this study according to the Hewlett and wedged soil arch model respectively,from which,the pile efficacy equation can be obtained.With the comparison of pile efficacy for square and triangular pile-arrangement cases,influences of pile area replacement ratio and the pile spacing are discussed accordingly.With the calculation results by the two soil arch models,applicability of the two models in triangular arrangement case is studied.Main achievements are as follows:the wedged soil arch model can be applied in the pile efficacy calculation with various embankment heights.However,the Hewlett model only can be used while the embankment height is greater than the hemispherical soil arch height.If pile area replacement ratio is same,the calculated pile efficacies for triangular and square arrangement pile-net foundation are almost completely consistent to each other,but the soil arch height for triangular arrangement condition is far below than the square one.And if the embankment height was within the range of 2.0~5.0m,calculation results of the two soil arch models also will be well coincident to each other as within a higher backfill internal angle condition.