Analysis of the Interaction Between the Upper and Lower Piles in a Self-Anchored Test Pile

To quantitatively study the interaction relationships between upper pile sections and lower pile sections under the test condition of self-anchored loading, indoor model tests were conducted under three test conditions. The test conditions comprise self-anchored loading, single upper loading, and single lower loading in silty soils. By comparing the load-displacement curves, axial load transfer curves, and shaft resistance distribution curves of the upper or lower section of the pile, the effects of the lower pile loading on the upper pile and the effect of the upper pile loading on the lower pile are analyzed. The results show that when the upper or lower pile is loaded, pulling of the other pile through the soil occurs. However, in terms of the load transfer behavior and load level, the pulling influence can be ignored. Moreover, the additional stress in the soil surrounding the pile increases with load but decreases with distance. Specifically, at a distance of six times the pile diameter, the additional stress is almost zero. The distribution of additional stress caused by the self-anchored loading in the soil is highly similar to that caused by the single upper loading or single lower loading. In conclusion, the influence of the interaction between the upper and lower pile sections on the bearing capacity can be ignored when converting the bearing capacity of a self-anchored pile to the bearing capacity of a conventional static load pile.