Behaviors of shaft resistance and tip resistance of piles under different conditions and conceptualization and application of distribution of shaft resistance

According to the analysis of the results of the vertical static load tests on shaft resistance and tip resistance of 51 piles in 24 groups, the soil properties and vertical distribution, ratio of length to diameter of piles and post-grouting effect are the main factors affecting the characteristics and distribution of the shaft resistance. In soft soils, the shaft resistance of piles plays a normal function, and its distribution pattern is not affected by the ratio of length to diameter. In gravel and sand, the shaft resistance below ground about 5d depth exhibits strain softening and gradually evolves into strain hardening, which leads to the result that it lags or decreases significantly with the increasing depth. The harder the soils, or the larger the ratio of length to diameter, the more obvious the dissimilation of distribution pattern of the shaft resistance. The effect of post-grouting reinforcement on the shaft resistance of piles in the gravel and sand is far higher than that in other soils. The distribution modes of shaft resistance under working loads can be conceptualized into six types: trapezoid shape, inverted trapezoid shape, olive shape, lantern shape, garlic shape, peak and valley shape. The tip resistance ratio decreases with the increasing shaft resistance and the increasing ratio of length to diameter, and it increases nonlinearly with the increasing head loads. The values of the tip resistance ratio under working loads are given. Each conceptual mode for the shaft resistance is decomposed into rectangular and triangular distribution units associated with the pile length l and kl. Then the additional stress coefficient of Mindlin solution for settlement can be determined according to the above results. The calculated results show that except regular trapezoid shape and garlic shape distributions of shaft resistance, the integral value of the additional stress using the Geddes mode is about 15%~74% larger than that of the conceptualization shape. The higher the center of gravity of the shaft resistance, the greater the differences between the Geddes mode and the measured.