Experimental Research on Conversion for Q-s Curves of Self-Anchored Test Piles and Construction of Conversion Formulas

The laws for load transfer and displacement of top-uplift piles, top-down piles without soil at bottoms, top-down piles with soil at bottoms and self-anchored test piles were studied by model tests in the laboratory. The results showed that Q-s curves for top-uplift piles presented a sudden drop and the curves of top-down piles without soil at bottoms prensted a slow drop. The Q-s curves of top-down piles with soil at bottoms consists of two stages, which were linear stages and nonlinear stages. The Q-s curves for the upper segment of self-anchoring test piles were of properties of top-uplift piles, while the curves for the lower segment were of properties of top-down piles with soil at bottoms. Comparing the load transfer law of top-down piles without soil at bottoms and top-down piles with soil at bottoms, it was found that the friction resistance reached to the ultimate value before the pile tip resistance. For top-down piles with soil at bottoms, the bearing capacity of single piles went through two stages. The first stage was the development stage of lateral friction resistance, which approximately corresponded to the linear stage of Q-s curves. The second stage was the development stage of pile tip resistance, which approximately corresponded to the nonlinear stage of Q-s curves. Based on the above analysis, a two-stage conversion method from Q-s curves of self-anchoring test piles to Q-s curves of top-down piles with soil at bottoms was proposed. Compared with the results of static load tests for model piles and in situ piles, the converted Q-s curves of self-anchoring test piles were highly consistent with Q-s curves of top-down piles with soil at bottoms after being conversed by the two-stage conversion method, which provided a reliable conversion method of Q-s curves for the engineering application of self-anchored test piles.