自锚试桩Q-s曲线转换试验研究及转换式的构建

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

通过室内模型试验,研究了“顶拉桩”“顶压无土桩”“顶压有土桩”和“自锚试桩”的荷载传递及位移变化规律。研究表明:“顶拉桩”呈现突然破坏,“顶压无土桩”呈现延时破坏;“顶压有土桩”的Q-s曲线由线性、非线性两个阶段构成;“自锚试桩”上段桩Q-s曲线具有“顶拉桩”的属性,下段桩具有“顶压有土桩”的属性。对比“顶压无土桩”与“顶压有土桩”的荷载传递规律,发现桩侧摩阻力先于桩端阻力发挥。对“顶压有土桩”来说,单桩承载力经过两个发挥阶段:第一阶段为桩侧摩阻力发挥阶段,近似对应Q-s曲线上的线性阶段;第二阶段为桩端阻力发挥阶段,近似对应Q-s曲线上的非线性阶段。据此提出“自锚试桩”Q-s曲线向“顶压有土桩”Q-s曲线的两段转换法。经与模型桩静载荷试验以及原位桩静载荷试验对比,经两段转换法转换后,转换的自锚试桩的Q-s曲线高度吻合“顶压有土桩”的Q-s曲线,为“自锚试桩”的工程应用,提供了可靠的Q-s曲线转换方法。

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.