砂土地基小直径单桩的浅层土p–y曲线

小直径桩在桩基础的抗震设计、加固中已得到越来越多的应用。针对美国石油协会(API)规范的p–y曲线法和中国规范的m法对小直径单桩的适用性问题,通过拟静力试验研究了砂土地基小直径单桩的浅层土(深度小于1 m)p–y曲线。对实测桩身弯矩采用分段函数的拟合方法来推算土反力和桩身变形,获得了小直径单桩在饱和中砂中的浅层土静力p–y曲线,并基于试验结果提出了三线性本构。进一步地,通过数值模拟分析比较了所提出的浅层土三线性p–y曲线、API规范的p–y曲线、中国规范的m法对预测小直径桩基受力和变形的有效性。结果显示API规范的p–y曲线可能稍低估桩基的水平承载力,并获得更深的桩身最大弯矩位置,而提出的浅层土三线性p–y曲线可更好地预测桩基的整体水平力和位移关系、桩身弯矩及变形。另外,传统的m法仍然适用,当桩身变形较小时(土面桩身变形不超过6 mm),m值宜取推荐范围内的较大值,而当桩身变形较大时,m值宜取推荐范围内的最小值。

Shallow-layer p-y curves for single micropile in sands

Micropiles are increasingly used in seismic design or retrofitting for pile foundations. This study aims to investigate the validity of the widely used p-y relationships proposed by the American Petroleum Institute (API) and the ‘m method'; in the Chinese Code for numerical modeling of micropiles in sands. A quasi-static test is performed to reveal the shallow-layer (depth less than 1.0 m) experimental p-y curves for the micropiles in saturated medium dense sands. A piecewise-function based p-y derivation method is adopted to develop the experimental p-y curves. Subsequently, trilinear models for the shallow-layer p-y curves are proposed based on the test results. Further, numerical simulation techniques are used to analyze the validity of the proposed trilinear p-y model, API p-y model and ‘m method'; for predicting the strength and deflection of micropiles in sands. The results show that the API p-y model may slightly underestimate the lateral strength and overestimate the depth-to-maximum bending moment, whereas the proposed shallow-layer trilinear p-y model preferably predicts the global force-displacement relationship, bending moment and lateral deflection of micropiles. In addition, the conventional ‘m method'; is capable to predict the strength and deflection of micropiles. Specifically, a relatively large m value chosen from the recommended range is reasonable for the situation of deflection of small piles at soil surface (less than 6 mm), whereas for the micropiles with a relatively large deflection, the smallest m value among the recommended range is a preferable choice.