静压桩桩-土界面滑动摩擦机制研究

静压桩侧阻力的实质是桩-土之间的摩擦，但其机制研究并未使用目前成熟的摩擦学理论。系统地介绍了摩擦学中黏着摩擦机制和变形摩擦机制，进而利用其分析解释静压桩桩-土界面的滑动摩擦机制，并得到较好的效果，为桩侧摩阻力的研究提供了新的思路。研究结果表明，桩-土之间的干摩擦是外摩擦；沉桩过程中桩-土之间的滑动摩擦是泥浆润滑下的湿摩擦，从而使桩侧阻力远小于载荷试验时的桩侧阻力；沉桩停顿使压桩力急剧增大的主要原因是：泥浆润滑膜的消失使桩-土之间的摩擦从湿摩擦变为干摩擦；载荷试验在桩破坏前桩-土之间的摩擦是干摩擦；桩端附近桩侧阻力强化的主要原因是：桩端土的强度提高引起桩端附近切向力的增大，从而导致桩-土之间摩擦系数提高。

Mechanism of sliding friction at pile-soil interface of jacked pile

The essence of shaft friction of jacked pile is friction at the pile-soil interface; but the mature tribology theory has not been used to study the mechanism of shaft friction yet. In this paper, friction mechanism of adhesion and deformation in tribology is introduced systematically. Using it to explain the sliding friction mechanism at the pile-soil interface of jacked pile, a good results is obtained. It provides a new approach to research the shaft friction of pile. The study suggests that unlubricated friction between jacked pile and soil is external friction, the sliding friction between jacked pile and soil is lubricated friction in mud that causes the shaft friction in the jacking process far less than that in load test. A pause during pile jacking can give rise to a sharp increase of pile jacking pressure. The principal cause for the increase of pressure is that the disappearance of the lubricating film of mud that brings the friction between jacked pile and soil from lubricated friction into unlubricated friction; the friction between jacked pile and soil in load test is unlubricated friction before failure; the strengthening of shaft friction near the tip of pile is due to the increase of tangential force caused by the improvement of soil strength underneath the pile that improves the coefficient of friction between piles and soil.