端承型静压桩沉桩贯入过程中桩侧阻力变化规律及其时效性试验研究

静压桩承载力的时效性主要由桩侧摩阻力的时效性引起,沉桩结束时桩侧摩擦的性状及其发挥程度将直接影响承载力的时效性。但是,目前承载力时效性的研究直接用终压力和承载力进行相关性研究而未考虑这一影响。因此本文将选择珠三角典型地层,进行模型桩的静力压入试验及其后的载荷试验,从摩擦学的角度研究桩端阻力变化对桩侧摩阻力发挥的影响机理,并进一步研究其对承载力时效性的影响。研究表明,沉桩过程中沉桩速度因桩压入不同性质土层、局部硬层及较硬的桩端持力层而发生变化,桩土之间的摩擦状态不断在干、湿摩擦之间转变,桩侧摩阻力的发挥随之变化。终压时桩侧若为干摩擦,则承载力时效性不明显,若为湿摩擦则时效性显著,即可利用终压时桩侧摩擦的性质和发挥程度来判断单桩承载力的时效性。

Experimental Study on Variation and Time Effect of Shaft Resistance of Jacked Pile Installation

Time-dependent capacity increase of jacked piles is caused by the timeliness of shaft resistance and is affected directly by the character and mobilization of shaft resistance at the end of pile installation. However, the previous researches on the time-dependent capacity always relies on the correlation study between the pile installation resistance and its bearing capacity tested by load test, while the influence of the total shaft resistance at the end of pile installation on timeliness has been seldom considered . In this paper, jacking installation tests of model piles and load tests after installation are conducted to study the influence of base resistance on shaft resistance and further influence on the timeliness of bearing capacity of jacked pile with the theory of tribology in the Pearl River Delta. The study reveals that the friction at the pile-soil interface changes between lubricated friction and unlubricated friction during the whole pile installation. This phenomenon is caused by the change of installation velocity of the jacked pile when inserting different soil layers. If the pile shaft friction is unlubricated friction, then there is almost no time dependent capacity increase, if the pile shaft friction is lubricated friction, then the timeliness of bearing capacity is very significant. That means the shaft friction condition of pile can be used to prediction the timeliness of bearing capacity.