急速增湿条件下湿陷性黄土中桩基的承载性状

入渗增湿条件下,湿陷性黄土地区中桩基的承载性状会因桩周土基质吸力减小和湿陷变形而显著劣化,进而诱发一系列的工程问题。为了研究浸水前后湿陷性黄土中桩基承载性状的变化规律,进行模型桩的入渗试验,同时对桩周土体的变化（包括沉降、体积含水率、基质吸力）以及桩基承载性状的变化（包括桩顶沉降、桩侧摩阻力和桩端承载力）进行监测。将入渗过程中桩周黄土基质吸力变化与桩基承载性状的变化相关联,从非饱和土力学的角度阐明入渗前后桩基承载性状的变化规律和变化机理。研究结果表明,入渗过程中的桩顶沉降和桩端承载力不断增加,桩身轴力大致呈“ D ”型分布,最大轴力出现在入渗过程中。入渗过程中桩周黄土的基质吸力减小,产生湿陷变形,使桩侧摩阻力大小和方向发生改变,进而导致桩基承载性状的变化。基于非饱和土力学原理对传统的剪切位移法进行简化和修正,提出考虑桩周黄土湿陷变形影响的单桩沉降预测模型,并结合试验结果对理论模型进行验证。本文的研究成果有助于进一步完善复杂环境荷载作用下湿陷性黄土地区的桩基设计理论和工程性状评估。

Mechanical Behavior of Pile Foundation in Collapsible Loess upon Rapid Infiltration Condition

Upon infiltration, the mechanical behaviors of pile foundations in collapsible loess areas will deteriorate significantly due to the reduction of soil matric suction and collapsible deformation, which will lead to a series of engineering problems. In order to study the changes in the bearing behaviors of pile foundations in collapsible loess before and after infiltration, infiltration tests of model piles were carried out. The changes in the soil around the pile (including settlement, volumetric moisture content and matric suction) as well as the changes in the mechanical behaviors of pile foundations (including the pile head settlement, pile shaft friction and pile base resistance) were monitored. The changes in soil matric suction around the pile perimeter during infiltration were correlated with the changes in pile foundation bearing properties to elucidate the changes in pile foundation bearing properties before and after infiltration based on unsaturated soil mechanics. Research results show that the pile top settlement and pile end bearing capacity increase continuously during the infiltration process, and the pile axial force is roughly distributed in a "D" shape, with the maximum axial force appearing during the infiltration process. During the infiltration process, the matric suction of the loess around the pile decreases, resulting in collapsible deformation, which changes the magnitude and direction of the pile lateral frictional resistance, thus leading to changes in the bearing properties of the pile foundation. Based on the principle of unsaturated soil mechanics, the traditional shear displacement method is simplified and modified, and a single pile settlement prediction model is proposed to take into account the effect of collapsible deformation of the pile foundation. The theoretical model is validated with the experimental results. The research results of this paper help to further improve the design theory and engineering property evaluation of pile foundation in collapsible loess areas under complex environmental loads.