基础尺寸对碎石土地基扩底基础上拔承载力影响的现场试验研究

影响基础上拔承载能力的因素包括地基土物理力学参数及基础尺寸参数，而确定混凝土方量最小、基础上拔承载力最大的基础参数配比是基础优化设计的关键。以戈壁滩碎石土地基中的原状土扩底基础为研究对象，采用正交设计方法，以立柱直径、深宽比、扩展角为影响因素，以基础上拔承载力为分析指标，设计出9组尺寸的足尺基础。通过现场试验，获得了各试验基础的荷载位移曲线和上拔承载力值，提出了采用渐变率的概念表征荷载位移曲线的非线性变化特征，通过分析发现基础荷载位移曲线渐变率与承载能力呈负相关。结合正交试验分析结果，得出立柱直径、深宽比、扩展角3个因素中对碎石土地基原状土扩底基础抗拔承载能力的影响程度由大到小依次为深宽比、立柱直径、扩展角，表明在戈壁滩碎石土地基基础的工程设计中增加深宽比能提高基础抗拔承载能力。

Experimental analysis of the influence of foundation size parameters on the uplift bearing capacity of the spread foundation in gravel soil

The uplift bearing capacity of the spread foundation is determined by not only soil physical and mechanical characteristics but also its geometry shapes and scales. The foundation size parameters to determine the minimum quantity of concrete, and the maximum uplift bearing capacity, are key to optimize the foundation design. In order to study their effect on the uplift bearing capacity of the foundation, the undisturbed soil spread foundation in Gobi gravel soil is took as the case. Nine full size test foundations are designed, which use orthogonal test method selected column diameter, the extension angle of the foundation foot and the depth-to-width ratio as influencing factors and the uplift bearing capacity of the foundation as examining goal. The in-site static load tests are carried out in the Gobi gravel soil located northwest China. Load-displacement curves of nine test foundations are obtained and the uplift bearing capacity corresponding are concluded. An index named gradual change ratio is proposed to expressing plastic deformation characteristic of soil foundation under pull load. Meanwhile, the results of the tests show that the sensitivity sort of these geometry factors on the uplift bearing capacity is the depth-to-width ratio, column diameter, and the extension angle of the foundation foot. The conclusion achieve in this work is that adding the depth-to-width ratio in foundation design is an effective measure for improving the uplift capacity of the spread foundation in Gobi gravel soil.