大直径薄壁灌注筒桩土芯对承载性状影响的试验及其理论研究

RESEARCH ON INFLUENCE OF SOIL CORE ON LOAD BEARING CHARACTER OF LARGE-DIAMETER TUBULAR PILE USING CAST-IN-SITU CONCRETE

筒桩土芯性状复杂,土芯对单桩竖向承载力作用机理尚不明确,当前筒桩承载力计算还不成熟。通过试验手段,从土芯高度及土芯力学性状两方面来分析土芯对单桩竖向承载性状的影响,对新型薄壁灌注筒桩竖向承载性状进行了研究。根据土芯顶端分担荷载与否把筒桩结构分为两类,并分别对筒桩内侧摩阻力产生机理进行分析,核心是土芯与筒桩存在相对位移趋势以及相对位移的发生是筒桩内侧摩阻力产生的原因,假设内侧摩阻力随深度减小呈指数函数形式衰减;在此基础上得出了筒桩内侧摩阻力以及土芯顶端分担荷载的计算方法。试验研究与理论研究结果表明,土芯的存在对提高单桩承载力及减少沉降有较大贡献。根据试验及对土芯性状进行分析,建立了筒桩竖向承载力计算公式,工程实践证明了其实用性。

Owing to the complexity of soil core character, the calculation of bearing capacity of tubular pile isn＇t mature and the operation mechanism of single pile bearing capacity is not clear yet. A test study example is introduced and the Q-S curve is gotten from the test. From two aspects of soil core height and its mechanical characteristics, the influence on load bearing character of large-diameter tubular pile using cast-in-situ concrete is studied. According to whether the top soil core bears load or not, the tubular pile structure is classified into two types to analyze the mechanism of inside friction. The reason for the occurrence of inside friction is that the relative displacement or the trend of it exists between the soil core and pile. By assuming that the inside friction changes in minus exponential function, the method for load distribution between inside wall of pile and the top soil core is established. The result indicates that the core contributes much to enhance pile bearing capacity and to decrease pile settlement. At last, the calculation formula of vertical bearing capacity of tubular pile is established, which is proved to be practicable in projects.