基于Hewlett理论的支护桩桩间距计算方法研究

基坑支护桩桩间距设计通常基于经验取值,并不考虑土拱的作用和桩间土的稳定性。基于Hewlett理论分析了基坑支护桩桩间土拱效应,并开展了对桩间土整体稳定性的研究,分别得出了满足两种稳定条件的桩身荷载分担比公式和桩间距公式。通过对设置在四种土质中的支护桩桩间土拱的计算分析发现:对于强度指标较高的黏土、粉土,桩宽比为0.5时,荷载分担比即达到100%,而对于强度指标较低的淤泥质黏土,桩宽比为0.8时,荷载分担比方达到100%;桩间土整体稳定性对于桩间距的要求较为宽松。对于常规桩径的支护桩,桩间距的设计应按土拱稳定为控制准则,但对于设置在内摩擦角较大而黏聚力较小土层中的大直径桩,应按桩间土整体稳定为控制准则。

A calculation method of pile spacing based on Hewlett soil arching theory

In engineering design, the soil arching and the entire stability of the soil mass between the soldier piles are usually neglected. The research was carried out on the soil arching and the entire stability of soil mass between the soldier piles in excavation. Expressions of the loading ratio and the spacing of the piles were obtained. Through the verification in four types of clays, it is found that in the silt and clay with higher strength index, the loading ratio reaches 100% when b/S is up to 0.5; where b is width of pile cross-section; S is pile spacing; and in the mucky clay with lower strength index, the b/S should be 0.8 for the 100% loading ratio. The pile spacing can be relatively wider under the condition of the entire stability of soil mass. For the pile with regular diameter, the pile spacing should be designed meeting the stability of the soil arching, while in silt with higher friction angle but lower cohesion, especially for the piles with large diameter, the pile spacing should be designed according to the entire stability of the soil mass between piles.