基于静力触探试验的基坑开挖卸荷单桩水平承载力损失预测研究

选取典型成层地基场地并设计试坑开挖卸荷试验,开展了基于静力触探(CPT)测试的基坑开挖卸荷单桩水平承载力损失程度预测研究。通过在试坑开挖卸荷前后进行CPT原位测试,得到了试坑开挖卸荷前后的CPT贯入锥尖参数变化规律。进而基于CPT测试p–y模型研究了基坑开挖卸荷前后邻近既有单桩的水平承载力损失及桩身弯矩分布特征。分别考察了基坑开挖卸荷后邻近桩基试桩加载模式下的残余水平承载力和桩顶加载联合土体位移共同作用下的卸荷桩基水平承载特性。研究表明,依据真实卸荷土体CPT参数更能准确预测桩基水平承载力损失程度及损失特征,卸荷桩设计阶段须同时考虑卸荷桩较自由场地桩基的水平承载力损失及土体运动位移对桩基水平承载的影响。以上研究为合理确定基坑开挖引起的既有桩基水平承载力损失提供了一种技术思路,同时对卸荷桩水平承载性能评价具有参考意义。

Prediction of lateral capacity losses of a single pile adjacent to excavation of foundation pits based on CPT tests

The prediction of lateral capacity losses of a single pile adjacent to the excavation of foundation pits is made, by designing the excavation of a test pit in multi-layer soils based on CPT tests. The CPT-q_c curves before and after the excavation of the test pit are obtained and compared, and the lateral capacity losses of the single pile adjacent to the excavation of the test pit and its bending moment characteristics are analyzed using CPT-based p-y curve models. The residual lateral capacity of the test pile after exaction unloading and the lateral bearing rules facing the combined loadings from horizontal forces on pile head and soil movement forces are evaluated. The results show that using the actual CPT parameters of unloading soils is more reasonable than that of free-ground soils for the prediction of lateral capacity losses of a single pile adjacent to the excavation of foundation pits. The lateral capacity reduction after adjacent excavation unloading and the influences of lateral soil movement on piles must be taken into account in the design of engineering pile foundations. The study about CPT tests on unloading soils gives a technical approach for estimating the lateral capacity losses of the single pile adjacent to the excavation of foundation pits and has referential meanings for the evaluation of excavation unloading piles.