Experimental study of the bearing capacity of a drainage pipe pile under vacuum consolidation

Abstract

In this study, we propose a drainage pipe pile under vacuum consolidation to integrate foundation treatment and pile foundation engineering in soft soil areas. To study its bearing capacity characteristics and foundation treatment performance, single pile static load tests, vane shear tests, and water content tests were carried out for ordinary piles, perforated piles, and drainage pipe piles under conditions of static and vacuum consolidation. Based on the results, the concept of strong and weak reinforcement areas was proposed and used for bearing capacity prediction. The results showed that the drainage pipe pile did not become silted under vacuum consolidation. The single pile bearing capacity was much higher than that of an ordinary pile, and the pile side friction was exerted mainly in the middle and lower parts. Good results were achieved using the shear strength at the junction of the strong and weak reinforcement areas to estimate the ultimate bearing capacity of a single pile. This study provided important insights into the design and construction of drainage pipe piles in a soft soil foundation.

摘要

目的

为进一步促进地基处理与桩基工程的结合, 本文提出真空固结排水管桩。通过与普通桩与开孔桩对比, 研究真空固结排水管桩的承载力增长趋势、桩侧摩阻力分布、桩周土抗剪强度与含水量的变化规律等, 为真空固结排水管桩应用与实际工程提供理论依据。

创新点

1. 提出了一种能加快软土固结且不会发生淤堵的地基处理与桩基工程相结合的真空固结排水管桩; 2. 通过承载力、含水量、十字板剪切等试验定义了真空固结排水管桩对桩周土的强(弱)增强区, 并利用该定义修正规范, 提出了一种单桩极限承载力估算方法。

方法

1. 对静压和真空预压条件下的管桩、钻孔桩和排水管桩进行单桩静载试验、十字板剪切试验和含水量试验; 2. 根据试验结果, 对比分析不同桩型在不同工况下单桩承载力、桩身轴力和桩侧摩阻力的变化规律(图7∼9); 3. 对桩周土体不同位置的抗剪强度和含水量分布进行试验(图11∼15)。

结论

1. 真空固结排水管桩无淤塞现象; 根据单桩静载试验, 真空固结排水管桩承载力从普通管桩的89.5 N提高到271.5 N, 提升约3倍(考虑到桩顶密封对真空度的影响以及桩间距对排水固结的影响, 实际工程中增长幅度可能会下降); 一方面, 孔隙水在负压作用下加速排泄, 提高了土体的抗剪强度; 另一方面, 土壤中的细颗粒逐渐聚集到桩壁上, 形成一个密实的土层, 从而扩大桩径。2. 真空固结排水管桩最大桩摩阻力是普通桩的3∼4倍, 且真空固结改变了摩擦阻力的分布形式; 桩侧摩阻力在桩的中下部得到了更好的发挥。3. 加固区半径与排水量呈正相关; 利用两个区域交界处的抗剪强度来估算单桩的极限承载力可以取得良好的效果。