考虑断裂破坏的水泥土桩原位旁压强度检测方法

    Technology of mass detection of cement mixing pile based on pressuremeter tests

    • 摘要: 现有水泥土桩质量检测常规方法存在桩体薄弱点样本缺失、样本扰动失真、钻孔取芯作业难度大成本高等问题。针对以上问题,首先开展水泥土桩足尺模型试验揭示桩体内旁压试验过程贯穿断裂破坏规律;接着基于贯穿断裂破坏模型和桩体的有界性提出水泥土单轴抗压强度与桩体内旁压临塑压力、初始压力的关系模型;最后开展现场试验进行水泥土桩旁压试验与取芯试验,对比抗压强度的预测值和实测值。研究结果表明;旁压试验条件下桩体的破坏裂缝为单一的径向贯穿拉裂面,在桩体直径上大致呈对称状;水泥土的破坏极具脆性,旁压P-S曲线不具有塑性阶段,临塑压力最大值处于桩体中部粉砂层,而最小值处于淤泥层。采用的旁压试验检测方法和考虑贯穿断裂破环的强度换算公式可以合理预测水泥土桩抗压强度。

       

      Abstract: The existing conventional methods for quality testing of cement mixing piles face challenges such as missing samples at weak points of the pile, sample distortion due to disturbance, and the high difficulty and cost of drilling and coring operations. To address these issues, first a full-scale model test on a cement mixing pile is conducted to reveal the through-going fracture failure pattern during lateral pressure inside the pile. Based on this fracture failure model and the bounded nature of the pile, a model is then proposed to relate the uniaxial compressive strength of the cement soil to the limit the plastic pressure and the initial pressure under lateral compression conditions. Finally, a field test is carried out, in which the lateral pressure testing and coring are performed on the cement mixing pile, and the predicted compressive strength is compared with the actual measurements. The results show that, under lateral pressure, the pile fails along a single radial through-going tensile fracture plane that is roughly symmetric along the pile diameter. The cement soil fails in a highly brittle manner, and the P-S curve obtained from the lateral pressure tests does not exhibit a plastic stage. The maximum limit plastic pressure is observed in the silt layer at the mid-height of the pile, while the minimum value occurs in the sludge layer. The lateral pressure testing method used in this study, along with the strength conversion formula that accounts for through-going fracture failure, can reliably predict the compressive strength of cement mixing piles.

       

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