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Simulating the PCC pile composite foundation for centrifuge modelling and pile-soil interaction
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摘要: 针对现有刚性桩复合地基离心模型试验技术的诸多局限性，综合考虑模型在材料、几何及桩土接触上的相似，首次设计了PCC桩复合地基离心模型试验并探讨了模型制备方法。配合专用切削、取土及回填试验器材，可以整齐高效地实现削土刮平、引孔取土、压桩就位和桩内回填操作，将常重力场下模型制备引起的扰动最小化，优化PCC桩复合地基离心模型制作过程。设计并开展反映本次离心模型中桩土摩擦接触特性的直剪试验，结果表明，离心模型中的桩帽与路堤砂、粗糙化的模型桩与软土层及下卧层的接触面摩尔-库伦摩擦角取值均在合理范围内，能够较好地代表PCC桩的桩-土接触特性。Abstract: The centrifuge modelling of PCC pile composite foundation is designed for the first time to consider the similarity of material, geometry and pile-soil interaction. The model preparation method which can eliminate many limitations of the existing centrifugal modelling technology of rigid pile composite foundation is well proposed. With special cutting, extraction and backfilling equipment, the operation of soil scraping and extraction, pile driving and backfilling can be realized neatly and efficiently. Therefore, the model preparation disturbance in 1g field can be minimized, and the centrifugal modelling of PCC pile composite foundation is well optimized. The values of Mohr-Coulomb interface friction angle of pile cap versus embankment sand, roughened model pile versus soft soil, and roughened model pile versus underlying soil derived from the direct shear test results are all within a reasonable range, and can reflect the pile-soil contact characteristics of cast-in-situ concrete piles in a reasonable way.
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图 1 路堤下PCC桩复合地基离心模型
Figure 1. Centrifugal model of PCC pile composite foundation under embankment
图 4 桩土接触面直剪试验器材
Figure 4. Equipment and materials for pile-soil interface direct shear test
图 6 最大剪应力与法向应力线性关系
Figure 6. Linear relationship between maximum shear stress and normal stress
表 1 离心模型试验土样参数
Table 1. Soil sample parameters in centrifugal model test
土样 液限/% 塑限/% 目标强度/kPa 目标密度/（g·cm−3） 原型厚度/m 模型厚度/mm 土性 路堤砂 / / / 1.97 6.0 100 粉细砂+铁矿粉 软土层(饱和) 41 20 20 1.90 9.6 160 黏土 下卧层(饱和) 29 16 40 2.00 9.0 150 粉质黏土 
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表 2 接触面直剪试验参数
Table 2. Direct shear test parameters of pile-soil interface
土层 初始含水率/% 上覆荷载/kPa 剪切速率/(mm·min−1) 剪切位移/mm 摩擦系数 摩擦角/° 有效内摩擦角/° δ/φ' 路堤砂 3 50,100,150,200 1.0 30 0.64 33 41 0.80 软土 31 40,70,100,130 0.5 10 0.46 25 29 0.86 下卧层 23 40,80,120,160 0.5 10 0.58 30 33 0.91
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