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为了分析沉箱-垫层-桩复合基础的竖向受力特性,以深水桥梁桩箱基础试验模型为背景,针对3组不同级配砂石垫层,进行了桩箱基础竖向承载特性试验。通过在沉箱顶部施加竖向荷载、桩身埋设应变片、土压力计以及位移计等测试方法,并在试验过程中采用粒子图像测速(PIV)技术进行连续跟踪拍摄,得到桩身侧摩阻力、桩顶刺入量、砂石流动趋势及垫层孔隙率等变化规律,利用图像处理技术获取了土体颗粒位移场,并采用颗粒流程序PFC~(2D)对该复合基础应力传递方式和孔隙率等细观特性进行补充分析。研究结果表明:砂石垫层颗粒级配对桩顶刺入量有较大影响,由粗集料和良好级配骨料砂石构成的垫层可有效减小桩顶刺入量;沉箱下沉时,桩身中性点位置从0.4L处下移到0.7L处,同时桩顶区域孔隙率由29.2%降低至11.2%,下降幅度较为明显,表明其颗粒被挤压密实形成核心区,与数字图像处理得出的土体位移场形态相吻合;PFC~(2D)程序分析结果与室内模拟的规律较为一致,沉箱刃脚处土体孔隙率经历了先下降后升高的过程,表现出土体的剪胀特性,而桩顶处土体孔隙率值持续降低,形成桩顶核心压密区。研究成果可为深水桥梁桩箱基础设计提供参考。
In order to analyze the vertical force characteristics of caisson-cushion-pile composite foundation, the vertical bearing behavior of pile foundation is tested on the basis of the foundation test model of deep-water bridge pile-box foundation. By applying vertical load on the top of caissons, buried strain gauges, earth pressure gauges and displacement meters and other test methods, and using particle image velocimetry (PIV) during the test to track continuously to get the pile body side frictional resistance, The penetration of pile tip, the trend of sandstone flow and the porosity of bedding were studied. The displacement field of soil particles was obtained by using image processing technology. The particle flow program PFC 2D was used to calculate the stress distribution and pore- Rate and other meso-characteristics for additional analysis. The results show that the particle grading of sandstone cushion has a significant influence on the amount of penetration of the top of the pile, and the cushion composed of coarse aggregate and fine graded aggregate sand can effectively reduce the penetration of pile top. , The position of the neutral point of the pile moved downward from 0.4L to 0.7L, and the porosity in the top of the pile decreased from 29.2% to 11.2%, which was obviously decreased, indicating that the pellets were squeezed to form the core zone closely with The result of PFC ~ (2D) program is consistent with the law of indoor simulation. The porosity of soil at the caisson edge undergoes the process of first decreasing and then increasing, showing that soil Body dilatancy characteristics, while the top of the pile at the soil porosity continued to reduce the value of the formation of the top of the pile core pressure zone. The research results can provide references for the foundation design of deepwater bridge pile box.