沉箱-垫层-桩复合基础竖向特性的细观试验  

Meso-experiment on Vertical Characteristics of Caisson-cushion-pile Composite Foundation

作　　者：朱小军[1,2] 费康[2] 李文帅[2] 许朝阳[2] 龚维明[1] 

机构地区：[1]东南大学土木工程学院,江苏南京210096 [2]扬州大学建筑科学与工程学院,江苏扬州225127

出　　处：《中国公路学报》2017年第10期93-99,共7页China Journal of Highway and Transport

基　　金：江苏省自然科学基金项目(BK20141279;BK20170509);江苏省高校自然科学基金项目(15KJB580013)

摘　　要：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 investigate the vertical bearing characteristics of caisson-cushion-pile composite foundation,a vertical bearing capacity test in view of piled-caisson of deep-water bridge test model was conducted in allusion to three different particle size distributions of gravel cushions. The side friction of pile,pile penetration,gravel flow trend and cushion porosity were developed by applying vertical loads on caisson,embedding strain gauges, soil pressure cells and displacement meter on the pile shaft.Continuous shooting with particle image velocimetry technique was provided during the test. And soil particle displacement field was obtained by dint of the image processing technique. The particle flow code（ PFC^2D） was employed to analyze the meso-characteristics such as stress transfer mode and porosity of composite foundation. The results show that the gravel particle size distribution has a great influence on the pile penetration. The pile penetration can be reduced effectively by the coarse and graded gravel. The neutral plane of the pile shaft is probably at a depth of 0. 4 times pile length and then moved downwardsto a depth of 0. 7 times pile length. Meanwhile,the porosity of pile head area decreases from 29. 2% to11. 2%. The obvious decline indicates that the particles in pile head area are compacted and formed into a core area. And it is consistent with the soil displacement field obtained by the digital image processing.The result of laboratory simulation is consistent with the numerical results from PFC^2D. The porosity of the caisson corner edge tends to decrease at first and then increase. The dilatancy characteristics of soil are revealed. The porosity of pile top soil continues to decrease,forming the pile core compaction zone. The research results can provide references for the design of pile-caisson foundation of deep-water bridge.

关 键 词：桥梁工程 竖向特性 细观试验 桩箱基础 颗粒流 

分 类 号：U445.557[建筑科学—桥梁与隧道工程]