颗粒形状对砂土抗剪强度及桩端阻力影响机制试验研究  

EXPERIMENTAL STUDY OF EFFECT OF PARTICLE SHAPES ON SHEAR STRENGTH OF SAND AND TIP RESISTANCE OF DRIVEN PILES

作　　者：刘清秉[1] 项伟[1] B.M.LEHANE 崔德山[1] 李雨浓[3] 

机构地区：[1]中国地质大学工程学院,湖北武汉430074 [2]西澳大学土木工程与资源学院 [3]同济大学地下建筑与工程系,上海200092

出　　处：《岩石力学与工程学报》2011年第2期400-410,共11页Chinese Journal of Rock Mechanics and Engineering

基　　金："十一五"国家科技支撑计划项目(2008BAC47B02)

摘　　要：为研究颗粒形状对砂土的力学及变形性质的影响,以3种不同颗粒形状的均粒砂及相似材料"玻璃球"为研究对象,通过光学显微镜获取颗粒数字图像,借助图形处理系统获取颗粒单元体几何参数,定义构建2种不同层次的形状描述指标(球形度、磨圆度),并通过计算机辅助程序完成颗粒形状参数的量化。通过4种颗粒材料直剪试验,获得临界摩擦角、剪胀角及峰值摩擦角等强度指标,并分析其随颗粒形状参数的变化,通过饱和试样在不同密实度、不同离心加速度下的静力触探测试来模拟不同砂土地基上的中等圆形闭口桩静压贯入过程,并探讨桩端阻力随颗粒形状的变化关系。直剪试验结果表明:在矿物组分相同的情况下,砂土临界摩擦角随颗粒的磨圆度和规则性的增加呈线性减小,剪胀性随颗粒的不规则性的增大而增大,并可通过修正的Bolton公式来量化表述形状系数对于峰值摩擦角的作用。离心试验结果表明:静力触探锥端阻力可直接用于桩端阻力(qb)的估算,具有很好的可信度,砂颗粒形状越偏离标准球状,表面棱角度越突出,桩贯入所受阻力越大,桩端承载力越高。通过理论分析,提出一种迭代计算方法,并量化分析桩端阻力(qb)、相对密度(Dr)、应力水平(σv′)和颗粒形状(ρ)四者的相互作用关系,该方法计算结果与试验实测数据具有良好的吻合度。To study the effect of particle shape on mechanical and deformation properties of sand,three kinds of sands with different particle shapes and similar materials that are glass beads are selected. A light microscope is employed to capture the particle digital images,which are then processed to obtain the geometric parameters of particles. Two shape parameters,sphericity and roundness,are defined and quantified using the plug-in JAVA language. A series of direct shear and centrifugal cone penetration tests（CPTs） are conducted to examine the relative effect of particle shapes on the shearing friction angle and pile tip resistance. The direct shear test results show that the critical friction angle reduces linearly with the increase in roundness and particle regularity,while the dilation angle increases with the increase in particle irregularity. A modified equation can be employed to describe the relative effect of particle shapes on the peak friction angle. The centrifugal tests indicate the CPTs can be highly relied upon in the case of predicting the pile tip resistance. The sand that has a more irregular shape,i.e. deviation from sphericity and more angular,can exert a higher pile tip resistance. Moreover,an iterative method is proposed to quantify the interaction of pile tip resistance,relative density,stress level and particle shape;and the predicted tip resistance derived from this method agrees well with the measured one.

关 键 词：土力学 砂土 颗粒形状 剪切摩擦角 离心静力触探试验 桩端阻力 

分 类 号：TU43[建筑科学—岩土工程]