K_0条件下颗粒形状特征对砂土剪切模量的影响

Effect of particle shape on shear modulus of sand in K_0 condition

为了研究颗粒形状特征对砂土剪切模量的影响,选取4种形状不同的砂样(福建标准砂和人工石英砂)作为研究对象,通过扫描电镜获取其颗粒微观图像,使用Image Pro Plus软件和自编Matlab程序提取试样颗粒的形状特征。采用改进的半径角和轮廓指数综合描述颗粒偏离圆或椭圆的程度以及棱角变化程度,并基于这两个参数提出颗粒形状因子来综合表征颗粒的形状特征。之后在K_0条件下通过弯曲元试验获得不同竖向荷载对应的4个试样的剪切模量,试验结果表明,砂土颗粒的形状因子与砂土的剪切模量具有良好的相关性。最后基于Hertz-Mindlin接触模型,推导出引入形状因子的砂土剪切模量理论计算公式,该计算公式与实测值吻合良好。

To study the effect of particle shape on shear modulus of sand, four sand samples with different particle shapes and grain sizes are prepared, including Fujian standard sand and artificial quartz sand. Image Pro Plus and Matlab program can extract the geometric parameters of particles from images of four samples obtained by scanning electron microscope. Two geometric parameters, radius angularity and form index, are improved and studied. Through statistical data of sand particle, the results show that radius angularity and form index describe different aspects of particle shape. As such, shape factor of sand is proposed based on radius angularity and form index to generalize particle shape. Then, a series of model tests in K0 condition is conducted to obtain the shear modulus of samples under different vertical stresses by bender element deployed in the sand. The tests show that shape factor is closely related with shear modulus of sand. Finally, based on Hertz-Mindlin contact model, shape factor is introduced to derive the formula of sand＇s shear modulus, which agrees well with the measured one.