土体颗分曲线测试的密度计法取样量的影响分析

Study on different sampling methods for measuring particle size distribution curve by densitometry

为探究不同土取样量对颗分曲线绘制精度的影响机制,利用两种不同取样量的砂土和黏土试样进行颗分试验,并绘制对应的颗分曲线,计算出对应土样的不均匀系数C u和曲率系数C c进行对比。针对土取样量不同导致颗分曲线误差大的缺点,提出取样量改进方案,并与原曲线进行比较。最后利用考虑颗粒数量以及形状系数颗粒沉降计算公式修正国家标准所作出的颗分曲线与上述曲线进行对比。试验结果表明:1)土取样量越大颗分曲线越往上偏移且偏差量越小,且对砂土影响更大。2)在20 g及以下取样量下C c;C u值明显偏低。3)采用改进方案比原有国标方法绘制的颗分曲线精度高。其物理机制初步认定为悬浮液浓度不同导致的土颗粒沉降群体行为的浓度效应。

In order to explore the influence mechanism of different soil sampling quantity about the accuracy of the grain analysis curves,two different sampling quantity between sand and clay samples are used to carry out the particle analysis test,the corresponding particle size analysis curves are drawn,and then the corresponding soil sample’s coefficient of nonuniformity()and coefficient of curvatureare()are calculated.The shortcomings of the sample quantity improvement scheme are proposed,and the score curve made above is compared with the original curve.The particle shape coefficient,momentum equation,etc.are introduced to obtain a new particle settlement calculation formula,and the particle analysis curves made by the national standard are corrected by this way.The particle sampling curves with the soil sampling quantity method have large errors.Finally,the particle distribution curves made by the national standard are compared with the curves by using the particle sedimentation calculation formula considering the particle number and the shape factor.The test results show that:1)The more the sample quantity is,the more the upper part of the curves shift upwards,and then the deviation is smaller,and the impact on the sand soil is greater.2)The Cc and Cu are significantly lower under the sampling amount of 20 g and below.3)The curve of improved method is more accurate than the curve of original national standard method with the same plan test.The physical mechanism is identified as the aggregation(concentration)effect of the behavior of soil particle sedimentation caused by different suspension concentrations.