南京下蜀黄土图解法与矩值法粒度参数对比研究

Comparative study on grain-size parameters of Xiashu loess derived from graphic and moment methods in Nanjing

根据图解法和矩值法的计算原理,对南京江北地区下蜀黄土58个样品分别进行定量计算,并对两种方法所得结果进行对比研究.结果表明,两种计算结果的平均粒径具有高度相关性,相关方程为y=0.790 3x+1.512 3,决定系数为0.952 5,计算得到相关系数为0.976 0,表明两种方法得到的平均粒径基本相等,可以互相代替;标准偏差相关方程为y=0.906 2x+0.109 6,决定系数为0.971 2,相关系数为0.985.而偏态和峰态较为离散,不具有相关性.造成这两种结果差异的主要原因在于计算原理不同.图解法统计样品的90%子样,矩值法统计样品粒度分布的总体特征.偏态注重粒度分布的尾部,峰态关注峰的宽窄,且由于古土壤呈明显的双峰分布,因而高阶偏态和峰态差异显著.通过对比研究发现,矩值法计算的粒度参数对下蜀黄土研究具有更高的精确性和可靠性.

In terms of calculation principle of graphic method and moment method, grain-size parameters of fifty-eight samples of Xiashu loess on the north bank of Yangtze River are calculated respectively, then a contrast of these two methods is made. The results indicate that the mean grainsize values derived from two methods are correlated significantly. Their relationship can be described with the equation of y = 0.790 3x ＋ 1.512 3, the determining coefficient is 0. 952 5, and the correlation coefficient is 0. 976 0, which indicates that the mean grain-size values derived from two methods are equal basically and one could replace the other, The correlation equation of standard deviation is y = 0. 906 2x ＋ 0. 109 6, the determining coefficient is 0. 971 2, the correlation coefficient is 0. 985 0, and the skewness and kurtosis are discrete and not correlated. The main reason of two different results is the different calculating principles. Graphic method reflects the characteristics of 90 percent of samples, while moment method considers the whole characteristic of grain-size distribution. The skewness is particularly on the tail of grain size distribution, and the kurtosis is particularly on the width of the apex. Because of the characteristic of paleosol＇s distribution of double-apices, the differences between high-order skewness and kurtosis are obvious. By comparative study, it is found that grain-size parameters derived from moment method is more accurate and reliable to the research on xiashu loess.