不同前处理方法对下蜀黄土粒度测量的影响

采用7种前处理方法对南京泰山新村下蜀黄土剖面30个样品进行了粒度分析，以探讨不同前处理方法对下蜀黄土粒度测量结果的影响。结果表明：（1）方法A（未做任何前处理）和方法D（加盐酸处理）的粒度频率分布曲线都呈单峰分布特征，而其他5种前处理方法处理后的粒度频率分布曲线都呈双峰分布特征，而且在双峰曲线的细粒端还存在一个很小的超细粒组分。（2）下蜀黄土中含有一定含量的有机质，尤其是古土壤层中的有机质含量更高，会明显影响粒度测量的结果。因而，下蜀黄土在进行粒度测量前处理时，需要加双氧水去除有机质。（3）下蜀黄土因处于湿热环境，淋溶作用强烈，碳酸盐含量极低，因而粒度测量时无需加盐酸去除碳酸盐。盐酸可能会与矿物发生反应，过剩的盐酸使溶液呈现较强的酸性促使土壤颗粒凝聚，使得所测粒径偏粗，而且使μm的超细粒组分含量减少。因此，综合理论和经验分析，推荐了一种较好的进行下蜀黄土粒度测量的前处理方法G，即先使用双氧水去除有机质，静置一夜，再使用（NaPO3）6分散剂，然后用超声波清洗机振荡后上机测试。

INFLUENCE OF PRETREATMENT METHODS ON GRAIN-SIZE DISTRIBUTION PATTERN OF THE XIASHU LOESS

7 methods were adopted to pretreat the 30 Xiashu Loess samples from the Taishan Village at Nanjing to check the bias of different methods on grain-size distribution pattern. Our results indicate that:(1) Grain size frequency curves using Method A (without any pretreating) and method D (pretreated with hydrochloric acid) are all unimodal in distribution pattern, but the frequency curves using other five methods are bimodal. There is a small proportion of very fine grains in the fine grain fraction of the bimodal curve. The Xiashu Loess contains certain amount of organic matter, especially in the paleosol layers, which has significant influence on grain size distribution. It is a necessity to remove the organic matter before grain size analysis to be carried out. Owing to the hot and humid climate and strong leaching, carbonate content is relatively low in the Xiashu Loess, so it is not necessary to remove carbonate before grain size analysis. Moreover, hydrochloric acid may react with some minerals, and the excessive hydrochloric acid shall make the solution more acid, leading to flocculation of soil particles, that will make the grain size coarser, and deducing of the very fine component. In this regard, it is recommended that the method of G be used for pretreatment of the Xiashu Loess samples. At First, H2O2 is used for one night to remove the organic matter, and then add(NaPO3)6 as a dispersant to disintegrate the sample, and finally ultrasonic cleaning instrument is recommended before grain size analysis to be proceeded.