Influence of the dust source distance on the multimodal grain-size distribution characteristics of loess

Abstract：By using high-resolution laser grain-size instrument Mastersizer 2000, the authors performed a systematic study of the grain-size distribution characteristics of loess samples from Weinan in Shanxi province, Linshan in Beijing and Mangshan in Henan province, summed up the differences in multimodal grain-size distribution among three types of loess and discussed the influence of the dust source distance on the multimodal grain-size distribution characteristics of loess. The main conclusions are as follows： (1) Suspended particles with a diameter of <70 μm are dominant. There are three fractions for grain size distribution of loess： fine, mediun and coarse (the median sizes are <1 μm, 1-10 μm and 10-70 μm, respectively). The coarse fraction, which has the highest percentage, has the most distinct peak. The grain sizes and percentages of the coarse and medium fractions are controlled by the source distance. (2) The grain sizes of loess dust in different areas are notably different. The median grain size of the coarse fraction decreases with increasing source distance, showing a negative correlation; whereas the percentage of the medium fraction increases with increasing source distance, showing a positive correlation. (3) The separation of grain size fractions can reflect the minute difference in grain size in the same source region and has advantages. (4) The relation between the median size of the coarse fraction of loess and the dust source distance may be deduced theoretically and its correctness may be checked and validated by the actual fitting function.