Abstract: It is easy to observe the development of vertical joints of aeolian loess on the edge or shore of a plateau, and these vertical joints can readily induce loess disasters due to changes in the water environment. The vertical joints of loess were investigated in this study. The developmental laws of vertical joints of loess in horizontal and vertical directions were summarized based on their meso-microscopic developmental characteristics. The display forms, transformation mechanisms and the micro-mesoscopic structural basis for forming vertical joints of loess were observed on different evaluation scales. Based on the sedimentary dynamics of loess, the vertical developmental mechanism of vertical joints was discussed. Studies had shown that vertical joints formed gradually during the historical sedimentary process and were the product of diagenesis. It was proposed that the pore concentration zone and vertical tubular channel in loess were the micro-mesoscopic structural basis for the development of vertical joints, for which the results of a three-dimensional CT scanning test provided strong evidence. The vertical joints exhibit different forms on different evaluation scales. Under external actions (wet and dry cycling and loess pile thickening), the vertical joints in the micro-meso-sub-macro point of view can be developed in an upward scale (expansion characteristics) or downward scale (decay characteristics), and they can transform between the two scales. This is referred as the scale conversion mechanism. The vertical developmental mechanism of vertical joints of loess was also proposed based on this.

Key words: vertical joints, structural unit, scale transformation, developmental mechanism