Abstract: To study the mechanism of clay minerals that control the softening of soft interlayers under different water contents, six types of soft interlayers in Guizhou province are collected as research objects. Direct shear tests of soft interlayers with different water content are carried out to analyze the change trend of cohesion and internal friction angle of soft interlayers with different water contents and the control effect of clay on the change trend of soft interlayers. The results show that: Montmorillonite, Illite and Chlorite contents control the variation trend of shear strength parameters of weak interlayers. (1) With the increase of water content, the cohesion and internal friction angle of the weak interlayers show a downward trend, but the change trend of different weak interlayers is different. (2) When the content of Illite in the weak interlayer accounts for more than 53% of the clay mineral content, the change trend of cohesion is similar to that of Illite; When the content of Montmorillonite exceeds the content of clay minerals by 22% and the proportion of Illite is less than 53%, it is similar to Montmorillonite. (3) When the content of Montmorillonite is more than 38% of the clay mineral content, and there is no chlorite, the change trend of internal friction angle is similar to that of Montmorillonite; When the proportion of Illite exceeds 45%, and there is no chlorite, it is similar to Illite; When Chlorite exists, and chlorite accounts for more than 26%, it is similar to chlorite. (4) In the same moisture content range, the cohesion of Montmorillonite is greater than that of Illite, and the internal friction angle of Montmorillonite is the largest, followed by Illite, and chlorite is the smallest.

Key words: Weak Interlayer, Water Content, Clay Minerals, Control Function