3.3 Effect of moisture condition on shear strength

The effect of moisture on shear strength of soils is very important in considering slope stability. Kjaernsli and Sande (1963) showed that the shear strength of dry soil samples is higher than that of saturated and submerged samples. However, it also depends on the type of soil or material and its partial side distribution. 

Horn and Deere (1962) observed that increases of surface moisture causes the coefficient of friction to increase for massive-structured minerals such as quartz as compared to a decrease for minerals having layer-lattice structures such as mica. He found that sliding friction on different minerals under similar testing conditions show different coefficients of friction, but minerals of the same type from different origins had the same frictional characteristics.