1 EVOLUTION OF SHEAR STRENGTH OF CLAYEY SOILS IN A LANDSLIDE DUE TO ACID RAIN: A CASE STUDY IN THE AREA OF THREE GORGES, CHINA

Abstract: Possible effects on landslide inception by acid rain induced changes in soil strength are investigated. Soil samples from freshly exposed slip surfaces and their immediate vicinity have been investigated at two landslides in the region of the Three Gorges, China. A visibly higher smectite content at the slip-surface and a dominant content of illite in the immediate vicinity are observed. In laboratory, remolded soils were subjected to acid water bath and tested for changes in their mineralogical composition and in their shear strength after the bath of different duration. The largest changes occur in the internal friction angle, which drops over one-third, concomitant with alteration of the originally smectitic soil with a substantial illite component into completely smectite dominated soil. Subsequently the friction rises again, simultaneously with neoformation of kaolinite at the expense of the smectite component. Changes in cohesion are much less significant. The originally koalinite-rich and illite-rich samples were found to be much more stable. A chemo-mechanical model of clayey soils is discussed