The stress state on two slope profiles overlying an inclined surface with layer inclination of 5° and 15° are investigated. It is demonstrated that the induced stress state in an imbedded weak layer, exposed at the base of the slope, forms a zone of induced tensile vertical and horizontal stresses, which can lead to failure. The zone length depends on the slope angle and the angle of the inclined layers.
L'etat des contraintes sur deux profils en pente en superposition sur une surface inclinee avec une inclinaison de couche de 5o et 15o est etudie. L'etude presente demontre que l'etat induit des contraintes dans une couche faible inseree, exposee au bas de la pente, forme une zone de contraintes de traction induites horizontales et verticales, qui peut amener à la rupture. La longueur de la zone depend de l'angle de la pente et l'angle des couches inclinees.
Die Druckvorkommnisse zweier Hangprofile auf einer schragen Flache mit einer Schichtneigung von 5° und 15° wurden untersucht. Es zeigte sich, dass die induzierten Druckvorkommnisse in einer eingebetteten schwachen Schicht, die am Hangfuße offen liegt, einen Guertel induzierter vertikaler und horizontaler Zugkrafte bildet, die zum Zusammenbruch fuehren können. Die Guertellange ist von der Neigung des Hanges und der Neigung der schragen Schichten abhangig.
Sturman (1984), Stead and Scoble (1986), Singh, T.N and Singh, D.P (1992) and Boyd (1983) reported different cases on slope instabilities. In their analyses the landslide event didn't coincide with the standard failure mechanisms. In these cases, clearly could be recognized two block types (so called "passive" and "active" block), which formed the failure. The experience, which the author has with the sloughs, took place in high- or lowwalls at the South African coalfields also exhibit the same behaviour at the vicinity of an angulated ground surfaces. These failures showed that the most common effect of faulting was the provision of a rear release plane, frequently with associated adverse dipping strata (not more than 15°). In almost all of the cases, the relatively weaker layer type was presented at the toe of a slope profile (for South African conditions it is shale layer imbedded in a sandstone massive). For this reason, stress state at the bottom contact plane between imbedded shale layer and sandstone massive has been investigated using final difference code FLAC2D.
Elasto-plastic analysis of geotechnical problems using the final difference (FD) method has been widely accepted in the research field for many years. Unfortunately, its regular use in geotechnical practice for stress analysis and their influence to the slope stability still remains limited. The reason for this lack of acceptance is not entirely clear; however, practicing engineers are often skeptical of the need for such complexity, especially in view of the poor quality of soil property data often available from routine site investigations. Although this skepticism is often warranted, there are certain types of geotechnical problem for which the FD approach offers real benefits.
