Chapter 17 - Types of Failures of Rock and Soil Slopes

Abstract

The classification of rock and soil slopes is based on the mode of failure. In the majority of cases, the slope failures in rock masses are governed by joints and occur across surfaces formed by one or several joints. Some common modes of failure, which are frequently found in the field, are described in this chapter. One of the failures discussed is planar (translational) failure; it takes place along prevalent and/or continuous joints dipping toward the slope with strike nearly parallel (±15°) to the slope face. Stability condition occurs if critical joint dip is less than the slope angle and mobilized joint shear strength is not enough to assure stability. In addition, wedge failure is also discussed, which occurs along two joints of different sets when these two discontinuities strike obliquely across the slope face and their line of intersection daylights in the slope face. The wedge failure depends on joint attitude and conditions and is more frequent than planar failure. The factor of safety of a rock wedge to slide increases significantly with the decreasing wedge angle for any given dip of the intersection of its two joint planes.