Application of block theory to rock slope stability studies

Application of block theory in the analysis of the complicatedly jointed abutments of Pacoima Dam, California, is demonstrated. The stability of the left abutment is evaluated using Shi’s removability theorem on mapped joint intersections which have produced block failures in the past. Joint water pressures are introduced by three dimensional parametric addition of water forces representing increasing levels of reservoir depth, and the level of water pressure necessary to cause failure is thus established. The stability analysis of the concealed right abutment is performed using the critical-key-block method (Hatzor, 1993). It is demonstrated that while the left abutment is rather unstable, the right abutment is generally safe. The major cause for the difference is shown to be the relationship between rock structure and free face orientation. The results of this study are strongly supported by the behavior of both abutments during several earthquakes of strong ground accelerations.1