Topplin g - - A Fundamental Failure Mode In Discontinuous Materials --- Description and analysis 1

Toppling of rock blocks, individually, or in rock masses of great volume, is now understood to be an important potential mode of failure for rock slopes. Toppling can also occur in foundations, in tunnels and underground chambers and on a small scale in any rocky landscape where frost, creep, or water forces are at play. Toppling failures can develop slowly as an expression of creep, or they can occur suddenly and powerfully. This paper describes the features of toppled rock masses in nature, and in base friction models - - distinguishing between primary and secondary toppling, and block-toppling versus flexural toppling. Some excellent structural engineering methodology has now been published for calculating the potential hazard, and the necessary strengthening of rock masses capable of forward rotation under excavation or load. These methods are described in the context of design approaches for supporting new rock excavations. Finally some important case histories relating to power and land developments in California are mentioned.