Degree of adversity of discontinuity orientation in relation to rock slope instability

This research aims to investigate strength anisotropy and how it mobilises in rock masses associated with slope failure by performing limit equilibrium and finite element method analysis on selected landslides, and to establish a revised rock mass classification which relates the mechanical behaviour of rock masses that take more account of structural geology input.

The Hoek Brown Failure Criterion suggests that rock mass strength is dependent primarily on lithological type, fracture spacing and intact rock strength relative to the ins-situ stress level. A fundamental assumption of the criterion is that the rock mass to which it is applied is homogeneous and isotropic. Therefore, the criterion makes no allowance for the degree of diversity of discontinuity orientation within the highly fractured rock mass. Thus, the hypothesis to be tested is: ‘Does the Hoek Brown Failure Criterion adequately characterise the strength of slope in anisotropic rock masses?’

It is in this type of situation that modelling plays a key role. The limit equilibrium (LEM) and finite element method (FEM) of analysis will be combined with the geological investigation, using field and laboratory measures in order to enable modelling and to analyse the rock mass as a discontinuum medium thus creating a clear understanding of the rock slopes behaviour. Seven test sites have been selected which include Mam Tor, Alport Castles, Tessina, Ruinon, La Clapiere, Randa and Pos Selim landslides.

The final result of this research would assist engineers and engineering geologists to have a better understanding in selecting reliable estimates of the strength and deformation characteristics of rock masses in the analysis for the design of slopes. Evidently, safe and economical slope design and excavation could be achieved, and highly jointed rock slopes behaviour can be anticipated. This work has been supported by a number of Engineering Geology MSc projects.