Planar failure -> case of rock mass sliding on a single surface (special case of general wedge type of failure) two-dimensional analysis may be used according to the concept of a block resisting on an inclined plane at limit equilibrium.

Rock slope stability analysis based on limit equilibrium techniques may consider following modes of failures: The inclinations of the slice interfaces are varied until a critical criterion is met. The shear strength criterion is applied to the shears on the sides and bottom of each slice. The direction of the resultant interslice force is equal to the average of the ground surface and the slope of the base of each slice. The resultant interslice force is either parallel to the ground surface or equal to the average slope from the beginning to the end of the slip surface.

The fractions of the function value needed for force and moment balance is computed.

The direction of the resultant interslice forces is defined using an arbitrary function. Same as Spencer's method but with a constant acceleration force on each slice. The resultant interslice forces have constant slope throughout the sliding mass. An empirical correction factor is used to account for interslice shear forces.Īn assumed line of thrust is used to define the location of the interslice normal force. Resultant interslice forces are horizontal. The assumptions made by a number of limit equilibrium methods are listed in the table below. Risk assessment is concerned with both the consequence of slope failure and the probability of failure (both require an understanding of the failure mechanism). In addition, the use of the risk assessment concept is increasing today. Also, even for very simple slopes, the results obtained with typical limit equilibrium methods currently in use (Bishop, Spencer, etc.) may differ considerably. In these cases more sophisticated numerical modelling techniques should be utilised. internal deformation and brittle fracture, progressive creep, liquefaction of weaker soil layers, etc.). For example, limit equilibrium is most commonly used and simple solution method, but it can become inadequate if the slope fails by complex mechanisms (e.g. The engineer must fully understand limitations of each technique. Finite element limit analysis, Discontinuity layout optimization) to complex and sophisticated numerical solutions (finite-/distinct-element codes). Today engineers have a lot of possibilities to use analysis software, ranges from simple limit equilibrium techniques through to computational limit analysis approaches (e.g. Before the computer age stability analysis was performed graphically or by using a hand-held calculator.

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