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6.0 Introduction **

Numerical models are mathematical models that use some sort
of numerical time-stepping procedure to obtain the models behavior over time.
These are computer programs that represent the mechanical response of a rock
mass subjected to a set of initial conditions such as *in situ *stresses
and water levels, boundary conditions and induced changes such as slope
excavation. Numerical models divide the rock mass into zones. Each zone is
assigned a material model and properties. The result of a numerical model can be
extrapolated confidently outside its database in comparison to empirical methods
in which the failure mode is explicitly defined. It can also incorporate
geologic features such as faults and ground water, providing more realistic
approximations of behavior of real slopes than analytical models.

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Numerical modelling techniques have been widely used to solve complex slope problems, which otherwise, could not have been possible using conventional techniques. These models are used to simulate rock slope as well soil slope with complex conditions. All rock slopes involve many discontinuities such as joint, fault, bedding plane, etc. Precise representation of discontinuities in numerical models depends on the type of model.

Numerical methods of analysis used for rock slope stability investigations may be divided into three approaches:

- Continuum modeling
- Discontinuum modeling
- Hybrid modeling