**6.4.1
Two-dimensional analysis versus three-dimensional analysis**

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The slope can be simulated in 2D or 3D by numerical modeling (figure 10 & 11). It depends on many factors such as time require for simulation, critical parameter, requirement of simulation, field condition and computer configuration. Most design analyses for slopes assume a two- dimensional geometry comprising a unit slice through an infinitely long slope under plane strain conditions, i.e. the radius of both the toe and the crest are assumed to be infinite. However, three-dimensional analyses are required when the direction of major geological discontinuities does not strike within 20–30◦ of the strike of the slope or the distribution of geomechanical units varies along the strike of the slope. This also becomes necessary when the slope geometry in plan cannot be represented by two-dimensional analysis, which assumes axisymmetric or plain strain condition.

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Figure 10: 3D Simulation by Ansys software based on Finite element method

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Figure 11: 2D Simulation by Geoslope software based on Finite element method

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