**6.4.1
Selecting appropriate zone size **

The next step in the process is to select an appropriate zone size. The finite difference zones assume that the stresses and strains within each zone do not differ with position within the zone. It is necessary to use relatively fine discretizations in order to capture stress and strain gradients within the slope adequately. Finite element programs using higher-order elements require less zones than the constant strain/constant stress elements common in finite difference codes. As shown in figure 14 the coarse model(a) yields a very crude approximation of the factor of safety. A properly descritized model as shown in figure 14(b) provides a fair estimate of the safety factor without compromise is solution accuracy and time as compared to an intensively descritized model (c).

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Figure 14: Shows the different view discritized view
of internal dump slope**

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