Selecting a suitable mechanical model to represent the behavior of Hard Soils-Soft Rocks (HSSR) is a challenge for mining engineers. HSSR has intermediate properties between those of soils and hard rocks, it has a Uniaxial compressive strength (UCS) in the range 0.25 Mpa - 25 Mpa. Different constitutive models were proposed to represent the behavior of HSSR with a lack of certainty of their results. The applied mechanical models may be simple with few required input parameters or sophisticated with more input parameters. Using a simple model is easier than sophisticated one, but with lower accuracy. A compromise should be made. Two different mechanical models are used to study the effect of the mechanical model and the applicability of using more complex mechanical model. Mohr-Coulomb (M-C) as an example of simple models and Double Yield (DY) as a more complex one with multiple yield surfaces. The results show that the stresses around a circular opening excavated into a HSSR material begin to alter when using the more complex model at certain depth. At any depth smaller than this, there is no significant difference. This is related to the value of the resulting vertical stresses compared to the value of pre-consolidation pressure of the ground. Also, the DY model predicts higher safety factor. This sets a condition where using a more complex model is required.

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