In Mining Engineering, a stable arch formed across a pit provides benefit in design of undercut slope; therefore, prediction of the maximum undercut width which does not cause collapse is needed. This study extends a basic idealization of stationary system used by Jenike (1961) to the stability of laterally confined rigid block inclining on a stiff bedding plane. Similar assumptions on resistance supporting the arch is characterized by unconfined compressive strength and load breaking the arch is due to its own weight and force exerted by the material above the arch were adopted in the present study with an additional consideration of interface resistance.Moreover, a series of simple experiments using a block of compacted moist sand confined by parallel rigid walls were conducted with variation of thickness, width and length. The inclined angle of bedding plane was gradually increased until the block starts to slip. The relationship between a stable width and an inclined angle was obtained experimentally to confirm the developed theoretical relationship. For design purpose of undercut mining, this particular relationship provides a lower bound for the maximum span where load could laterally transferred to vertical planes of neighboring rock mass.

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