Extended Ultimate-Pit-Limit Methodology for Optimizing Surface-to-Underground Mining Transition in Metal Mines

Table 1

Rock property for modifying the size of the crown pillar by the beam model.

(t·m^−3)	(kPa)		(m^−1)
4.1	77.84	3	1

Note. The beam model can be analytically described by , where H is the size of the crown pillar required to maintain the open pit and underground stopes stable, ρ is the density of overburdened rocks, b is the goaf span, l is a unit calculated width of the beam, is the limiting tensile stress of the rock mass, and , in which is the uniaxial compressive strength of rocks and k is the safety coefficient; b can be obtained from the cross-section of the iron deposit, i.e., Figure 4.