Abstract
Problem statement: The strength of rock pillars in the presence of single, persistent, natural discontinuities can seriously be compromised and lead the pillar to collapse because of instability along the discontinuity itself. Approach: A specific analysis method for this kind of problem has been set up in this study to evaluate the stability of pillars and to determine the dimension that this kind of pillar should have in order to guarantee the minimum requested safety factor. Results and Conclusion: The objective is to determine the limit shear stress and the actual acting shear stress at 25 points distributed along the discontinuity in order to then be able to obtain the safety factor concerning collapse of the pillar along the discontinuity surface.
Highlights
The room and pillar mining method is one of the most common in the underground mining of mineralised rock of poor specific value and of mediumelevated mechanical strength (A’ssim and Xing, 2010)
The dimensioning of the rock pillars is one of the most interesting problems of rock mechanics and in the past was conducted using empiric formulas to evaluate the strength of the pillars and simplified formulas to determine the mean axial stress
Jaeger method (Jaeger and Cook, 1976), found the safety factor pertaining to kinematics along a single persistent natural discontinuity with a variation of its dip to the horizontal and of the mean horizontal confinement stress existing in the pillar Eq 1: stress existing in each point, it is possible to determine the local safety factor at each point inside the rock pillar
Summary
The room and pillar mining method is one of the most common in the underground mining of mineralised rock of poor specific value and of mediumelevated mechanical strength (A’ssim and Xing, 2010). The dimensioning is developed imposing that the minimum local safety factor is above a pre- This procedure is efficacious and reliable, even when natural and not very persistent discontinuities, which can be oriented and distributed in various directions in the rock mass, are present. The stress state inside a rock pillar: Eighteen tridimensional numerical tables have been set up to perform a detailed analysis of the stress state that discontinuity and to determine the safety factor develops inside rock pillars. These tables make it along the discontinuity. Half-width Half-interaxis Mid-height Total height Model of the pillars of the pillars of the pillars of the number (wp/2) (m) (i/2) (m)
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