Abstract
Problem statement: When the room and pillar mining method is adopted, the dimensioning of the rock pillars is one of the most important aspects that need to be faced from the engineering point of view. The available calculation methods are usually simplified and involve the areas of influence method for the evaluation of the mean axial stress induced in the pillar and the empirical formula to estimate the global strength of the pillar. Approach: A new probabilistic approach is proposed in this study concerning the evaluation of the degree of safety of a pillar, as far as rupture of the rock is concerned. This approach is based on the exact evaluation of the stress state inside the pillar and it takes into due consideration the typical uncertainty of the geomechanical parameters of the rock mass that makes up the pillar. Results and Conclusion: The pillar can therefore be dimensioned through an analysis of the cumulative probability distribution of the point safety factor in one or more points inside it.
Highlights
The determination of the safety degree of an underground rock pillar during room and pillar mining is one of the most interesting problems of rock engineering and rock mechanics and is one of the most frequently studied ones
This approach is based on the exact evaluation of the stress state inside the pillar and it takes into due consideration the typical uncertainty of the geomechanical parameters of the rock mass that makes up the pillar
The simplistic area of influence method can today be considered inadequate as an instrument for the dimensioning of rock pillars through a single global value of the safety factor: more sophisticated calculation methods that can indicate the stress conditions at each point inside the pillar and which can determine the value of point safety factors in the rock mass that makes up the pillar, are necessary
Summary
The determination of the safety degree of an underground rock pillar during room and pillar mining is one of the most interesting problems of rock engineering and rock mechanics and is one of the most frequently studied ones. An efficient way of working should involve a point evaluation of the stress state inside the pillar, but should adopt a probabilistic approach (Oreste, 2005a; 2005b; 2006) in order to be able to correctly represent the strength characteristics of the rock mass that makes up the pillar. A probabilistic analysis technique of the distribution of the safety factors inside a pillar is illustrated in this work This technique is based on the knowledge of the tri-dimensional stress state inside the pillar and on the strength characteristics of the rock, which are known with a certain degree of uncertainty
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