Abstract
The application of Non-Explosive Expansion Materials (NEEM) has recently been increased in hard rock quarry mining, especially in granitic rocks. The most important mention in the quarry mining methods is determination of hole pattern, because it relates to cost of exploitation of the rock blocks, directly. It needs to predict the rock fracture process which it depends on the length of the first cracks and the growing to join together. A new algorithm has been suggested to evaluate of the first crack length by the linear elastic fracture mechanics (LEFM) theory. It requires determining a stress concentration factor which an experimental model has been utilized. A case study has been selected to verify of the numerical results which it is a granite mine in Iran. Numerical modeling has been applied to illustrate of rock fracture process and crack path and the results showed if the size of elements near the crack tip equal to grain size of the rock material or the ratio of the element length per diameter of the hole is selected about one per fifty, accuracy of the crack path prediction can be acceptable. On the other hand selection of an adequate rock slip criterion for crack planes is important, because of friction between two planes of a crack, plays an important role to predict of the crack growth. Also this research showed that Mohr-Coulomb criterion without cohesion is a suitable model for crack’s elements and Hoek-Brown failure criterion is an adequate model for rock substance.
Highlights
One of the main methods in quarry mining, especially in hard rocks, is the controlled fracture method that is carried out by the introduction of a slowly advancing crack by NonExplosive Expansion Material (NEEM)
Design of hole pattern in quarry mining is very important, because of it relates to cost of exploitation of the rock blocks
If two neighboring holes are enough close together, stress concentration will occur and it will cause to generation of first cracks
Summary
One of the main methods in quarry mining, especially in hard rocks, is the controlled fracture method that is carried out by the introduction of a slowly advancing crack by NonExplosive Expansion Material (NEEM). The method of rock breakage is without noise and vibrations and its operation, compared to blasting method, is more controllable, very safe and easy and without extra undesirable cracks in the rock block. In this method, some circular holes are drilled closely with equal length, diameter and spacing (center-to-center distance) in a rock block. The first condition to use of the linear elastic fracture mechanics theory (LEFM) is the material has to be brittle. Most of granites are brittle and the experimental results of the rock mechanics’ tests have shown the granite is brittle in this research
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