BoardOur paper is concerned with the mine planning aspect of rockburst control. We did not intend to discuss destressing or increased fill modulus as means of controlling rockburst. I would like to explain a few matters not covered in the commentary, which did indeed cover most things. The previous mining method at the Star mine was a horizontal cut and fill method in which a flat backed pillar was created. The horizontal fill progressed up in a line toward the previously mined area above it, leaving the flat backed sill pillar. When this pillar is reduced below about 60 to 70 feet severe rockburst problems occur. The primary consideration in this paper, to make it immediately applicable in industry, was mainly the economics of the problem. We wished to devise a new mine design that would fit in directly with the present mining system, and hence must be a horizontal system, without affecting production, since the ore in the Star mine is marginal and any reduction in production could close the mine down. Economic considerations were dominant. The energy release rate design method involves nothing new. It is well documented in the literature, being first proposed by Cook at the 8th Symposium on Rock Mechanics. It is now used as a general design procedure in South Africa and accepted by mining companies throughout Africa. Hence we are doing nothing new in applying that design procedure to a mine here in the United States. What is new is a system we have arrived at of mining the center stopes approximately 50 ft. ahead of the two abutment stopes to get the lowest rate of energy release. This system could be fitted into existing practice at the Star mine with no change in machinery, and has now been operating for approximately 8 months and at the 7500 ft. level is now nearing completion. As our paper indicates the two center stopes are about 25-30 ft. from holing through the 7300 ft. level. At present we are trying to correlate the data that we are getting. We have installed a microseismic network which is now providing ample data. Previous records are not suitable to readily correlate with present data. However, the general feeling of personnel at the mine is that the severity of rockbursting has decreased significantly. More detailed conclusions will be possible in about a year. At present the 7500 ft. level is being finished and the same system is being implemented at the 7700 ft. level. With the microseismic system in operation it should be possible to obtain some correlation between the two levels. To put our paper in context I would like to first remark that at present there is only one commercial size oil shale mine in operation in America. This severely influences the design method since there is not a large data base from which to correlate pillar size and strength information as has been possible in the past in coal and some copper mines around the world.

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