ABSTRACT:

Many investigators have studied the role of backfill as a ground support element. Understanding the rock-backfill interactions is essential to properly assess its role in the general stability of the mine workings as well as determining the proper design criteria for its design. The complexity of the problem is difficult to represent adequately in computers models as well as in physical modeling. To render the problem amenable to these approaches assumptions must be made to simplify the problem. There remains always some level of doubts weather the model is representative of the reality. In order to overcome these deficiencies, detailed and extensive field data would allow a better understanding of the backfill response. In this respect an extensive investigation was conducted by the authors to study in situ behaviour of mine backfill, in response to mining induced stresses. This investigation covered two mine sites over a span of 5 years. The first mine site was on a narrow vein type deposit and the second one a bulk type. The field program included various in situ instrumentations, in situ testing, laboratory testing, and a detailed geomechanical study of the sites followed by numerical simulations analysis. The role of the paste backfill is discussed in relation to the cases described, from the point of view of the rock mass-backfill interaction.

INTRODUCTION

The Bouchard-Hébert Mine is located approximately 20 km. NE of Rouyn-Noranda near St. Joseph de Cléricy, Québec. The mine is situated over the Abitibi Greenstone Belt. The Bouchard- Hébert Mine is situated within felsic to intermediate volcanic sequences alternating from volcanic debris flow to massive units. These assemblages show metamorphic alteration grading into the greenschist facies. The mine site is made up of complex shear zones associated with strong schistosity and foliation parallel to the regional stratigraphy of the volcanic units. The lenticular ore bearing zones are oriented parallel to the lineation which is in a SE orientation and dip steeply to the S direction. The schistosity and shear zones are associated with the ore zones. The typical stope has dimensions of 15 by 20 meters area with a height of up to 90 meters.

The second mine site, mine Chimo is located near Val-d?Or, Quebec. This mine is a narrow vein type orebody which involves strongly dipping stopes (70°) having a thin cross section of about 5 meters. Figures 1a and b illustrate the geometry of the stopes. The stopes were backfilled with cemented paste fill.

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