ABSTRACT:
Research was conducted to study the effects of artificial ground freezing on a hard rock mass. The research consisted of two case studies at the McArthur River Operation, each displaying a distinct response to artificial ground freezing. In one case, significant deformations were measured in adjacent excavations. In the second case, tensile stresses developed with negligible deformation measured. The expansion that occurs during the phase change from water to ice, and thermal stress from cooling of the rock mass, were proposed as the mechanisms responsible for the response of the rock mass. The research explored the various parameters that may have influenced the behaviour of the rock mass, and investigated ways of using this information to predict the behaviour of this rock mass to future artificial ground freezing programs.
1 INTRODUCTION
Many tunnelling and mining artificial ground freezing (AGF) projects have been conducted in a soil or very weak rock masses. In some unusual conditions, however, it is desirable to use artificial ground freezing in a hard rock mass. At the McArthur River Operation, a high-grade, underground uranium mine operated by Cameco Corporation, the geological conditions have created an environment that contains a high potential for water inflows into the mining areas if measures are not taken to mitigate these risks. Artificial ground freezing has been successfully applied to create a barrier between the excavations and the water source. Due to the scarcity of projects using artificial ground freezing in hard rock, there is limited information available in the literature on the behaviour of excavations in rock near artificially frozen ground; the majority of literature related to frozen rock mechanics involve studies on the seasonal freeze-thaw cycles, or the properties of frozen ground in the permafrost regions of the world.
