Mining-induced deformation of potash yield pillars in the Cominco potash mine at Vanscoy, Saskatchewan, has been documented by mapping deformational structures, determining changes in pillar width and in thicknesses of potash and interbedded clay layers, and analyses of rock fabrics in samples collected from three yield pillars. Pillar deformation over a period of 8 years can be shown to have involved progressive bulk rock flattening, followed by development of shear zones at pillar corners, development of shear wedges at pillar margins, and detachment of these wedges into adjacent rooms. Furthermore, this sequence appears to be repetitive. Strain in halite involves fracturing and displacement and rotation of fragments, strain in sylvite is continuous, and grain boundary sliding has been an important mechanism in the deformation. Although the fabric anisotropy cannot be used to assess total bulk rock strain, the component of strain related to sylvite shape change has been examined during progressive failure of the pillars. The values of strain in the principal strain directions based on sylvite shape are estimated as 42% shortening in the subvertical direction, 37% subhorizontal elongation perpendicular to the original openings, and 25% subhorizontal elongation parallel to the original openings. Key words : yield pillar, potash, fabric analysis, induced deformation.
INCREASING THE EFFICIENCY OF ROOF BOLTING SUPPORTING CONVEYOR ROADWAY 555 PROTECTED BY A YIELD PILLAR IN THE CONDITIONS OF MINE CHERTINSKAYA-KOKSOVAYA
