Influence of glacitectonic fractures on wall failure in open excavations: Heath Steele Mines, New Brunswick, Canada

Abstract

Recognition and detailed mapping of glacigenic fractures and reactivated joints, along with such glacigenic features as striae and till fabrics, prove critical in predicting ground control hazards such as pit wall failure. Following a period of heavy rain in the autumn of 1991, a failure occured on part of the wall of an open-pit mining operation on the Heath Steel Mines property. The failure surfaces bounding the complex landslips of the pit wall were all either original glacigenic fractures or other joints reactivated during Late Wisconsinan glacier overriding. Apart from differential movement, such features include joints filled with coarse sand or clay. Comparaison of the geometry of glacigenic fractures in failed areas with the same features in areas just as densely fractured, but which did not fail, reveal a combination of circumstances where failure was predictable. In this case failure of an unstable rock mass resulted from unfavourable kinematic relationships involving the following: the low strength of clay- and sand-filled joints, the presence of highly permeable and weathered joint conduits, the unfavourable geometry between wall and joint orientation, and an occurrence of increased fluid pressure along the joints from high rainfall that triggered movement. Key words: glacitectonics, geotechnical, wall failure, excavations, rock-quality data, instability.