Cale DuBois, Doug McIlveen, Ken Pawliuk, Huma Chaudhry, Richard Brummer, Sami Jasem
Abstract At Cameco Corporations' Cigar Lake Project, large excavations are developed on 480 Level and
500 Level to host underground processing infrastructure that must remain stable for at least 15
years. Following the successful dewatering of the mine in October 2009, subsequent internal
rockmechanics investigations augmented by 3rd party technical investigations determined the
Water Flush Crusher/Run-of-Mine (WFC/ROMs) excavation required a rehabilitation strategy
to mitigate spalling of the WFC walls and intersection pillars. The mechanism of failure
propagating the movement of the excavation walls is understood to be controlled by the presence
of a dominant E-W striking and steeply dipping rock foliation wthin a relatively weak and
mildly altered rockmass sub-parallel in strike with 14 meters high walls and an intersection span
approaching 15 meters.
The application of open and resourceful communications between site mining engineers,
geologists, contract mining staff, construction management experts, corporate mining and civil
engineers, and 3rd party technical experts resulted in a multi-faceted short-term ground support
strategy consisting of standard bolting and screening, deep-seated modified-strand cable bolts
coupled with heavy gauge mesh straps, rockmass reconditioning using low-pressure grout
injection, and horizontal cable-lacing for the intersection pillars applied in lifts using a top-down
methodology. The intention of the short-term strategy was to stabilize the excavation so that a
long-term structural steel support installation - consisting of composite concrete walls, and arch
support applied to the side walls and crown of the back - could be constructed safely.
This paper summarizes the evolution of a short- and long-term ground support strategy and
criteria for the WFC/ROMs excavation developed using elements of civil, mining and
hydrogeologic design.
Keywords: Large excavation, Rock support, Cable bolt, Cable Lacing, Shotcrete, Grout, Rock Reinforcement
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