Low quality rock is encountered in many manifestations in underground hard rock mines, ranging from weak and poorly consolidated rock to highly altered or foliated rock. Lateral mine developments driven in low quality rock pose on-going challenges to a mine operator, as ground stability issues, such as caving of under-supported ground, drift closure due to surface deformation or buckling processes, and degradation of exposed rock surfaces are a persistent concern.
For many operators, ground support design is an iterative process, as support practices are refined with time. This paper presents case examples of a rationales used to develop a support strategy for an isolated drift within squeezing Talc-Schist rock at depth. Field observations, numerical modelling simulation, and trials of a variety of support systems were used to assess conditions and to establish a path forward for long term stability.
In ground support applications, the goal of rock reinforcement is to limit the amount of closure around the opening while assisting the surrounding rock to reach a new state of equilibrium. In some mining applications, this equilibrium is difficult to attain since the openings are constantly subjected to bending moments and stress redistribution.
The rockmass examples from this paper can be considered as ‘‘mobile ground’’ where the combination of high ground stresses and a weak rock mass lead to the onset of closure soon after the opening has been created.
Attempts at preventing lateral deformation from occurring, using overly stiff support elements, such as resin rebar, are ineffective as the ground continues to deform around the individual elements. Since some deformation is inevitable, managing rather than preventing deformation is the goal of the rockmass support. The rockmass is reinforced with support elements which are sufficiently stiff to provide some degree of lateral confinement, while still permitting some ground movement.