Deformation-based support design for highly stressed ground with a focus on rockburst damage mitigation

As mines go deeper,mine designs become more fragile and effective rock support becomes a strategic element for ground control to facilitate timely construction and cost-effective access for uninterrupted production.This article focuses on the design of integrated support systems for brittle ground when large displacements due to gradual bulking of stress-fractured rock or sudden violent bulking during rockbursts are induced by static and dynamic loading.It provides an overview of support design principles for a rational approach to ground control in deep mines when large deformations are anticipated near excavations.Such designs must not only account for load equilibrium but also for deformation compatibility.Most importantly,the design approach must account for the fact that the support’s displacement capacity is being consumed as it is deformed after support installation.It is therefore necessary to design for the remnant support capacity,i.e.the capacity remaining when the support is needed.Furthermore,if the support capacity can be consumed,it can also be restored by means of preventive support maintenance(PSM).The PSM concept for cost-effective ground control is introduced and illustrated by quantitative and operational evidence.Contrary to other design approaches,the deformation-based support design(DBSD)approach provides the capacity of an integrated support system as a function of imposed displacements.Reduction in this support capacity due to mininginduced deformation renders excavations increasingly more vulnerable if located within the influence of active mining and seismic activity.Because deformation measurements are robust indicators of the decay in support capacity,scanning and other displacement monitoring technologies enable measurements to verify the DBSD approach,to assess the remnant safety margin of the deformed support,and to make operational support maintenance decisions.

An operational approach to ground control in deep mines

As mines go deeper and get larger,mine designs become more fragile largely due to the response of the rock mass to mining.Ground control and rock support become important levers in the mine construction schedule,production performance,and excavation health.For example,in cave mines,the production footprint together with associated mine infrastructure are significant investments in a modern caving operation.This investment must be protected and maintained to reduce the risk of ground-related production disruptions.It is necessary to preserve the health of these excavations and their maintenance through an effective rock support design.Rock support thus becomes a strategic element in asset management.This article focuses on support design for brittle ground when displacements induced by stress-fracturing consume much of the support’s capacity.It deals with the functionality of the support in deforming ground.Several interlinked concepts are important when assessing excavation health.Designs must not only account for load equilibrium but also for deformation compatibility and capacity consumption.Most importantly,the support’s displacement capacity is being consumed when the rock mass is deformed after support installation.Hence,it is necessary to design for the support capacity remaining at the time when the support is needed.If support capacity can be consumed,it can also be restored by means of preventive support maintenance(PSM).This concept for cost-effective ground control is introduced and illustrated on operational evidence.Furthermore,how design can impact construction costs and schedule are discussed.Support is installed to provide a safe environment and preserve an operationally functional excavation.It also must assure senior management that investments in high quality support and its maintenance will substantially reduce delays and with it,costs.It is demonstrated that the use of‘gabion-like’support systems can achieve these goals.A technical summary of the‘gabion panel’support system design is presented.