Managing the Engineering, Health and Safety Aspects of Thin Spray- On Liner Application: Underground Trials at Xstrata Nickel Sudbury Operations, Nickel Rim South

Abstract: Bolts, shotcrete and mesh are today a part of the standard ground support system, although it becomes economically challenging to combine them sufficiently to support seismically active ground that requires increased yielding and energy-absorbing capabilities. An alternative to the current ground support system is the Thin Spray− On Liner (TSL) that may possess significant yielding properties. TSL has the potential ability to support seismically active ground in terms of deformation and rock bursting, common in deep mining.
This thesis is a part of the investigation; to prove whether the current formulation of the Thin Spray− On Liner could be implemented as an alternative ground support system and improve the support capabilities for complex ground types. The thesis will complete and deliver a conclusive trial site results summary.
A qualified ground control team put together a set of 11 large-scale trials in an underground environment within an active mine, Nickel Rim South in Sudbury. Each trial examined the geotechnical capabilities with respect to the engineering and health & safety aspects of the TSL. These trials are a Proof of Concept phase towards proving the liner as a superior component in underground rock support. This TSL was developed to achieve the de-bonding, toughness and tear resistant ground support parameters.
The thesis focuses on the specific geotechnical testing conducted at the Nickel Rim South Mine during the first quarter of 2012. Subsequent testing has been completed and liner development continues that is not covered within this thesis. Out of the 11 planned tests, 8 were executed during this period, and the rest will be executed later. Some of the results from the test trials are of a long− term nature and therefore the majority of the test results are not yet available. Before any tests could be executed, the isocyanate levels were measured and the results served as a base when setting up the PPE (Personal protective equipment) safety protocol. In addition some practical concerns arose during the trials, which were successfully solved after a few adjustments. The test results available for the full composite liner material concluded that peel− back at the leading edge next to the face blast, together with fly− rock damage, was severe, due to primer adhesion failure and this test was therefore considered to have failed. A comment should made in qualification of the above statement that the leading edge of the PCM(Polymeric Composite Membrane) was not bolted which was contrary to the project scope that suggested treating the PCM much like mesh prior to a blast and the wall was not high-pressure water scaled. The same test was performed on topcoat only, with significant improvement. The coverage of the topcoat only on top of shotcrete is poor, due to the pebbly nature and fibers protruding out from the shotcrete. The robot managed to apply the TSL with sufficient coverage and consistent thickness on the walls and the pillar nose, except for the edges where the guns flip over occurred and missed large perimeter patches, which was not dealt with till later in the testing.
These results indicate the requirement of a rehab procedure for damage caused to the liner, although the damage could partly appear due to the fact that the top coat could have been not yet fully cured and in its strength building process at the time of face blast. No determination was made of the PCMs actual strength required at the time of face blast during the cure cycle. There are speculations whether adhesion failure could be diminished by using a higher adhesion primer but without the foaming properties, which would result in a primer with lacking properties to fill the gaps for superior coverage while providing higher adhesion. In addition, bolting of the leading edge could be implemented to partially address the peeling issue. It is however important to investigate that the adhesion fails due to a rock failure and retains the loose material, unlike adhere and tear. The trial results are only investigated on the rock walls, in order to make a fair judgment on the liners performance and capability it should in addition be applied on the shoulders and the back to accomplish full rounds.