Evaluating the behaviour of stiff polymer-modified cementitious thin spray-on liners from small and large scale testing

Abstract

The application of permanent areal support is recognised as a measure to either retain or prevent the mobilization of potentially unstable keyblocks between installed support elements. Various areal support methods have been developed to provide support to the freshly exposed area created by the blast and to provide support between existing support elements. These methods consist of either shotcrete, thin spray-on liners (TSL), blast resistant mesh or temporary (removable) nets. This paper focuses on the application of polymer-modified cementitious TSLs which is the type predominantly applied in South-African underground mines. Significant amounts of research has been conducted on TSLs. The majority of the research consisted of predominantly laboratory testing. The results of the tests only provide an output which can be used to measure a specific characteristic (i.e. tensile strength) against other products. The output obtained from laboratory tests are not understood, cannot be benchmarked against good or poor performing products or quantitatively related to the performance of the product when applied in-situ on a large scale. This situation is problematic as different support suppliers make claims in terms of the performance of their products based on a material property or small scale testing. The behavioural mechanism of a rockmass supported by TSLs is not understood. It is therefore not clear what critical TSL parameters will affect rockmass stability. Very little work has been conducted locally to test the in-situ behaviour of TSLs once applied. An extensive testing program was developed to establish how the material properties of a TSL as tested in a laboratory would relate to small and large scale in-situ behaviour. This paper discusses the testing conducted and the high level findings.