Abstract
SYNOPSIS Thin spray-on liners (TSLs) have been used as sealants and rock support in tunnels for over 25 years. Laboratory tests have indicated satisfactory properties that can provide adequate strength, adhesion, toughness, and elasticity as part of rock support systems in mining excavations. These characteristics are, however, not always demonstrated in practice, when mine environmental conditions do not correspond with laboratory environmental conditions. The shortcomings of TSLs experienced in the mining industry have raised concerns, resulting in scepticism from some operators regarding their utilization. The research described in this paper aims to investigate TSL performance in environmental conditions similar to those experienced in mines. Brazilian indirect tensile (BIT) specimens were prepared from precast shotcrete and coated with TSLs. The specimens were then exposed to different environmental conditions for up to 112 days before BIT testing under various conditions: laboratory room temperature and humidity; saturated room temperature; and combined saturated and high temperature (50°C). Additional uncoated shotcrete and TSL BIT specimens were prepared for comparison purposes. The results of the BIT tests showed that environmental conditions have a significant influence on the tensile strength enhancement of shotcrete by TSLs. Water-based TSLs are most likely to be suitable for high humidity environments, although their performance decreases at higher temperatures. Numerical modelling of TSL-coated BIT samples confirms the potential limitations of designing TSL support based only on laboratory testing carried out under room conditions. Keywords: thin spray-on liner, Brazilian indirect tensile (BIT) test, TSL performance, environmental conditions, humidity, high temperature.
Highlights
Accidents in underground mines are often rockfall related (Potvin, Stacey, and Hadjigeorgiou, 2004)
Previous publications have indicated that thin spray-on liner (TSL) can provide significant benefit in the support of underground excavations in rock masses
Most TSL test data reported in the literature has been obtained in ’standard’ room temperature and humidity environments, which are not typical of conditions in deep mines
Summary
Accidents in underground mines are often rockfall related (Potvin, Stacey, and Hadjigeorgiou, 2004). To reduce accidents to a zero-harm target, various rock support techniques have been implemented and improved Reinforcement supports such as frictional anchors, mechanically anchored rockbolts, and untensioned grouted dowels are common. Containment support such as shotcrete, wire mesh, and straps (Hoek, Kaiser, and Bawden, 2000; Stacey, 2001) has been utilized to accommodate the rock mass displacement. These supports have shown advantages and limitations, depending on the rock mass qualities and mechanisms of rock mass failure. With regard to practical implementation in mines, TSLs provide rapid curing (Yilmaz, 2010) and simplicity of utilization and transportation, owing to the compact equipment size and the small volumes of TSL materials required
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