A Thin Spray-on Liner (TSL) is defined as a thin chemical based coating or layer that is applied onto the mining excavations with a thickness of 3 to 5 mm. Compared with traditional support systems, TSL applications can bring significant benefits to the operation such as low volume, rapid application and rapid curing. These properties will ease logistics, improve on cycle times, increase mechanization, and improve safety for underground support. Over the past 20 years, extensive research has been carried out to study the supporting capabilities and mechanisms of TSLs, mostly in hard rock applications; however, inadequate research has been performed for underground coal mine applications. This paper aims to examine the support mechanism of TSLs in underground coal mines through a laboratory approach. Three types of laboratory tests were carried out to study the performance of TSLs using coal samples: direct pull adhesion tests, coated core tests and indirect tensile strength (Brazilian) tests.
The effectiveness of ground support systems is important to the safety of personnel and equipment in underground coal mines. Over the years, various means have been applied to ensure the stability of roadways and excavations to meet the complex ground conditions in underground coal mines.
Mesh, shotcrete, mesh and shotcrete in combination, and shotcrete reinforced with various fibres are usually used for mining excavations as surface support (Stacey 2001, Archibald 2001). But the installation of mesh is labour intensive, expensive and time consuming (Tannant 2001), and it is difficult to automate to meet the rapid roadway development requirement (Nemcik et al. 2009). Shotcrete is chemically bonded to the rock surface and is able to achieve automation. However, shotcrete once sprayed onto the excavations, requires time to reach an effective supporting strength (Gilbert et al. 2010). The required thickness of shotcrete results in logistical problems for underground support (Tannant 2001, Laurence 2004). Besides, shotcrete may be considered too brittle in tension and shear in substantial ground deformations (Spearing 2001).