Shotcreting in Rock Excavation and its Adhesion Strength
Dheeraj Kumar et al.
Mining Department, Indian Institute of Technology, Kharagpur, India
In the present trend of support system used in underground coal-mines, shotcrete is gaining wide acceptance particularly in tunnel linings. The shotcrete support efficacy depends on the adhesion strength i.e. bonding between shotcrete and the rock surface. In order to determine the Bond Strength of shotcrete to rock surface, an instrumental setup has been devised. The different coal measure rocks like shale, sandstone (coarse, medium, and fine grained) were acquired from various mines. A thorough laboratory study of adhesion of shotcrete to same rock with different surfaces roughness shows that roughness of the rock surface play a more significant role in Bond Strength, for a particular range of JRC between 8 and 17. For a particular range of JRC Bond Strength is strongly correlated to JRC. The result also showed that tensile strength of rock has no relationship with Bond Strength. For a perfect bonding minimum setting time of shotcrete mixture is found to be 21 days. It was further investigated that the use of some accelerating material becomes significant in order to achieve full Bond Strength at the earliest. A minimum of five days is required to get an early setting of the shotcrete. The practical consequences of the investigation are also discussed.
KEYWORDS: shotcrete, bonding, tunnel lining
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