Evaluation of support characteristics of wet-mixed shotcrete with powder type cement mineral accelerator

Abstract

Instead of conventional in-situ cast concrete lining, permanent shotcrete lining is widely used. In order to secure the required performance of the shotcrete, the strength, deformability, durability, pumpability and rebound ratio are of great importance. In this study, the mechanical performance of high-strength shotcrete (wet-mixed shotcrete with powder type cement mineral accelerator) at the weathered rock condition was evaluated. In the performance analysis, the finite difference method (FLAC by Itasca) was used. The factor of safety of shotcrete lining against flexure was examined. When using the high-strength shotcrete, the factor of safety increased by a small amount. For the same factor of safety, however, the thickness of shotcrete could be remarkably reduced. In addition, the ground reaction curve analysis was carried out to examine the amount of displacement and time for the convergence. When using the high-strength shotcrete, the displacement at the crown and sidewalls decreased as much as 10%. Assuming the increased modulus of elasticity (25 GPa) of the high-strength shotcrete, the convergence was achieved at as early as 3 mm of displacement at the crown. In summary, the high-strength shotcrete showed more favourable mechanical performance than the conventional shotcrete. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.