Abstract
Falling or sliding of loose blocks is one of the most common failure modes in a rock tunnel. For tunnels in hard and jointed rock, fibre-reinforced shotcrete (sprayed concrete) in combination with rock bolts is one of the most commonly used supports to prevent such failures. The structural behaviour, and especially the failure, of this type of rock support, is complex and involves several failure mechanisms; such as cracking of the shotcrete and interface failure along the shotcrete-rock, bolt-grout and rock-grout interface. Therefore, rock supports are normally designed using analytical solutions based on the independent failure modes. However, these failure modes are derived based on experimental testing and the assumption that no interaction between the failure modes occur. This assumption has not been verified. Therefore, this paper presents a numerical model capable of simulating the failure of a bolt-anchored and fibre-reinforced shotcrete lining. The model includes bond failure between shotcrete and rock, cracking of the shotcrete and pull-out failure of rock bolts. The structural behaviour for each failure mode and the complete structure have been verified against experiments from the literature. This shows that the model is capable of simulating the different phases of failure, and show good agreement with results from full-scale experimental tests from the literature. Furthermore, results from the numerical simulation confirms that the design of the shotcrete lining can be based on individual failure mechanisms. Moreover, it was shown that a design based on the residual strength of the fibre-reinforced shotcrete is conservative compared to a design based on the bond strength.
Highlights
Fibre-reinforced shotcrete in combination with rock bolts is one of the most common ways to support tunnels in hard and jointed rock of good quality
This paper investigates the structural behaviour for a bolt-anchored fibre-reinforced shotcrete (FRS) lining and explains its failure mechanisms
A bolt-anchored and fibre-reinforced shotcrete (FRS) lining is commonly designed to be able to sustain the load from a loose block
Summary
Fibre-reinforced shotcrete (sprayed concrete) in combination with rock bolts is one of the most common ways to support tunnels in hard and jointed rock of good quality. The structural behaviour, and especially the failure, of the rock support is complex and involves failure mechanisms such as; cracking of the shotcrete and failures along the shotcrete-rock, bolt-grout and rock-grout interfaces. The structural behaviour and post-cracking response of fibre reinforced concrete and shotcrete have been studied by, e.g. Banthia et al [12,13] and Barros et al [14,15]. This paper investigates the structural behaviour for a bolt-anchored FRS lining and explains its failure mechanisms. Each failure mechanism contribution to the structural capacity of the support and the interaction between the individual mechanisms, i.e. the bond between shotcrete and rock, cracking of FRS and pull-out of rock bolts, is investigated. The paper is structured as follows: Section 2 presents the implementation, calibration and verification of numerical models for the individual failure mechanism.
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