With advances in fiber technology, shotcrete has become an essential support in the underground structures. The rock-shotcrete (R-S) interface plays a key role in determining the distribution of in-situ loads. This interface behavior is quite complex in reality and the interaction of interface of R-S play an important role in governing the bending moments and the thrust experienced by the shotcrete lining in tunnels and caverns. In the current study, an experimental procedure is presented to determine the deformational behavior and mechanical parameters of rock-shotcrete. Unconfined compression tests were performed on a composite material made of rock and steel fiber reinforced shotcrete (SFRS). Experiments were conducted with the consideration of stress conditions that prevail in most practical cases of underground opening. Cylindrical specimens were prepared using intact rock of Garnetiferous sillimanite gneiss and SFRS specimens obtained from the walls of underground tunnel. This paper discusses deformational behavior of rock, SFRS and R-S. The failure behavior of R-S is discussed and analytical calculations are presented, based on experimental observations on failure of R-S. The discussion will help in modeling of the R-S interface in numerical simulation, development of constitutive models for R-S and for better understanding of the R-S support system in underground structures.


In the field of rock mechanics, material properties is one of the pre-requisite for realistic numerical simulation of underground structures. Mechanical parameters of the materials influence the design of these structures to a large extent. These days, shotcrete has become one of the most important material to be used as a primary support system during lining of underground structures. The interaction between the shotcrete and rock plays a critical role in the transfer of stresses from the rockmass to shotcrete. There are only a few studies which discusses the rock-shotcrete interaction in detail. It has been shown by (Bae et al., 2003; 2004) through laboratory experiments and numerical simulations that the interfacial properties of rock mass and shotcrete exhibit time dependent behavior. However, in order to evaluate the mechanical interface properties, it has to be proven that the rock and shotcrete behaves as a composite material.

Various researchers have performed direct shear tests on different composite materials to determine the interfacial properties and shear behavior (Tong et al., 2016; Koupouli et al., 2016; Nasir and Fall, 2008, 2010; Saiang et al., 2005). The failure of shotcrete-rock under different loading conditions in the tunnels has been studied by Malmgren, 2008 and rock strength is found to be an influencing parameter.

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