Sustainable Lining for Underground Hard Rock Openings

Conventional cast-in-situ concrete linings are costly, time consuming and environmentally unfriendly solutions for supporting hard rock excavations, because concrete linings are unable to utilise the inherent strength of the rock. It is well understood that rock support is the application of a reactive force to the surface of an excavation such as concrete lining for example; whereas rock reinforcement is a means of conserving or improving the overall rockmass properties from within the rockmass by techniques such as rock bolts, cable bolts and ground anchors. This rock reinforcement strategy introduced to the tunnel roof and walls is considered to be a supporting element capable of sustaining a thrust at the arch ends. However, a potential small rock wedge failure is highly probable and may occur in between rock bolts. To deal with this issue, shotcrete linings will then be introduced acting as thin “protective skin” liners to support the rock surface with performance similar to a reinforced concrete slab. As the reinforced rock arch provides the required support to the opening, this shotcrete liner will then be designed to act as permanent protection cover and to comply with structural and durability requirements. Examples referenced in this paper demonstrate that the thickness of this shotcrete liner is relatively thinner than traditional concrete lining. Due to reduction of the permanent concrete lining thickness, the total excavation volume of caverns/tunnels is also reduced. As it minimises the use of cementitious products for permanent lining construction, thus leading to reduced CO2 emissions and lower energy.