Structural And Mechanical Characteristics Of Double-Hoop Unbonded Annular Anchor Lining

A new type of prestressed reinforced concrete lining with double-hoop unbonded annular anchors (hereinafter referred to as "DUAA lining") can resist high internal pressure. It provides an approach to solving the problem of supporting large-section pressure tunnels with thin cover layers, unsatisfied stability, and high internal water pressure. However, its extensive application was hindered by its uncertain mechanical properties caused by its complexity. A large in-place test of the mechanical properties of the DUAA lining was carried out in a 6.8 m diameter water conveyance tunnel in Jilin, China. The study reveals the superposition effect of the annular anchor tension, the spatial distribution patterns of the prestress, and the potential failure mode of the structure by closely considering the mechanical properties and the prestress increasing together. The annular anchors are closed at the free anchor head, which not only helps decrease the prestress loss but also improves its uniform distribution. Although the annular anchor in different positions generates different prestress effects for the DUAA lining, the total prestress value by adding all the annular anchors is close. For the active restriction of the annular anchor, the relatively uniform circular and longitudinal prestress generated from the DUAA lining can effectively resist high internal water pressure even without the support of the surrounding rocks.