Safety Threshold Assessment for Carriageway Grooving in the Prestressed Concrete Lining of a Water Delivery Shield Tunnel

A special measure of carriageway grooving in the prestressed concrete lining of a water delivery shield tunnel locally weakens the cross-section, raising issues concerning the safe operation of the tunnel under high internal water pressure and the treatment/repair of grooving. Based on an actual project, a 3D finite element model containing the surrounding rock, shield segment and prestressed concrete lining was established, and the numerical results were compared with field-monitoring results of the ungrooved section. Parametric analyses were carried out on the loading behavior of the prestressed concrete lining with different depths and widths of the groove at construction and water-filling stages, under the assumption of the maximum continuous longitudinal length of the groove corresponding to the length of a standard lining segment. Results indicate that groove depth mainly governs circumferential compressive-stress concentration in the outer layer beneath the groove, whereas groove width governs the inner-surface longitudinal tensile-stress threshold along the central line of the carriageway. When the depth and width of the groove are limited within the carriageway to maintain the ring integrity of the prestressed concrete lining, the maximum inner-surface tensile stresses are lower than the tensile strength of concrete at the construction stage, and the circumferential stresses remain compressive around the full ring at the water-filling stage.