Study on the Influence of External Water Pressure on the Stress and Deformation of Prestressed Double-Layer Lining

In order to investigate the influence of external water pressure changes on the mechanical characteristics of prestressed double-layer lining, a three-dimensional finite element model of the prestressed doublelayer lining in a shield tunnel is established based on the Pearl River Delta Water Resources Allocation Project. The structural behavior and deformation of the double-layer lining during the prestressing construction and water flow operation stages are analyzed under different external water head heights (10 m, 20 m, 30 m, 40 m, 50 m). The results indicate the following: during the construction and operation stages, the overall shape of the double-layer lining exhibits an " elliptical" deformation pattern. When the external water head height decreases from 50 m to 10 m, the lateral deformation of the double-layer lining increases by 42.3%, the settlement at the crown decreases by 34.3%, and the uplift at the invert decreases by 42.4%. With the increase of external water pressure, the circumferential stress of the prestressed lining during the construction stage increases, and the tensile area of the segment lining during the operation stage decreases. The maximum circumferential tensile stress decreases by 54.05%. The prestressed double-layer lining tends to be in a hydrostatic pressure state, and the overall deformation pattern transitions from " elliptical deformation " to " overall contraction ". This study contributes to the safety of the double-layer lining structure.