A Novel Ice-Plug Temporary Sealing Structural System for Deep Outlet Facilities: From Engineering Concept to Feasibility Assessment

Abstract

High-head deep outlets require temporary sealing methods that are reversible, rapidly deployable and mechanically reliable. This study proposes a novel in situ ice-plug structural system in which tunnel water upstream of the gate is frozen to form a temporary barrier, while the ice plug, concrete lining and surrounding rock act as a confined composite system to resist hydrostatic loading. The system is characterised as a load-transfer and stability problem governed jointly by ice compression, interfacial shear, lateral confinement and plug geometry, rather than by ice strength alone. The feasibility of the concept is evaluated through an analytical equilibrium formulation, two-stage physical model tests and complementary three-dimensional heat-transfer and nonlinear mechanical simulations. The tests demonstrate controllable condenser-pipe ice formation and provide pressure–displacement data for equivalent-parameter calibration, while identifying end sealing and ice–lining contact as critical constraints. Heat-transfer analysis shows that convection at the ice–water interface dominates cold-energy loss, whereas conduction into the lining and surrounding rock is secondary. Mechanical analyses reveal a predominantly compressive stress state and show that antisliding capacity is controlled primarily by interfacial resistance, surrounding-rock confinement and the plug length-to-diameter ratio. Under the adopted conditions, L/D = 0.4 is suggested as a preliminary lower bound for heads not exceeding 100 m. These findings clarify the governing thermal and mechanical mechanisms of the ice-plug–lining–rock system and provide a theoretical basis for preliminary design and further field-scale assessment.