Investigation of Failure Mechanisms and Performance Optimization of Channel Seepage Control Layers in Cold Regions Under Coupled Wetting, Drying, Freezing, and Thawing Cycles

To address the degradation of seepage-control linings and structural instability of water-conveyance channels under coupled wetting-drying-freeze-thaw conditions in cold regions, this study investigated rehabilitated channels founded on expansive mudstone in northern Xinjiang. A two-dimensional transient finite-element model with fully coupled seepage, thermal, and mechanical fields was established in COMSOL Multiphysics 6.0 (COMSOL AB, Stockholm, Sweden) and validated against field monitoring data from three canal sections to explore the interactions among seepage evolution, frost-heave deformation, and structural responses over the full operational cycle. Numerical results showed that within five months after impoundment, the groundwater table in the channel foundation rose by approximately 4 m, supplying moisture for winter frost heave. During the four-month freezing period, the maximum frost-heave displacement reached 8 cm, and cyclic tensile stress could trigger geomembrane fatigue cracking mainly within the horizontal zone of 3.5–4.5 m along the channel base. In the subsequent phase after channel shutdown, foundation soil deformation increased to 16 cm, double the magnitude of initial frost heave, and the slope safety factor dropped to 1.305, implying an elevated landslide-failure risk. As a risk-mitigation measure, an acrylic polymer-based coating was adopted for surface seepage-control with favorable water-facing impermeability. Reverse seepage occurred above a backwater pressure of 0.01 MPa for unreinforced coatings, while this threshold can be enhanced by applying reinforcing fabric and interfacial agents. This work quantitatively identifies the progressive failure chain of seepage accumulation, frost heave, geomembrane rupture and slope instability, and evaluates the applicability and limitations of the proposed anti-seepage coating. It further elucidates bypass-seepage and reverse seepage hazards arising at coated-uncoated boundaries under partial surface-sealing schemes. The findings offer theoretical support and practical references for implementing a prevention-oriented strategy integrating surface waterproofing and internal drainage for cold-region water-conveyance infrastructure.