Mechanism and layout optimization of the longitudinal lining joints for frost-heave control in large arc-toe trapezoidal canals in cold regions

Longitudinal joints can serve as an effective measure to mitigate frost-heave damage to canal linings in cold regions. However, their design still relies heavily on the empirical mode at present. It is lacking in systematic theoretical and practical guidance. In this study, a numerical model of freezing soil was developed for canal frost-heave analysis, according to the thermo-hydro-mechanical coupling theory. The model also considered moisture migration, water-ice phase change, heat transfer, frost-heave deformation, and lining-foundation. A case study was taken as of the large arc-toe trapezoidal canal of the Fifth Main Canal in the Dayuzhang Irrigation District, Shandong Province, China. 153 longitudinal-joint layout schemes were constructed to vary the joint location, spacing (1–4 m), and number of joints (1–4). An evaluation framework was established to incorporate the maximum tensile stress in the lining, frost-heave deformation, and frost-heave nonuniformity. A systematic investigation was conducted to explore the influence patterns of longitudinal-joint layouts on the mechanical response of the lining. The results showed that: 1) Longitudinal joints subdivided the lining into independent panels, particularly with the deformation mode from integral bending to segmented tilting. The frost-heave deformation of the canal foundation soil was better accommodated to reduce frost-heave-induced stress in the lining. 2) When a single longitudinal joint was arranged at the canal bottom or on the canal slope, it only produced a local stress-relief effect in the region. Therefore, the first longitudinal joint was placed at the position of the maximum tensile stress in the lining, namely, the center of the canal bottom. With the first joint placed at the center of the canal bottom, the maximum tensile stress and nonuniform frost-heave deformation of the full cross-section first decreased and then increased, as the second longitudinal joint moved from the canal bottom toward the top of the canal slope. The optimal position of the second joint was corresponded to the newly formed position of the maximum tensile stress. The maximum tensile stress of the full cross-section was reduced to 0.96 MPa, with a reduction of 85.21%. The nonuniformity of frost-heave deformation was reduced by 97.18%. When multiple joints (no fewer than three) were arranged, according to the sequentially placing placement of joints at positions of the maximum tensile stress, the maximum tensile stress of the full cross-section was reduced to below 0.20 MPa, with a reduction rate of no less than 98.25%, and the reduction rate of frost-heave deformation nonuniformity exceeded 98.61%, indicating a significant frost-heave mitigation. 3) A lower water level and weaker frost-heave susceptibility of the soil were contributed to the optimal number of joints, whereas an increase in the elastic modulus of the joint-filling material increased the maximum tensile stress in the lining. The findings can provide a theoretical basis and guidance for the frost-heave mitigation of longitudinal joints in canals in cold regions.