Abstract:

Blockage of drainage holes in deep-buried hydraulic tunnels can significantly alter the pore-water pressure distribution and the mechanical response of the lining, thereby threatening tunnel stability and operational safety. Compared with conventional methods that represent blockage by uniformly reducing the permeability of drainage holes, this study proposes a segmented blockage modeling method based on line elements. A numerical seepage model for deep-buried tunnels is then established and validated its good applicability through comparative analyses. On this basis, an indirectly coupled seepage–stress procedure is employed to develop a load–structure model and to quantify the influence of the spatial distribution of blocked drainage holes on the load-bearing behavior of the lining. The results show that hydraulic damage in the lining induced by single-hole blockage follows a three-stage evolution: gradual change, abrupt increase, and stabilization. The corresponding critical blockage depths are 0 m, 3.6 m, and 4.4 m. Excessive hydraulic gradients near the blockage cause compressive deformation of the lining lead to the formation of an inflection point. At the end of the gradual stage, when the relative blockage depth reaches 0.9, tensile damage governs the failure of the lining, whereas compressive damage can be neglected. For adjacent multi-hole blockage, local external water pressure on the lining increases significantly, reaching a peak of approximately 3.81 MPa when two blocked holes are adjacent and decreasing to 2.65 MPa when they are widely spaced. The resulting highly non-uniform local high-pressure gradient is the dominant factor causing through-thickness damage. These findings provide a theoretical basis for optimal design, safe operation, and effective maintenance of drainage systems in deep-buried hydraulic tunnels.

Key words: hydraulic tunnel, lining structure, drain hole blockage, seepage-stress coupling, damage evolution, numerical simulation