Post-earthquake groundwater hydraulic behavior in tunnels subjected to water inrush
Abstract
In the post-earthquake engineering setting, tunnel water inrush is controlled not only by water sources, but also by how fault and fracture pathways, excavation boundaries, and operation conditions reshape groundwater pressure. Here, we proposed a source-pathway constrained framework integrating an Almon-type distributed lag model, hydrochemical and isotopic constraints, mineral saturation screening, and three-dimensional groundwater simulations to characterize post-earthquake groundwater hydraulic behavior in the Mozi–Chayuan Tunnel, Southwest China. The event-adjusted distributed-lag model identified a primary significant rainfall-drainage response window of 35–76 d in tunnel 1/tunnel 1', whereas tunnel 2 showed no significant delayed response, confirming that rainfall acted mainly as delayed recharge rather than an immediate trigger. Hydrochemical facies, isotope-derived recharge elevations, and saturation-index patterns indicate the inrush water was predominantly meteoric-derived water supplied by adjacent catchments and shallow fractured aquifers, without evidence for a dominant deep saline or hydrothermal contribution. The simulations reveal a clear fluid-mechanical transition: excavation converted the tunnel into a near-zero-pressure drainage boundary, whereas lining and 8 m full-section grouting established a pressure-bearing boundary with pressure heads of approximately 70–110 m in the route-change section during operation. The fault-related damage zone and route-change section remained the main zones of pressure-head redistribution across all simulated conditions. Local piezometer validation at 4100 m yielded relative errors of 2.09% and 5.45%, supporting the reliability of the framework for post-seismic tunnel groundwater response assessment. This framework supports the safe operation and pressure-control design of the Mozi–Chayuan Tunnel and provides a transferable reference for assessing tunnel groundwater responses in earthquake-prone regions.