Study on regional nonlinear seepage flow combining indoor tests and numerical simulation

The Xixiayuan area on the northern bank of the Yellow River in Luoyang, Henan Province, China, is characterized by a typical riverbank dual-structure aquifer system with high permeability. The Yellow River boundary water level is elevated, resulting in strong inward recharge within the region. In seepage analysis and modelling, the influence of non-Darcy effects cannot be neglected. However, most seepage problems are still directly simplified as linear flow, which can lead to substantial errors. In this study, a local-scale physical model test is used to investigate nonlinear seepage behaviour at the local scale, and two parameters are proposed to identify flow regime transitions: the nonlinear hydraulic conductivity K F and the non-Darcy effect parameter δ , which quantifies the degree of nonlinearity. To further assess the impact of nonlinear seepage on regional-scale groundwater level distribution, a nonlinear partial differential governing equation is derived from the Forchheimer equation. A numerical simulation code is then developed to model the nonlinear seepage field at the regional scale; it directly uses parameters obtained from indoor tests without additional adjustment of fluid or medium properties, thereby avoiding secondary parameter tuning. These findings provide a new approach for mechanistic investigation and numerical simulation of similar nonlinear seepage fields. Field sampling were used to investigate the nonlinear seepage behaviour of the sand–gravel medium at the local scale. Analysis of the test data and parameter K F trends shows that, owing to the granular structure of the sand–gravel deposits, seepage within the porous matrix tends to become nonlinear even at relatively low seepage velocities. Building on these results, a regional seepage field was simulated numerically. Using field observations as the benchmark, the independently developed regional-scale nonlinear seepage model reproduces the actual seepage conditions more accurately than a conventional linear model, reducing inflow prediction errors by approximately 40 % and producing maximum hydraulic gradients along the excavation slope that are about 16 % higher. These results have practical implications for hydraulic design in riverbank engineering and for preventing and mitigating seepage-induced failures. • Novel quantitative indicators for nonlinear seepage are proposed. • Developed a regional seepage-field simulator incorporating nonlinear seepage. • Directly applied local-scale test parameters to regional numerical modeling. • Nonlinear seepage modeling reduces inflow prediction error by 40 % versus linear.