Non-Darcian flow effect on discharge into a tunnel in karst aquifers

• Published in: International journal of rock mechanics and mining sciences (Oxford, England : 1997) England : 1997), 2020-06, Vol.130, p.104319, Article 104319
• Main Authors: Chen, Yi-Feng, Liao, Zhen, Zhou, Jia-Qing, Hu, Ran, Yang, Zhibing, Zhao, Xian-Jin, Wu, Xing-Liang, Yang, Xu-Lie
• Format: Article
• Language: English
• Subjects: Aquifer systems; Aquifers; Boreholes; Computational fluid dynamics; Computer simulation; Darcys law; Data interpretation; Discharge; Equilibrium flow; Evaluation; Fluid flow; Forchheimer equation; Groundwater; Groundwater flow; Hydraulic gradient; Karst; Karst aquifers; Mathematical models; Non-Darcian flow; Properties (attributes); Seepage; Statistical correlation; Tunnel construction; Tunnels; Water flow
• ISSN: 1365-1609; 1873-4545
• DOI: 10.1016/j.ijrmms.2020.104319

The groundwater flow in karst aquifers is prone to become non-Darcian due to the presence of karst conduits, and this effect may become more pronounced during tunnel construction. Prediction of discharge into tunnels in karst aquifers remains a challenging task because of the complex nature of non-Darcian flow and the uncertainty of aquifer's properties. This study aims to evaluate the effect of non-Darcian flow on the discharge into a tunnel in karst aquifers in Guizhou Province, China, where a large proportion (~86%) of borehole packer tests evidences the flow in non-Darcian regime. An integrated method combining packer test data interpretation, statistical correlation and inverse modelling is proposed to determine the non-Darcian flow properties of the aquifer system. Numerical simulations of steady-state flow show that the predicted discharge based on the Forchheimer's equation agrees better with measurements than that based on the Darcy's law by ~27%. The region with the most pronounced non-Darcian effect occurs at the intersection between the tunnel and a karstified fault connecting to an underground river, and the occurrence of non-Darcian flow leads to an increase in hydraulic gradient, but a reduction in discharge into the tunnel. This work presents a framework that combines aquifer properties estimation and numerical simulations for more accurately evaluating the discharge and seepage erosion risk induced by tunnel construction in karst aquifers. •Borehole packer test data evidence non-Darcian flow behavior in karst aquifers.•Determine aquifer properties by test data interpretation and statistic correlation.•Neglecting the non-Darcian flow effect overestimates tunnel discharge by ~27%.•Increase of flow nonlinearity leads to higher hydraulic gradient and erosion risk.