Most of the analytical and numerical models of tunnel groundwater inflow ignore the excavation process, leading to inaccurate prediction of discharge rate. A dynamic modeling approach was introduced by redevelopment of MODFLOW to simulate the change of groundwater flow step by step in accord with tunnel excavation. The drilling tunnel was conceptualized as a changing boundary condition, which was modeled by dividing the drilling process into a series of successive steps. The impact of permeability heterogeneity on groundwater flow was studied through a comparison between a homogeneous hydraulic conductivity case and a synthetic heterogeneous one. It was found that the discharge rate at drilling front kept stable in the homogeneous case, resulting in a linear increase in the total discharge rate, similar to the analytical solution by Perrochet (2005). In contrast, the front and total discharge rate were influenced significantly by the variability of permeability in the heterogeneous case. The time-dependent discharge rate at a given place was subject to an exponential decay for both cases with the maximum inflow occuring at the beginning of excavation. The relationship between discharge rate and hydraulic properties was further investigated in a high-K zone. It revealed that maximum discharge rate was proportional to hydraulic conductivity (K) and specific storage (Ss). The decaying rate of discharge was time-dependent and also proportional to the value of K and Ss. The water budget analysis demonstrated that water released from storage of the high-K zone was the major source of tunnel discharge at early times.

The use of either analytical or numerical models of groundwater inflow into a tunnel, ignoring the excavation process, will result in inaccurate prediction. More researchers have begun to study prediction methods with temporal and spatial variables, in accompaniment with the tunnel excavation progress. The hydrogeological parameters significantly affect tunnel inflow prediction; thus, it is always worthy to carry out an inversion analysis when the inflow rate observation is available for the excavated part of a tunnel. Based on a transient analytical model and the Trust Region Reflection (TRR) algorithm, this paper proposes a Dynamic Parameter Calibration (DPC) method to sequentially optimize parameters for a tunnel that is divided into several sectors. The results of two case studies indicate that the fitting effects by DPC are significantly improved compared with the empirical trial-and-error method, indicating good optimizations. The proposed scheme can conduct calibration simultaneously for multiple tunnel sectors and also several optimizations for the same sector. The parameter optimization results reflect the lithologic heterogeneity of different strata. Parameter sensitivity analysis proves that the hydraulic conductivity K has a greater influence on water inflow calculation than the specific storage coefficient S.

The drainage of groundwater in mountainous tunnel projects always leads to substantial decline of the regional water table, which may induce numerous environmental issues, such as spring depletion, surface subsidence, vegetation degradation, and impacts on local water supplies, especially in the enclosed karst aquifers of anticlines in the area, such as the Jura mountain type. A systematic hydrological monitoring was conducted during the excavation of the Wufu Tunnel in Chongqing, China. The monitoring data includes discharge rate and water level collected from tunnels, boreholes, coal mines, springs, and ponds, respectively. Hydrological responses of karst aquifers and surface water bodies to tunnel drainage and precipitation were investigated by statistical analysis, Mann–Kendall test, heat map, and wavelet analysis. Results show that the enclosed karst water system has strong hydraulic connections and good water storage conditions. Tunnel drainage is the dominant factor causing dynamic changes at monitoring points, while the influence of rainfall is relatively limited. Borehole water levels and coal mine drainage have a close correlation with tunnel inflow, while springs are influenced by both rainfall and tunnel drainage. Few pond monitoring points are related to rainfall. Tunnel drainage has transformed the regional groundwater dynamic conditions, causing local groundwater flow direction reversal and reconstructing the groundwater recharge-flow-discharge pattern.

The Sichuan Basin, having undergone multi-stage tectonic evolution, provides an ideal site to study structure-fluid interactions. Based on the collection of more than 200 hydrochemical datasets of various Middle-Lower Triassic karst groundwater, ion ratios, stable isotopes and Principal component analysis (PCA) were combined to quantify hydrogeochemical processes and to reveal structural controls on groundwater circulation and regional hydrochemical differentiation. Results show that the Huayingshan Fault (HYF) and Mingyueshan Anticline (MYAc) act as key first and secondary boundaries that divide the groundwater systems into different environments. Tectonics drove the groundwater to evolve through at most four stages, namely the residual paleo-seawater, chloride-dominated dissolution, sulfate-dominated dissolution and carbonate-dominated dissolution. Two groundwater circulation conceptual models were established for the Eastern Sichuan Fold Belt (ESFB). High-steep elongated anticlines with intense river incision have high structural permeability and active groundwater circulation, while short-axis anticlines under strong compression and lack large-scale river dissection, leading to shallower circulating depth. This study demonstrates that tectonic deformation intensity regulates groundwater circulation pattern, thereby governing hydrochemistry evolution.