Multi-Scale Numerical Model for Groundwater flow Simulation of a Karst Tunnel in Kunming,China

Due to the inhomogeneity of the carbonate rocks and discreteness of the karst water, delineation of the groundwater flow within karst area remains a challenging task as yet. Based on KunCheng tunnel of a water diversion project in KunMing, multi-scale groundwater flow models were set upto simulate the groundwater flow. Large scale model was used to obtain the boundary conditions and hydrogeological parameters, which were then assigned to the small scale model.The small scale model was generalized as an equivalent continuous medium, and two karst pipelines are established  by module River. After then,  the multi-scale numerical modelswere used to simulate the  groundwater seepage field and predict the recovery of groundwater after tunnel construction. The main results and conclusions are as follows.

(1)Black karst pipeline and white karst pipeline systems share one recharge source but have two independent discharge systems. The recharge source is the exposed karst rock in the northeast part of study area. Obstructed by aluminum clay rock of P₁d, groundwater discharge is divided into two parts during the runoff process.

(2)During the tunnel construction process, the water level at the exit of White karst pipeline reduced 9m in pipe model B₁ while reduced 10m in the solution fissure model B₂, both two models suggest that the tunnel construction will cause the drainage of White karst pipeline exit. The water level at the exit of black karst pipeline reduced 1m in pipe model B₁ while reduced 4m in the solution fissure model B₂.

(3)In model B₁, total water discharge during tunnel construction is 69876m³/d, in model B₂ , the total water discharge is 95817 m³/d  and  is much larger than model B₁ due to the quick groundwater transporting and exchange in karst pipeline..

(4)After the tunnel construction, exits of two pipelines and observation well see the water level recovery because of the formation sealing . The recovery trend is relatively rapid in the early stage, and slow in the later stage. It takes 8.5 years and 10 years for the exits of black and white pipelines and observation wells to reach the original water level, respectively. During the recovery process, groundwater exchange form was changing from pipe supplying aquifer to aquifer supplying pipe, which made model B₂ recovered faster than model B₁ in early stage, and vice versa.

Using large scale model combining with secondary scale model, and the module River to generalize karst pipeline can reflect the flow dynamic characteristics of karst pipeline effectively.