WATER-INRUSH PROCESSES OF THE KARST TUNNEL IN SOUTHWEST CHINA

A large number of karst aquifers are distributed in the southwest mountainous area of China, due to the complexity and inhomogeneity of the karst geological conditions, the occurrence of water-inrush and even mud-inflow is very frequent during the process of tunnel excavation. The water-inrush would not only cause casualties and postpones to the construction project, but also affect the regime of groundwater around the tunnel area.

Tunnel water-inrush in karst area have been well researched in recent decades, however, most of the researches focused on the total volume of inflowed water into the tunnels, systematic research of tunnel water-inrush processes and rule of water-inrush are still unrevealed. In this paper, 17 tunnels are selected as the typical object in the karst area of southwest China. Based on the logs of inflowed water volume (Q-T curve) into the tunnel in karst area of southwest China, the characteristics of tunnel water-inrush processes was analyzed and concluded, as well as the controlling factors of water-inrush event was summarized.

According to the cases of the 17 tunnels, 7 types of water-inrush process was concluded using the Q-T curve. The water-inrush process types are rainfall recharged rapid inrush type, rainfall recharged gentle inrush type, groundwater recharged synchronous inrush type, groundwater recharged hysteresis inrush type, dual-recharging synchronous inrush type, dual-recharging hysteresis inrush type and dual-recharging mixed inrush type.

On the basis of the water-inrush process type analysis, 6 models of the aquifer for water-inrush were summarized to the tunnels in karst area in southwestern China. The aquifer models are karst fracture model, karst pipe model, enclosed karst cavity model, karst fracture-karst pipe model, karst fracture-karst cavity model and fault-karst pipe model.

Lastly, the excavation process of XieMa tunnel in Chongqing was set as an example. According to the 3D Modflow simulation, the peak volume of inflowed water in the tunneling section lagged the peak value of rainfall for 295 days. It was claimed that the tunnel water-inrush type (Q-T curve) is the dual-recharging hysteresis inrush type, as the groundwater in karst pipe was another source for the inflowed water.