Seepage model experiments on urban tunnel influenced by dynamic and hydrostatic head

A new type of similar material for the surrounding rock-support system was developed to control the permeability coefficient, based on the Shenzhen East Transit Expressway Link Project adjacent to Shenzhen reservoir. A self-made seepage model test device was used to analyse the effects of dynamic and hydrostatic heads with different heights on water pressure, water discharge and seepage field. The results showed that when the groundwater level was relatively high, the inner walls of grouting ring underwent several procedures such as heavy wetting, the occurrence of saturation line, thoroughly wetting, overhanging water drops above the arch and intermittent water flow. With the decrease of the water head, the seepage velocity slowed down and the seepage time increased greatly. The water pressure at each feature point reduced approximately linearly with decreasing the height of the hydrostatic head. Besides, when the hydrostatic head became lower, the water pressure values at the same position of secondary lining and grouting ring were closer, and the dispersion of tunnel water discharge test was also smaller. Under the action of the dynamic head, the water pressure presented an obvious time lag, and the time effect was not conducive to the stability of the structure. The shallow buried areas were more easily affected by the decrease of the dynamic head, which indicated that it was necessary to strengthen the capacity and anti-seepage design of the tunnel roof. The water discharge of the tunnel exhibited a decreased tendency with the decrease of the dynamic head, and it took a longer time to reduce the same water-head difference.