Evaluation of the performance of the Po Shan drainage tunnels

Abstract

Po Shan Drainage Tunnels adapted a new drainage system technology in Hong Kong as well as in the other parts of the world which consists of underground drainage tunnels and sub-vertical drains. This dissertation studies the performance of the Po Shan drainage system and evaluates the effectiveness of drainage tunnel in groundwater control in slope. From the data analysis, it is concluded that the drainage system could effectively control the groundwater level by opening the mechanical valves in the sub-vertical drains. The hydrogeological condition observed in Po Shan area was also studied. From the piezometric readings, it is showed that significant different groundwater levels were observed from two piezometers installed at different depths in the same boreholes. The reasons as well as the implications of the phenomenon were discussed. It is concluded that the hydraulic gradient in the study area and other slopes in Hong Kong could be high and the piezometric levels should be corrected for non-hydrostatic condition especially in sloping ground.