Waterproofing Solutions for Metro Tunnels

Almost all underground structures suffer from water leakage problems. Traditional methods using injection for waterproofing in underground metro tunnels can only reduce large water leakages; they are not effective in preventing water from seeping into the tunnel. In addition, traditional injection methods cannot prevent reinforcing steel corrosion in concrete structures. The reinforcing steel can expand by twice its original volume after reacting with water and oxygen in producing ferric hydroxide. This phenomenon causes deterioration and spalling of concrete cover around the reinforcing steel. If this problem is not attended to, the longer-term structural integrity of the tunnel will be impaired. An innovative solution making use of the electro-osmosis theory has been devised and implemented in the London Underground and the MTR in Hong Kong. It is an effective way of keeping underground structures dry, and at the same time, protecting the structural integrity of reinforced concrete. This paper discusses how the electro-osmosis theory can be applied to these structures and offers examples demonstrating how the technology can be applied in real situations.