13.5 Shanghai Metro Line 4 Seepage
In the early morning of July 1st，2003，a great amount of water and quicksand burst into the section of cross⁃river tunnel of Shanghai Rail Transit Line 4，which was a connection passage used to connect the upper and lower lines（as shown in Figure 13.9）.It caused about 270 m tunnel to be damaged and the ground settlement reached a maximum 7 m in the surrounding area，which caused three buildings heavily inclined.Even worse，the adjacent flood wall of Huangpu River collapsed and caused piping（as shown in Figure 13.10）.Fortunately，due to the timely alarm，all the personnel in the tunnel and nearby building were safely evacuated without causing casualties.However，the accident caused direct economic losses of around 150 million.
Figure 13.9 Aerial view of accident site
Figure 13.10 The collapsed flood wall of huangpu river
Due to the influence of ground settlement，the 30⁃meter⁃long cut⁃off wall at Dongjiadu Road section was sunk and cracked（as shown in Figure 13.11），which caused threat to flood control.The city rescue headquarters mobilized the armed police force to rush to the scene to take measures such as using sandbags and plugging，and timely controlled the danger.In addition，in order to protect the buildings in the surrounding areas，technical measures were adopted such as grouting to minimize the surging of underground quicksand.In order to balance the water and earth pressure inside and outside the tunnel，a method of closing the tunnel opening and injecting water is adopted.A large number of grouting filling and reinforcement were carried out for the roads and important buildings，large settlements on the ground were backfilled，and all the damaged buildings were demolished（as shown in Figure 13.12）.
Figure 13.11 Ground settlement
Figure 13.12 Heavily inclined buildings