A Metro tunnel in Shanghai crosses Bailianjing River, which is the third largest river in Shanghai. The foundations of the flood control walls of Bailianjing River are of square piles made of reinforced concrete, which stretch into the tunneling scope. Before the shield crosses the flood control walls, the pile foundations must be treated. In order to ensure reliable flood control and meet the requirements of shield boring across the flood control walls, firstly, temporary flood control walls made of bricks are built outside the existing flood control walls; secondly, the flood control walls within the tunneling scope are dismantled; thirdly, the piles that obstruct the shield boring are pulled out by shipmounted cranes; fourthly, mortar is filled into the pile holes and the disturbed ground is consolidated by means of mixing piles; fifthly, short piles are driven at the original positions to replace the square piles and the concrete of the top 50cm long part of the short piles are chiseled off, with the rebars being kept so as to be connected with the foundations to form an integral structure; finally, the upper wall body is built and the shield crosses the flood control walls when the required strength is achieved.