According to Bi Li Bi Li. Shanghai is a typical city affected by sediment. 1 0,000 years ago, the whole of Shanghai was still below sea level, so the soil water content in Shanghai was too high. After understanding the land structure of Shanghai, Soviet experts said that Shanghai is located in soft soil stratum with high water content and is not suitable for tunnel construction. Building a subway in a soil like Shanghai is like digging a hole in tofu. It collapses wherever it hits. At this time, Li Gancheng, vice mayor of Shanghai, pushed his way through the crowd and suggested that Shanghai still needed to conduct research and experiments, which persuaded everyone. It is under this historical background that Caobaolu Station started excavation and construction in order to lay the foundation for Shanghai subway construction and engineering test.