Abstract:Up to now,the subway crossing project through Hongxu Road is a pipe-roof project with largest cross-section box culvert in the world. It is constructed in saturated soft soil stratum in the Beihong Road located in the middle ring-road in Shanghai. Based on restrictions of ground settlement and extremely dangerous potential sliding condition on soil in front of the box culvert during the culvert being pushed slowly and some soil being excavated,support effect of upper pipe-proof is analyzed in order that mechanical characteristics of the pipe-roof can be completely known. Because different segments of these pipes have different mechanical status,they are analyzed mainly by supported beam model with two fixed ends and beam on elastic foundation model. Support effect of the upper and middle pipe is analyzed in detail in the practical project. The results show that the pipe-roof plays an important mechanical role in the course of the culvert being pushed. It can support quite a little weight of soil on it so that only partial weight will transfer to the stratum under it. So the pipe-roof can be benefit for economic and rational design of steel grids inverted in the front of the culvert for stabilizing the cutting surface.