The soft soil within the pipe roof ahead of excavation face was generally reinforced for retaining the face stability, but the Beihong-Road tunnel in Shanghai constructed recently is the first case to adopt pipe roof method without reinforcing the saturated soft soil. It is made of 80Φ970 steel pipes with interlocks forming a rectangular type of pipe curtain. Stability of the excavation face and the controlling of ground settlement during construction are obtained by box grid and steel pipe roof. The heave of ground surface is produced during the box grid extruding into the soil as culvert box jacking forward. To study the mechanism of pipe roof, such as ground heave magnitude, range, uplift force and steel pipe flexural rigidity, pipe roof is simplified as longitudinal grade beam. The pipes ahead of grid bear uplift force within the range of passive sliding zone, and other parts of them lay on elastic foundation. This model can calculate heave magnitude, range and uplift force, etc.
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