Abstract:

Pipe roof reinforcement allows safe excavation by creating longitudinal arching parallel to the tunnel axis. The complexity of boundary conditions of this method, however, imposes difficulties to understand the reinforcement mechanism. In this study, considering the delay effect of initial lining and revising the Winkler elastic foundation model, an analytical approach based on Pasternak elastic foundation beam theory for pipe roof reinforcement was put forward. With the example of a certain tunnel excavation, the comparison of the results between field monitoring, Winkler model and Pasternak model was made. The results indicate that the Pasternak model, which considering a more realistic hypothesis in the elastic soil than Winkler model, gives more accurate calculation and agrees better with the result of field monitoring, and is proved to be a better way to understand the reinforcement mechanism and improve design practice. The calculation results also reveal that reinforcing pipes act as levers, which increase longitudinal load transfer to an unexcavated area, and consequently decrease deformation and increases face stability.

Key words: tunnel, pipe roof reinforcement, Pasternak elastic foundation beam, field monitoring