Prediction method for stress and deformation of pipe roofs and its engineering application

When the pipe roof is used to support the shallow soft surrounding rock in advance, the accurate prediction of the mechanical response of the pipe roof is an important basis to ensure the rationality of its structural design. Based on the elastic foundation beam analysis model for the pipe roof, considering the weakening of the pipe roof constraint caused by the instability section of the tunnel face, a pipe roof analysis model based on the Pasternak elastic foundation beam theory is established to predict the stress and deformation of the pipe roof during the excavation of the pre-support section. Using the governing equation for the Euler-Bernoulli beam and the constraint reaction distribution equation for the Pasternak elastic foundation, the analytical expressions for the force and deformation of the pipe roof under single-cycle footage are derived. By considering the dynamic process of tunnel construction, a method for calculating the mechanical response of the pipe roof in the whole length range is proposed. The influences of the main technical parameters such as the pipe diameter and excavation footage length on the mechanical response of the pipe roof are comprehensively analyzed. The results show that the excavation footage length is the key construction technical index to control the deformation of the pipe roof. Through the solution and application of the analysis model for the pipe roof, a more systematic analysis and prediction method is provided for the design and construction of the pipe roof.