Role of Shear Deformability on the Response of Tunnels and Pipelines to Single and Twin Tunneling

Tunneling can compromise the safety and serviceability of existing buried infrastructure because of settlements, crack openings, dislocations, and material strains. A continuum-based soil-structure interaction model, implementing an equivalent Timoshenko beam, is used to evaluate the excavation-induced settlements and longitudinal deformations of existing tunnels and pipelines. Both single and twin tunneling scenarios are examined. The shear flexibility of shield and sprayed concrete lining tunnels may be significant. This increases tunneling-induced settlements while it decreases tilt, curvature, and the associated bending moment, with implications for optimal monitoring installations. In this work, a new dimensionless shear factor is introduced, governing the relative importance of shear and bending deformations and accounting for the settlement trough width. This can be used to evaluate if a pure-bending, shear-dominated, or mixed deformation mode should be expected. Design charts to assess existing infrastructure affected by either single or twin tunnels are proposed. (c) 2021 American Society of Civil Engineers.

Automated summary

This study examines the impact of tunneling on existing tunnels and pipelines using a continuum-based model and introduces a new shear factor to evaluate different deformation modes. The research found that the shear flexibility significantly affects tunneling-induced settlements and also influences tilt, curvature, and bending moment.