Two-way coupled transient hydro-mechanical response around deep pressure tunnels in viscoelastic-plastic soils

Pressure tunnels are typically deeply buried and equipped with permeable pressure-relief linings, accompanied by distinct transient seepage during initial operation and under sudden inner head fluctuations. Transient hydraulic loading can cause significant stress variations and deformations in soft soils surrounding tunnels, further complicating long-term tunnel stability maintenance. This study extends conventional theoretical solutions for consolidation in rheological soils by explicitly accounting for the rheological strain rate, and develops a two-way coupled hydro-mechanical semi-analytical framework for deep pressure tunnels by fully considering the viscoelastic-plastic properties of surrounding soils. Furthermore, the proposed framework is theoretically extended to evaluate the coupled hydro-mechanical responses around twin shallow tunnels subjected to dynamic traffic loadings, by integrating the improved image method with the Schwarz iteration method. Additionally, the Laurent series is utilized to deal with shallow tunnels in arbitrary cross-sections. The results indicate that the improved rheological scheme predicts faster consolidation and steeper pore pressure gradients than conventional methods. The evolutions of soil properties due to transient seepage are found to delay the consolidation process. Additionally, compared to conventional elastic–plastic models, the proposed viscoelastic-plastic framework produces smaller accumulated volumetric and deviatoric strains, providing more realistic deformation estimates for rheological soft soils under transient hydraulic loading. Parametric studies further reveal that the geometrical and mechanical conditions have significant effects on transient hydro-mechanical responses of soils surrounding tunnels. This work provides a flexible and efficient framework for analyzing two-way coupled transient hydro-mechanical behaviours of soft soils around deep pressure tunnels.