Geomechanical Analysis of Tunnel Excavation in Strain-Softening Rock Masses

The geomechanical analysis of tunnel excavation in strain-softening rock masses addresses the challenge posed by the progressive reduction of strength after peak stress. In deep tunnels and roadways, excavation induces stress redistribution and deformation that evolve through elastic, plastic and softening phases. Accurate prediction of ground response curves and support requirements relies on advanced constitutive models that capture brittle failure, post-peak degradation and dilatancy. Analytical solutions, often based on cavity expansion or convergence–confinement methods, provide closed-form expressions for stress, displacement and plastic zone radii. Numerical approaches, including finite element and finite strain procedures, offer detailed simulation of stress-strain paths, support interaction and boundary effects. Integrating theory and computation has led to improved ground support design, optimised installation timing and enhanced safety in demanding geological conditions. This field of research underpins the global development of tunnels for transport, hydropower and mining, where reliable estimates of deformation and load capacity are essential to minimise risk and cost.

Research from Nature Portfolio

Recent studies have derived an elastic–plastic analytical solution for circular tunnels subject to non-axisymmetric external loads. The new formulation simultaneously yields the secondary stress field and excavation-induced displacement, and it reduces exactly to the classical axisymmetric case. Numerical validation demonstrates close agreement with finite-element results, offering a robust tool for theoretical design in complex loading scenarios. Another work has examined rock–support interaction in tunnels constructed by the New Austrian Tunnelling Method. Using three-dimensional numerical models, researchers quantified the support constraint effect and boundary influences, recommending an increase in support force by 2–3 % and an extension of model boundaries to 1.5 times the span for realistic convergence predictions. Field monitoring data from a major project confirmed that incorporating these adjustments yields numerical outputs in better accord with observed ground behaviour.

Geomechanical Analysis of Tunnel Excavation in Strain-Softening Rock Masses publication trend

The graph below shows the total number of articles in geomechanical analysis of tunnel excavation in strain-softening rock masses across all publications each year (not limited to Nature Index journals).

Technical terms

Strain softening: Progressive reduction of material strength and stiffness beyond peak stress.

Convergence–confinement method: A design approach that relates tunnel wall displacement to lining pressure via ground reaction curves.

Ground reaction curve: A plot of support pressure against tunnel convergence, reflecting the evolving stiffness of rock mass.

Plastic zone: The region around an excavation where rock has yielded and undergone irreversible deformation.

Dilatancy: Volume increase of rock mass upon shearing, often accompanying plastic yielding and fracturing.

Intermediate principal stress: The second-largest principal stress, which influences yield and post-peak behaviour in three-dimensional stress states.

References

1. An new elastic–plastic analytical solution of circular tunnel under non-axisymmetric conditions. Scientific Reports (2022).
2. Investigation of the support constraint effect and failure instability law of tunnels constructed using the New Austrian tunneling method. Scientific Reports (2022).
3. Elastic–plastic criterion solution of deep roadway surrounding rock based on intermediate principal stress and Drucker–Prager criterion. Energy Science & Engineering (2024).
4. A New Numerical Finite Strain Procedure for a Circular Tunnel Excavated in Strain-Softening Rock Masses and Its Engineering Application. Applied Sciences (2022).
5. A New Unified Solution for Circular Tunnels Based on Generalized SMP Criterion considering the Strain Softening and Dilatancy. Advances in Civil Engineering (2019).