A new criterion for defining tunnel portal failure using the strength reduction method

Area of Science:

• Geotechnical Engineering
• Tunnel Engineering
• Computational Mechanics

Background:

• The strength reduction method (SRM) is increasingly used for tunnel portal stability analysis.
• Selecting an appropriate failure criterion is crucial for the accuracy of SRM analysis.
• Traditional criteria have limitations in application, quantification, and mechanical interpretation.

Purpose of the Study:

• To evaluate traditional failure criteria used with SRM for tunnel portals.
• To propose and validate a novel variational criterion for tunnel portal stability analysis.
• To assess the robustness and efficiency of the proposed variational criterion.

Main Methods:

• Analysis of traditional failure criteria (displacement mutation, plastic zone penetration, non-convergence, energy mutation).
• Development and implementation of a new variational criterion.
• Validation using numerical models and comparison with traditional criteria.

Main Results:

• Traditional criteria exhibit drawbacks: cumbersome application, lack of clear standards, absence of mechanical basis, and high computational cost.
• The proposed variational criterion effectively identifies failure mechanisms.
• The variational criterion demonstrates high accuracy (≤1.6% relative error) and robustness across various parameters (mesh density, geometry, material properties).

Conclusions:

• The variational criterion overcomes the limitations of traditional methods for tunnel portal stability analysis.
• Its clear discrimination method (variational value sign) and comprehensive indicator offer a reliable new reference.
• The variational criterion provides a more efficient and accurate approach for assessing tunnel portal safety.