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An Integrated FDM–GA Framework for Automated Back Analysis in Tunneling–Part II: Case Study and the Influence of Stress Relaxation Parameters

Document Type : Original Research Paper

Authors

1 Mining Engineering Faculty, Sahand University of Technology, Tabriz, Iran.

2 Lead Associate, Delve Underground, Walnut Creek, CA, USA.

10.22044/jme.2026.17275.3422

Abstract

In the companion Part I paper, an integrated Finite Difference Method–Genetic Algorithm (FDM–GA) framework was developed for automated tunnel back analysis, coupling numerical simulation with evolutionary optimization to estimate geotechnical parameters from field monitoring data. Part II demonstrates the application and validation of this framework through the back analysis of the Pardis Highway Tunnel, excavated within the Hezar Darreh conglomerate formation in northern Tehran, Iran. Three-point convergence measurements from 24 monitoring stations were processed to derive representative reference displacements for calibration. Thirty independent FDM–GA optimization runs were performed to estimate the ground parameters, yielding narrow calibrated ranges for cohesion (c), friction angle (φ), Young's modulus (E), and the coefficient of lateral earth pressure at rest (K0). A representative engineering parameter set was identified by integrating optimization results with inter-parameter correlations and geotechnical evidence from comparable tunnel projects. Unlike conventional tunnel back analysis studies that primarily emphasize parameter optimization, the proposed framework integrates optimization with geological interpretation to identify representative engineering parameter sets. It also systematically evaluates how stress relaxation assumptions influence parameter calibration and the engineering interpretation of calibrated solutions. Recalculated Ground Reaction Curve (GRC) and Longitudinal Displacement Profile (LDP) showed that relatively small variations in stress relaxation assumptions significantly affect predicted convergence and calibrated geotechnical parameters. The results demonstrate that reliable estimation of pre-support deformation and stress release is essential for realistic tunnel back analysis and confirm that the integrated FDM–GA framework provides a robust, repeatable tool for geotechnical parameter calibration in NATM tunnel engineering.

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References
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Journal of Mining and Environment
Volume 17, Issue 5
July and August 2026
Pages 1691-1713
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