Limitation of convergence-confinement method on three-dimensional tunnelling effect.

Area of Science:

• Geotechnical Engineering
• Tunneling Engineering
• Rock Mechanics

Background:

• The convergence-confinement method (CCM) is a common tool for tunnel support design.
• CCM simplifies 3D tunnel advance problems into 2D plane strain analyses.
• Limitations arise from ignoring three-dimensionality, leading to deviations from actual behavior.

Purpose of the Study:

• To investigate the limitations of CCM in reflecting 3D tunneling effects.
• To compare CCM results with 3D numerical modeling for deformation, support pressure, and liner loads.
• To understand the reasons behind discrepancies between CCM and 3D analyses.

Main Methods:

• Comparison of CCM and 3D numerical modeling results.
• Analysis of tunnel deformation, support pressure, and liner loads.
• Evaluation across various geological conditions in a typical tunnel case.

Main Results:

• CCM shows deviations from 3D numerical modeling in rock deformation and support pressure.
• The study explains the reasons for these differences, highlighting the impact of 3D effects.
• Acceptable use of CCM is dependent on rock mass strength and tunnel depth.

Conclusions:

• CCM's 2D simplification introduces inaccuracies in 3D tunnel scenarios.
• A rigorous 3D approach is necessary for certain geological conditions and tunnel depths.
• Guidelines are provided to determine when CCM is appropriate versus when 3D analysis is required.