Tunnel failure mechanism during loading and unloading processes through physical model testing and DEM simulation

Area of Science:

• Geotechnical Engineering
• Rock Mechanics
• Computational Geomechanics

Background:

• Geo-materials exhibit anisotropic mechanical behavior under varying stress paths.
• Tunnel excavation involves complex loading and unloading cycles, altering stress states around the opening.

Purpose of the Study:

• To investigate fracture propagation patterns and microscopic stress distributions in rock masses surrounding tunnels.
• To compare the effects of loading and unloading stress paths on rock mass integrity and failure mechanisms.

Main Methods:

• Comparative analysis of physical model testing under different stress paths.
• Particle Flow Code 2D (PFC^2D) simulations to model rock mass behavior.
• Examination of tensile strain development, stress, and force chain distributions.

Main Results:

• Distinct differences in tensile strain extent and development were observed between loading and unloading conditions.
• Failure pattern transitions were systematically examined, revealing overall stability and rock mass integrity changes.
• Under unloading, V-shaped extruded sidewall collapse occurred due to coupled shear and vertical tensile failure.

Conclusions:

• The study highlights the critical influence of stress path variations on tunnel-surrounding rock mass behavior.
• Understanding these complex mechanical responses is crucial for ensuring tunnel stability and safe excavation design.
• PFC^2D simulations effectively complement physical testing for detailed analysis of failure mechanisms.