Three-Dimensional Discrete Element Analysis on Tunnel Face Instability in Cobbles Using Ellipsoidal Particles.

Area of Science:

• Geotechnical Engineering
• Computational Mechanics

Background:

• Soil disturbance is a primary concern in shield tunneling.
• Understanding micro-scale soil behavior is crucial for predicting tunnel face stability, especially in complex strata like sandy cobbles.

Purpose of the Study:

• To investigate the micro-scale responses of soils during shield tunnel excavation in sandy-cobble strata.
• To analyze the mechanisms of tunnel face instability in cobbles using advanced simulation techniques.

Main Methods:

• Discrete Element Method (DEM) simulations using the paraEllip3d code, modeling soils as assemblies of ellipsoids.
• Calibration of micro-parameters through triaxial tests on sampled cobble materials and corresponding DEM simulations.
• 1g model tests and DEM simulations to study tunnel face instability during shield tunneling in cobbles.

Main Results:

• Detailed analysis of micro-scale cobble responses, including stress-strain relationships, contact distribution, and force chain evolution.
• Validation of DEM simulation parameters through comparison with experimental triaxial tests.
• Investigation into the mechanisms governing tunnel face instability in cobble-rich soil.

Conclusions:

• DEM simulations provide valuable insights into the micro-scale behavior of soils during shield tunneling.
• The study elucidates the mechanisms of tunnel face instability in sandy-cobble strata.
• Findings contribute to improved design and safety in shield tunneling operations within challenging geological conditions.