Unstable behavior of segmental ring under various pressures and its discrete element simulation

Area of Science:

• Geotechnical Engineering
• Tunneling Engineering
• Mechanical Engineering

Background:

• A fatal TBM tunneling accident in Japan in 2012 was caused by key-segment slippage.
• This slippage led to segment ring collapse, allowing seabed ground and seawater to inundite the tunnel.
• Understanding segment ring stability is crucial for TBM tunneling safety.

Purpose of the Study:

• To investigate the behavior of thin and thick tunnel segments without circumferential joints under pressure.
• To evaluate the impact of lubrication on the contact surfaces between key (K-) and adjacent (B-) segments.
• To analyze the structural integrity of segment rings during TBM tunneling operations.

Main Methods:

• Small-scale physical model tests were conducted to simulate TBM segment behavior.
• Pressures were applied to the exterior of segment rings, and strains were measured.
• Discrete element simulations were performed to analyze segment interactions, with and without lubrication.

Main Results:

• Physical models and simulations provided insights into segment ring deformation under various pressures.
• The study evaluated the influence of lubrication on the contact surfaces between key and adjacent segments.
• Strain measurements helped assess potential damage and failure modes of the segment rings.

Conclusions:

• The findings contribute to understanding the mechanical behavior of TBM segment rings under stress.
• This research can inform improved TBM design and construction practices to prevent accidents.
• Preventing key-segment slippage is vital for ensuring the safety and stability of sub-seabed tunnels.