This standard (Part 1) provides guidelines for the design and construction of large diameter tunnels (>3m) using conventional methods like the New Austrian Tunnelling Method (NATM) or drill-and-blast. It covers aspects from geotechnical investigations and empirical design based on rock mass classification to support systems and construction sequences.
Provides guidelines for the design and construction of large diameter tunnels using conventional methods, including drilling and blasting.
Quick Reference Values
Typical allowable deviation in tunnel alignment±50 mm to ±100 mm
Typical annular gap for backfill grouting150 mm to 250 mm
Typical grout pressure1.5 to 2.0 times the overburden pressure
Minimum thickness of precast concrete segmentsGenerally not less than 150 mm, or D/50 (D=tunnel dia)
Minimum cover for tunneling under structuresOften > 1.5 times the tunnel diameter, project-specific
Key Formulas
H_p = (1.5B + 0.5H_t) — Rock load height in squeezing rock (mild)
P_v = γ * z — Vertical in-situ stress at depth z
t = (P * R) / σ_allow — Required support thickness (simplified membrane theory)
Practical Notes
Selection of the correct TBM type (e.g., Earth Pressure Balance, Slurry Shield, Open Gripper) based on thorough geotechnical investigation is the single most critical factor for project success.
The design of segmental lining is an iterative process involving analysis of ground-structure interaction, handling/erection stresses, and long-term durability requirements.
Continuous monitoring of ground settlement, TBM operational parameters (e.g., face pressure, torque), and lining integrity is essential throughout the construction phase.