Evaluating construction parameters of HB and CD methods for super large section tunnel: a case study.

Area of Science:

• Civil Engineering
• Geotechnical Engineering
• Tunneling Engineering

Background:

• Traditional double sidewall guide pit and center cross diagram (CRD) methods for large tunnels in water-rich fault zones are costly and time-consuming.
• Alternative methods like top heading and benching (HB) and center diaphragm (CD) offer potential for shorter construction periods and reduced expenses.

Purpose of the Study:

• To optimize construction parameters for the HB and CD methods, ensuring surrounding rock stability and tunnel safety.
• To investigate the impact of varying step heights on tunnel vault settlement, surrounding rock stress, and initial support performance using numerical simulations.

Main Methods:

• Numerical simulation of tunnel excavation using HB and CD methods at the Tongzi Tunnel.
• Analysis of tunnel vault settlement, surrounding rock stress, initial support axial force, bending moment, and safety factor under different step height scenarios.

Main Results:

• Increasing upper step height in HB and CD methods leads to greater vault settlement, increased peripheral convergence, and reduced initial support safety factor.
• An increased plastic zone in the surrounding rock was observed at 30m from the target face with larger step heights.
• Optimized step height ratios were determined for both HB (0.45H, 0.35H, 0.2H for upper, middle, lower) and CD (0.5H, 0.5H for upper and lower) methods.

Conclusions:

• The study provides optimized step height configurations for HB and CD methods to enhance safety and stability in large-section tunnels.
• The findings contribute to more efficient and cost-effective tunnel construction in challenging geological conditions.