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Field Monitoring Study on Structural Mechanical Behavior of Large-Deformation Tunnels Supported by Energy-Absorbing bolts

Large-Deformation,Energy-Absorbing bolts,Field test

In soft rock tunnels experiencing large deformations, conventional bolt support often leads to phenomena such as bolt fracture, concrete lining cracking, and steel arch distortion. In contrast, energy-absorbing bolts mitigate these issues by releasing the energy stored within the surrounding rock mass.To investigate the structural mechanical behavior of tunnels supported by energy-absorbing bolts, this study implemented a field monitoring program at the Longriba No. 3 Tunnel. Test sections employing energy-absorbing bolts and control sections using conventional bolts were established and monitored.

The findings indicate:(1) Energy-absorbing bolts significantly reduced surrounding rock deformation and structural loading, effectively controlling plastic zone development. Compared to the control section, deformation in the test section decreased by approximately 30%, rock-contact pressure and stress on the arch ribs decreased by about 25%, and bolt axial force decreased by approximately 25%.(2) Energy-absorbing bolts altered the load progression and pattern of the support structure:Early stage (0–20 d):Rock-contact pressure and arch rib stress increased over a longer duration in the test section (50% longer) compared to the control section.Mid-stage (20–40 d):The growth rate in the test section decelerated first. In contrast, the control section exhibited an initial acceleration followed by gradual deceleration.Late stage (>40 d):Loads on all support structures in both sections stabilized, but the loads in the test section remained lower.(3) Energy-absorbing bolts effectively reduced the "asymmetric phenomenon" in rock-contact pressure and arch rib stress.The rock-contact pressure asymmetry coefficient at the sidewalls decreased from 0.461 to 0.334 (a decrease of 37%).The rock-contact pressure asymmetry coefficient at the haunches decreased from 0.164 to 0.102 (a decrease of 28%).The arch rib stress asymmetry coefficient at the sidewalls decreased from 0.394 to 0.201 (a reduction of 49%).The arch rib stress asymmetry coefficient at the haunches decreased from 0.201 to 0.147 (a reduction of 26.9%).The research results deepen the understanding of the mechanical behavior of tunnel structure supported by energy-releasing bolts.





Dear Editors and Reviewers:

I appreciate the opportunity to revise my abstract.

Comment 1: What specific types of soft rock areencompassed by the term "large deformation of soft rock"? ls itexpansive, creep-type, or shear-yielding soft rock?

Respouse 1: I would like to express my sincere gratitude to the reviewer for your insightful comments and valuable feedback. The word soft rock is deleted, and the experimental geological lithology is sandy slate, and there is no soft rock. Soft rock geological environment exists in other miles of this tunnel.

Comment 2: The monitoring solely captures the "stabilization" phasewithin the 0-40 day period; however, the long-term deformation (creepof soft rock formations may persist for months or even years, potentiallysubjecting the support structures to renewed loading. Supplementaryclarification on whether "stability" constitutes pseudo-stability?

Respouse 2: I sincerely appreciate the valuable comment. On-site monitoring was carried out for 70 days, and it began to stabilize on the 40th day, but it was not stable. The wording was inappropriate, and I have corrected it.