United States Department of Transportation
ROSA P serves as an archival repository of USDOT-published products including scientific findings, journal articles, guidelines, recommendations, or other information authored or co-authored by USDOT or funded partners.
As a repository, ROSA P retains documents in their original published format to ensure public access to scientific information.
i
Experimental Investigation of Rockburst Phenomenon in Tunnels Using a True-triaxial Apparatus
-
2024-10-01
[PDF-20.03 MB]
Details:
-
Creators:
-
Corporate Creators:
-
Corporate Contributors:
-
Subject/TRT Terms:
-
Publication/ Report Number:
-
Resource Type:
-
Geographical Coverage:
-
Corporate Publisher:
-
Abstract:Brittle instabilities during tunnel excavation can cause severe consequences, including spalling, rock bursts, and even tunnel collapse. These detached rock fragments compromise tunnel stability and pose significant safety risks to personnel and equipment, often halting operations. Although in-situ studies and lab tests over past decades have advanced understanding of brittle failure, the mechanisms behind the progression and extent of damage remain insufficiently understood, limiting effective prediction and prevention strategies. This project aims to enhance the understanding of brittle instabilities in tunnels through laboratory experiments. The study involves (1) developing an analog brittle rock model, (2) conducting tunnel model tests using a true-triaxial loading cell, a miniature tunnel boring machine (TBM), and acoustic emission (AE) monitoring, and (3) proposing improved analytical and predictive methods for brittle failure. The analog rock was designed to replicate brittle sedimentary rock behavior while maintaining low uniaxial compressive strength (UCS). This allowed for larger specimen sizes and compatibility with low-capacity loading equipment, making it easier to observe progressive tunnel failure. Using the true-triaxial setup and mock TBM enabled realistic simulations of tunneling, capturing the effects of stress unloading and face support. Detailed post-mortem analysis revealed damage mechanisms such as surficial spalling and V-shaped notches caused by progressive shear fracturing, reflecting a brittle-to-ductile transition. AE sensors monitored microcracking in real-time, identifying early indicators of brittle failure. The study also introduced triaxial extension (TE) tests to improve predictions of spalling under more representative stress conditions compared to traditional triaxial compression (TC) tests. TE tests better captured damage characteristics such as entry angles and fracture depth. In tunnel models, steeply angled thin spalling suggested shear-driven fractures rather than purely extensional ones, with fracture surfaces likely forming from shear-induced dilation and friction mobilization. A novel aspect of the research is the use of quadratic Bézier curves to track fracturing progression based on damage and breakout width. This method offers a more accurate depiction of tunnel damage under anisotropic stress than traditional models relying solely on friction angle and logarithmic spirals. In summary, this project advances the understanding of brittle failure in tunnel excavation. The experimental methods and models developed provide practical tools for mitigating spalling and rockburst risks, contributing to safer and more reliable designs in brittle rock environments.
-
Format:
-
Funding:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type:
