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Experimental Study on Shear Behavior of Rock Composite Material under Normal Unloading Conditions
Bo Liu1, Yifan Chen1, Hang Lin1
1School of Resources and Safety Engineering, Central South University, Changsha 410083, China.
Materials (Basel, Switzerland)
|February 11, 2023
Summary
Rock joint stability is crucial for excavation safety. This study reveals how decreasing normal stress impacts joint strength and proposes a new method to predict instability using deformation energy evolution.
Area of Science:
- Geotechnical Engineering
- Rock Mechanics
- Composite Materials
Background:
- Rock mass stability is often governed by joints, which are critical in composite materials.
- Excavation processes can lead to decreased normal stress on joints, reducing shear strength and potentially causing rock mass failure.
- Existing research primarily examines joint behavior under constant normal stress, neglecting the effects of normal stress unloading.
Purpose of the Study:
- To investigate the strength characteristics of rock joints under normal stress unloading conditions.
- To analyze the deformation and acoustic emission (AE) behavior of joints during normal stress unloading.
- To propose a novel method for predicting joint instability during normal unloading based on energy evolution.
Main Methods:
- Direct shear tests were conducted on joints with varying roughness, maintaining constant shear stress while decreasing normal stress.
- Digital Image Correlation (DIC) techniques were employed to analyze deformation characteristics.
- Acoustic Emission (AE) monitoring was used to capture micro-fracturing events and analyze AE-counting characteristics.
Main Results:
- The extent of normal stress unloading increased with higher initial normal stress and roughness but decreased with increased initial shear stress.
- Acoustic emission events peaked when normal stress reached the failure point, and the b-value showed increased fluctuation during stable development under unloading.
- Total deformation energy (U0) varied with stress loading and unloading cycles.
Conclusions:
- The study provides insights into the strength characteristics and failure mechanisms of rock joints under normal stress unloading.
- A new method for predicting rock mass instability during normal unloading is proposed, utilizing the abrupt changes in total deformation energy (U0).
- The findings contribute to a better understanding of rock mass behavior in engineering applications involving stress unloading.
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