Key Takeaways & Executive Findings
- •• Increasing moisture content reduces peak stress and crack initiation stress by 15.28%–21.11% and 17.64%–23.04%, respectively, while increasing peak and crack initiation strains by 19.85%–44.53% and 19.15%–41.94%. • Pre-cracked rocks under different moisture contents predominantly exhibit tensile failure, but higher water content increases the proportion of shear cracks. • Higher water content decreases acoustic emission events and dissipative energy, while significantly increasing charge signals, due to water's lubrication reducing crack surface friction. • The study integrates DSCM, AE, and EMR to reveal failure precursors and damage mechanisms in pre-cracked rocks under graded cyclic loading, aiding in rock mass stability assessment.
Abstract
It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass. Based on digital speckle correlation (DSCM), acoustic emission (AE) and electromagnetic radiation (EMR), uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry, natural and saturated water content, to explore the fracture propagation, failure precursor characteristics and damage response mechanism under the influence of water content effect. The results show that with the increase of water content, the peak stress and crack initiation stress decrease gradually, and the decreases are 15.28%–21.11% and 17.64%–23.04%, respectively. The peak strain and crack initiation strain increase gradually, and the increases are 19.85%–44.53% and 19.15%–41.94%, respectively. The precracked rock with different water content is mainly characterized by tensile failure at different loading stages. However, with the increase of water content, the proportion of shear cracks gradually increases, while acoustic emission events gradually decrease, the dissipative energy and energy storage limits of the rock under peak load gradually decrease, and the charge signal increases significantly, which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.
1. Introduction
In the process of mining and gas extraction, coal and rocks are subject to long-term cyclic disturbance of various mining stresses in addition to ground stress, and can be simplified as the cyclic loading and unloading process of coal and rocks [1–8]. The load increases with the increase of burial depth, leading to the gradual deterioration of the bearing mechanical properties of coal and rocks under disturbance [9–11]. Due to long-term crustal movement and sedimentation, underground coal and rocks generally have a large number of weakly structural planes such as cracks inside. The existence of primary cracks can reduce the fracture strength of coal and rocks to varying degrees, and cracks that propagate and penetrate become key locations for stress release and concentration, which have a significant impact on engineering stability. Therefore, studying the failure mechanism and crack evolution law of rocks under cyclic loading and unloading is helpful for achieving safe mining and early warning of rock mass disasters [12–14].
To analyze the bearing characteristics of rocks under cyclic loading and unloading, Zhang et al. [15,16] conducted cyclic loading and unloading tests on pre-cracked rocks and proposed that irreversible deformation increasing with the number of cycles is the fundamental cause of rock fatigue damage. Li et al. [17] conducted cyclic loading and unloading tests with equal amplitudes on pre-cracked limestone, and found that compared to the results of static loading tests, the difference between the peak strain and initial failure strain of the rock was significantly reduced. Liu at al. [18] investigated the influence of crack number on the elastic modulus of rocks under cyclic loading and unloading, and proposed that the elastic modulus gradually strengthens with increasing cycles, and the first cycle has the highest strengthening amplitude on the elastic modulus. Zhang et al. [19] investigated the failure characteristics of pre-cracked rocks under cyclic loading and unloading, found that fatigue cracks first propagate at the crack edge where stress concentration occurs. Li et al. [20] conducted numerical simulations of cyclic loading and unloading tests on pre-cracked marble, found that there is an extension of the fracture process zone at the front of the cracks.
Loading authentic research manuscript (Pages 1–5)...
ZHANG Wei, ZHANG Dongxiao, GUO Weiyao, ZHANG Baoliang (2024). Experimental study on failure precursory characteristics and moisture content effect of pre-cracked rocks under graded cyclic loading and unloading. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2024.12.014
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the main objective of this study?
The main objective is to analyze the damage evolution process of surrounding rock under different water content conditions, using digital speckle correlation, acoustic emission, and electromagnetic radiation to explore fracture propagation, failure precursor characteristics, and damage response mechanisms in pre-cracked sandstones under graded cyclic loading and unloading.
How does moisture content affect the mechanical properties of pre-cracked rocks?
Increasing moisture content reduces peak stress and crack initiation stress by 15.28%–21.11% and 17.64%–23.04%, respectively, while increasing peak strain and crack initiation strain by 19.85%–44.53% and 19.15%–41.94%, respectively.
What failure modes are observed in pre-cracked rocks under different moisture contents?
Pre-cracked rocks under different moisture contents predominantly exhibit tensile failure at various loading stages. However, with increasing water content, the proportion of shear cracks gradually increases.
What is the role of water in the damage process?
Water has a lubrication effect that reduces the friction coefficient between crack surfaces, leading to decreased acoustic emission events and dissipative energy, while significantly increasing charge signals.
What techniques were used to monitor failure precursors?
The study employed digital speckle correlation (DSCM), acoustic emission (AE), and electromagnetic radiation (EMR) to monitor and analyze failure precursors and damage evolution in real-time.
Related Technical Papers & Translations
A Novel Approach for Enhanced Brain Tumor Segmentation Using Multimodal MRI and Deep Learning
Brain tumor segmentation from multimodal MRI is crucial for diagnosis and treatment planning. In this study, we propose a novel deep learning framework that integrates structural and functional imaging modalities to improve segmentation accuracy. Our method employs a multi-scale attention mechanism and a hybrid loss function to handle class imbalance and boundary ambiguity. Evaluated on the BraTS benchmark, our approach achieves state-of-the-art performance, with Dice scores of 0.91, 0.87, and 0.84 for whole tumor, core, and enhancing tumor, respectively. Furthermore, we demonstrate the generalizability of our model across different scanners and protocols. Our findings suggest that the proposed method can significantly aid clinical decision-making and surgical planning.
Investigation of coupled acoustic and electrical responses and early warning approaches during re-loading of damaged coal
Initial damage from engineering disturbances in deep coal mining degrades mechanical properties and heightens dynamic-hazard risks, challenging conventional monitoring. This study probes the coupled acoustic-electrical responses of initially damaged coal under reloading and develops a multi-parameter, multi-level dynamic integrated early-warning model. Using a true-triaxial Split Hopkinson Pressure Bar (SHPB) system, we prepared specimens with graded damage by varying static deviatoric stresses and dynamic impacts. Uniaxial compression reloading was conducted with synchronous acoustic emission (AE) and resistivity monitoring. Joint time-domain responses of force, acoustics, and electricity delineated distinct loading stages. Time-frequency features were extracted via Fourier and wavelet transforms; crack architecture was quantified by 3D AE localization and fractal-dimension analysis. Initial damage markedly reduced load-bearing capacity. Resistivity decreased sharply with increasing deviatoric stress, while cumulative AE counts increased strongly. The AE spectrum evolved from bimodal to broadband with low- and high-frequency enhancement. The resistivity spectrum showed progressive bandwidth broadening, energy amplification, and high-frequency advancement. The AE spatial fractal dimension rose significantly during compaction. An integrated warning system combining multiscale entropy fusion, Temporal Convolutional Network (TCN)-Transformer forecasting, recurrence-network analysis, and a Bayesian framework yielded a 28.4 s lead time, offering a theoretical basis and technical pathway for intelligent prevention of dynamic hazards.
Influence of aggregate particle size on fracture behavior and energy evolution of cemented rockfill in the post-peak stage
Cemented rockfill (CRF) combines structural support with sustainable reuse of coal-derived solid waste. This study integrates digital image correlation, acoustic emission monitoring, and finite–discrete element simulations to investigate mechanical behavior, fracture development, and energy evolution of CRF containing 54% aggregate content with three grain-size distributions (5–10, 10–20, and 20–30 mm). Results indicate finer aggregates raise compressive strength and elastic modulus, and increase post-peak softening and residual stiffness. Fracture patterns transition from dominantly unidirectional failure in coarse specimens to pronounced X-shaped conjugate shear in fine specimens, with cracks initiating at boundaries and propagating inward. The proportion of failed joints at comparable strains decreases markedly with finer gradation, reflecting a more homogeneous crack network that enhances post-peak load retention and produces frequent minor stress fluctuations. Energy analyses reveal a coarse > medium > fine ordering in cumulative dissipation; however, finer aggregates delay rapid kinetic and dissipative energy release, promoting slower energy redistribution and improved load resistance. These findings quantify how aggregate gradation controls deformational mechanisms, crack topology, and energy partitioning, and provide design guidance for optimizing aggregate size and cementitious composition to enhance ductility, energy absorption, and structural reliability of CRF in underground engineering.