Abstract
As shallow resources are exhausted, deep resources are gradually being exploited; consequently, mining disasters and accidents have increased significantly over time. During mining, a deep rock mass experiences complex mining‐induced stress evolution, damage accumulation, and deformation failure processes, and the mechanical and acoustic properties of the rock constantly change. To better understand the variation in the mechanical and acoustic properties of rock under loading and unloading conditions, uniaxial loading‐unloading experiments with real‐time ultrasonic P‐wave velocity monitoring were conducted on sandstone specimens drilled from a coal seam roof. The test results show that the axial stress level is directly related to the P‐wave velocity. A logarithmic relationship exists between the ultrasonic P‐wave velocity and stress in the tested sandstones. The wave velocity increase caused by the unit axial pressure increase is significantly lower than that at the initial loading stage after entering the higher stress level. The energy evolution of sandstone during loading and unloading is closely related to the stress loading history and reflects the damage accumulation in the rock. Under elastic loading, the energy accumulation is mainly reflected by an increase in elastic energy, and less energy is dissipated during the elastic loading period. Stress unloading causes high energy dissipation, resulting in irreversible strain and damage accumulation, which provides a good basis for using ultrasonic testing to preliminarily judge the failure of a specific rock and formulate corresponding engineering measures.
Highlights
Coal is the major energy source in China, and coal mining practices have been accelerating due to the rapid decline in shallow coal resources, resulting in a significant increase in coal mine disasters and accidents
Deep rock masses with significant stress sensitivity have experienced complex mining stress evolutions during the mining process and disasters, resulting in damage accumulation and deformation failure [1, 2]. e mechanical and acoustic properties of these rock masses constantly change, which undoubtedly increases the difficulty of coal mine disaster prevention and control
In the Advances in Materials Science and Engineering field of coal mining, an accurate understanding of the acoustic characteristics of a rock under loading is the basis of using ultrasonic testing technology to detect the deterioration degree and mechanical properties of rocks [7, 8]. e study of the acoustic characteristics of rock can help to further develop the practical application of ultrasonic testing technology to solve complex rock mechanical problems in mining
Summary
As shallow resources are exhausted, deep resources are gradually being exploited; mining disasters and accidents have increased significantly over time. A deep rock mass experiences complex mining-induced stress evolution, damage accumulation, and deformation failure processes, and the mechanical and acoustic properties of the rock constantly change. To better understand the variation in the mechanical and acoustic properties of rock under loading and unloading conditions, uniaxial loading-unloading experiments with real-time ultrasonic P-wave velocity monitoring were conducted on sandstone specimens drilled from a coal seam roof. E test results show that the axial stress level is directly related to the P-wave velocity. E energy evolution of sandstone during loading and unloading is closely related to the stress loading history and reflects the damage accumulation in the rock. Stress unloading causes high energy dissipation, resulting in irreversible strain and damage accumulation, which provides a good basis for using ultrasonic testing to preliminarily judge the failure of a specific rock and formulate corresponding engineering measures
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