Abstract
The stability of coal wall in deep longwall face has always been a research hotspot. In this study, pure vibration signals in the coal wall during the operation of mining machinery were obtained for the first time, and their energy is mainly concentrated in 7–12 Hz. Besides, based on the law of stress wave propagation, with the coal wall of deep longwall taken as the research object, the theory of dynamic damage in coal wall was put forward from the perspective of dynamics. The results show that the loading and unloading waves generated by the mining machinery disturbance will be reflected and transmitted at the interface with different impedances, resulting in the formation of multiple unloading and loading waves and multiple tensile stress zones and stress concentration zones. These stress concentration zones tend to induce tensile stress generation and coal failure. As a result, the coal undergoes zonal failure and spalling. Through the vibration test of coal, it is found that the crack development of the coal sample can be divided into five stages, and the phenomena of zonal failure and spalling occur, which is consistent with the theory. At the same time, the sample that has gone through a large disturbance cannot be further damaged by a small disturbance, which is verified by the damage statistical constitutive model based on the isotropy hypothesis.
Highlights
Mechanized mining technology, which has been widely used in deep mines in China, is considered as a production mode to achieve efficient production and improve recovery rate [1,2,3]. e factors affecting coal wall stability in the working face have been extensively researched on, and these researches mainly focused on the coal seam, the mining height, the roof load, and the mechanical properties of coal and rock [4,5,6]. eoretical modeling on coal wall stability has been carried out by researchers. ese models include the shaft theory [7, 8], the Ritz method [9], and the shear model [10], all of which belong to static analysis
When the dynamic load is superimposed on the working face area and exceeds the ultimate strength of coal, the coal will be damaged, and even sudden disasters like rock burst will occur. e dynamic load stress at the working face mainly includes vibration disturbance caused by mining machinery and coal burst induced by mining
Since the operation of coal mining machinery just generates limited disturbance energy in the working face and affects a small range of area, this study focuses on analyzing the effect of disturbance load on Area A
Summary
Mechanized mining technology, which has been widely used in deep mines in China, is considered as a production mode to achieve efficient production and improve recovery rate [1,2,3]. e factors affecting coal wall stability in the working face have been extensively researched on, and these researches mainly focused on the coal seam, the mining height, the roof load, and the mechanical properties of coal and rock [4,5,6]. eoretical modeling on coal wall stability has been carried out by researchers. ese models include the shaft theory [7, 8], the Ritz method [9], and the shear model [10], all of which belong to static analysis. E dynamic load stress at the working face mainly includes vibration disturbance caused by mining machinery and coal burst induced by mining. E results showed that as the cyclic loading and unloading time went by, the permeability loss, stress sensitivity, and crushing amount of broken coal were gradually reduced. In their researches on vibration-induced failure of coal and rock mass, Litwiniszyn [17] and Pan et el. To investigate the influence of mining machinery disturbance on the coal wall in deep wells and discuss the mechanism of dynamic damage in the coal wall, following work was conducted in the study. The stress evolution law and fracture development process of coal were analyzed by using the damage statistical constitutive model based on the isotropy assumption
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