An Experimental Research on Surrounding Rock Unloading during Solid Coal Roadway Excavation

Abstract

In order to further explore the deformation and failure essence of the deep coal body, based on the characteristics of surrounding rock stress adjustment before and after solid coal roadway excavation, an experiment of unloading confining pressure and loading axial pressure of the coal body was designed and conducted in this study. Based on test results, the failure mechanics and energy characteristics of the coal body were analyzed through experiments. Rapid unloading is considered a key factor contributing to lateral deformation and expansion failure, which exacerbates the deterioration of coal body and reduces the deformation energy storage capacity of coal. On the other hand, the larger loading rate tends to shorten the accumulation time of microcracks and cause damage to the coal body, resulting in strengthening the coal body and improving energy storage. Under the circumstance that the coal body is destroyed, the conversion rates of the internal deformation energy and dissipated energy are more significantly affected by unloading rate. The increasing unloading rate and rapid decreases in the conversion rate of deformation energy make the coal body more vulnerable to damage. Under the same stress conditions, the excavation unloading is more likely to deform, destroy, or even throw the coal than the experiment unloading. In order to reduce or avoid the occurrence of deep roadway excavation accidents, the understanding of the excavation unloading including possible influencing factors and the monitoring of the surrounding rock stress and energy during the excavation disturbance should be strengthened. It can be used as the basis for studying the mechanism of deformation and failure of coal and rock and dynamic disasters in deep mines, as well as the prediction, early warning, prevention, and control of related dynamic disasters.

Multifactor analysis of roof deformation and reasonable determination of the unsupported distance of a coal roadway heading face based on response surface method

“…Yi et al 22 analyzed the laws of strain energy transfer and dissipation in deep roadways surrounding rock when considering the objective strain softening and dilatancy behavior, then analyzed the large deformation mechanism of surrounding rock. Guo et al 23 analyzed the failure mechanics and energy characteristics of coal mass on the basis of confining pressure unloading and axial pressure loading experiments, and showed that rapid unloading was the key factor leading to lateral deformation and expansion failure of coal mass. Zhang et al [24][25][26] based on the operating vibration signal acquisition system, studied the basic characteristics of microseismic events in the heading face, including the occurrence location, main frequency range, maximum amplitude range, event duration, and the relationship between stress and deformation in the heading face.…”

A Study on the Effects of Loading Axial Pressure Rate on Coal Mechanical Properties and Energy Evolution Law

“…The relevant mechanical properties of engineering coal and rock mass serve as the foundation for the design, construction, and related disaster prevention of geotechnical and underground engineering and have always been favored by the scientific and technological workers all the time. In recent years, some studies have shown that in practical engineering, especially underground or mining engineering, the stress characteristics of excavation surrounding rock are more in line with the stress path of unloading confining pressure and axial loading [3][4][5]. Zhao [6] analyzed the rock mechanic principle of major deep engineering in details and discussed eight unsolved century-old problems of rock mechanics.…”

An Investigation on the Impact of Unloading Rate on Coal Mechanical Properties and Energy Evolution Law

“…Some in depth research revealed that the mechanical parameters of the rock mass under loading and unloading conditions were significantly different [3]. In addition, the actual excavation process included in deep engineering projects (such as the roadway excavation [4]) shares more similarities with the unloading path [5]. Compared to the loading path, the measured mechanical parameters of the unloading path tend to be more accurate [6].…”

“…Hou et al [22,23] utilized cement mortar to process roadway surrounding rock specimens, and conducted a series of excavation and unloading model tests. Some studies also indicated that the stress adjustment process of surrounding rock in roadway excavation can be simplified as the stress path of unloading confining pressure [4,5], indicating that the initial stress, unloading confining pressure rate, and loading axial pressure speed, etc., can directly affect the damage and destruction of surrounding rock. However, few relevant studies have been conducted on the mechanical tests of coal and rock mass under the aforementioned stress path conditions, its energy evolution, and practical guidance, in combination with actual engineering.…”