Study on energy evolution characteristics and unloading degradation failure mechanism of deep coal seam floor rock mass

In order to study the energy characteristics and unloading degradation mechanism of floor rock mass during deep coal mining, rock mechanics tests under different confining pressure unloading rates were carried out. The characteristics of rock damage fracture energy and elastic modulus at different unloading stages were analyzed by comprehensive theoretical analysis and laboratory tests. According to the analysis results, the deformation and failure of rock in the process of confining pressure unloading can be divided into three stages: from the starting point of confining pressure unloading to instability failure, from instability failure to accelerated failure, and into accelerated failure. Under the same axial pressure, different confining pressure unloading rates had little effect on the degradation degree of rock elastic modulus from the starting point of confining pressure unloading to instability failure stage and from instability failure to accelerated failure stage. From the starting point of confining pressure unloading to instability failure stage, the energy consumption of damage and fracture was less, but the rock elastic modulus obviously deteriorated. In the stage of instability failure to accelerated failure, the degradation degree of elastic modulus was slower than that from the starting point of confining pressure unloading to instability failure stage, but the energy consumption of damage and fracture showed an increasing trend. When the rock entered the accelerated failure stage, the energy consumption of damage and fracture increased with the increase of confining pressure unloading rate, and the macroscopic penetrating cracks of coal seam floor was easy to form, which increased the risk of water inrush in deep mining. © 2023 China University of Mining and Technology. All rights reserved.