Study on mechanical properties of coal before and after flooding considering bedding direction

Abstract

The weak bedding plane and the water-softening coal will lead to the decrease in mechanical properties, which has an important influence on the stability of underground reservoirs and the prevention and control of water inrush accidents in coal mine. To study the comprehensive influence of bedding and soaking on the mechanical properties of coal, the uniaxial compression deformation and failure characteristics of coal under different soaking conditions were analyzed through a non-destructive soaking test and uniaxial compression test and based on the Digital image correlation method (DIC). The mechanical property parameters and surface strain field information of axial parallel and vertical bedded coal samples in the natural state, natural water absorption and forced water absorption were obtained. The results shown that the water absorption characteristics of coal shown obvious stratification differences, and the mechanical properties were affected by the combined effects of stratification and soaking. The specific results were as follows, ① Capillary action led to stronger water adsorption in axial parallel-bedded coal than in axial vertical-bedded coal, and the natural limiting water absorption rate of axial parallel-bedded coal was 2.2 times higher than that of axial vertical-bedded coal. ② The uniaxial compressive strength and elastic modulus of coal were mainly affected by bedding and supplemented by soaking. The failure mode was related to the direction of bedding. The failure mode of axial vertical coal was shear failure, while that of axial parallel coal was split failure. ③ The coal failure was a process of transformation from uniform to non-uniform deformation. After water soaking, the coal appeared strain concentration area earlier, its compaction stage was prolonged, and the elastic deformation stage was shortened. The research results were helpful to further understand the water soaking characteristics, mechanical properties, and rupture evolution of axial parallel and vertical bedded coals, and can be used as a reference for the protection and stability analysis of reserved coal pillars in underground reservoirs.

Keywords

• bedding coal
• water-saturated coal
• uniaxial compression experiments
• 3d-dic technique
• mechanical properties