Coal rock water immersion softening is common in coal geology, and it is of great significance to effectively control and utilize the process of water immersion softening and fracturing of coal. In this paper, the progressive failure and softening characteristics of coal samples under localized or full water immersion conditions were determined based on the stress-strain and acoustic emission (AE) response under uniaxial compression, and the obtained characteristics were compared to the properties of the as-received coal as a control. The uniaxial compressive strength, axial stiffness, and softening coefficient of the water-immersed coal samples were reduced compared to those of the control, and the softening degree increased with increasing degree of water immersion. Further, the stress threshold values for crack initiation and crack damage and their ratios to the peak stress decreased with increasing softening degree. The crack damage (CD) point marked the beginning of the unstable propagation of visible fractures and the intense evolution of tensile/shear cracks, accompanied by a rapid increase in the AE counts, regardless of whether the coal had been water-immersed or not. For quantitative characterization and identification of softening characteristics, a new comprehensive index and its softening coefficient are proposed considering the stress threshold and volumetric strain at the CD point, and it is applied to the step-by-step fracturing mechanism of softened coal by hydraulic fracturing. The effective utilization of coal softening and fracturing can avoid the harsh conditions imposed by high-pressure water injection in hydraulic fracturing, which alleviate the dynamic disaster of coal and rock to a certain extent.

煤岩水浸软化在煤炭地质中普遍存在，有效控制和利用煤的水浸软化和压裂过程具有重要意义。本文基于单轴压缩下的应力-应变和声发射（AE）响应，确定了煤样在局部或全浸水条件下的渐进破坏和软化特性，并将所得特性与煤样的特性进行了比较。原样煤作为对照。与对照相比，水浸煤样的单轴抗压强度、轴向刚度和软化系数均降低，且软化程度随着水浸程度的增加而增加。更远，裂纹萌生和裂纹损伤的应力阈值及其与峰值应力的比值随着软化程度的增加而降低。裂纹损伤 (CD) 点标志着可见裂纹的不稳定扩展和拉伸/剪切裂纹的剧烈演变的开始，伴随着 AE 计数的快速增加，无论煤是否浸水。为定量表征和识别软化特性，提出了考虑CD点应力阈值和体积应变的新综合指标及其软化系数，并将其应用于水力压裂软化煤的逐级压裂机理。 .