长期水浸作用下煤样渐进破坏特征及损伤本构模型

Progressive damage characteristics and damage constitutive model of coal samples under long-term immersion

水岩作用是煤岩体弱化的一个重要因素,长期水浸作为水岩作用的一种类型,在采矿工程和井巷工程中广泛存在。通过单轴压缩试验获取长期水浸过程中煤样的渐进破坏特征,建立力学参数与饱和度和浸水时间之间的关系,并分析煤样宏观裂隙扩展特征。结果表明,煤样的浸泡过程可分为非饱和浸泡和长期(饱和)浸泡2个阶段。在非饱和浸泡阶段和长期浸泡阶段,煤样的峰值应力分别降低46.3%和34.5%,且符合指数下降的趋势。在长期水浸的过程中,煤样加载后产生宏观裂缝的数量由干燥状态的6~8条逐渐减少至浸泡360 d的2~3条,且破坏形式由拉伸和剪切复合破坏向单一剪切破坏转变。根据煤样初始压密特征以及临界破坏强度特征,采用连续损伤力学和统计损伤理论提出一种描述煤样在长期水浸作用下整个变形过程的损伤本构模型。基于此模型可以发现随着浸水时间的增加,初始损伤量由干燥煤样的0逐渐增加至浸泡360 d煤样的0.773。此外,通过引入均方根误差RMSE和决定系数R^(2)来评估模型曲线与试验数据之间误差和拟合度,发现改进后模型的理论曲线与试验数据吻合度最高。改进后模型的RMSE最大值和R^(2)最小值分别为1.81和0.76,均优于已有文献提出的模型。

Water-rock interaction is an essential factor in the weakening of coal rock masses.Long-term immersion as a type of water-rock interaction is widespread in mining engineering and shaft engineering.The progressive damage characterization of coal samples during long-term immersion is obtained by a uniaxial compression experiment.The relationship between mechanical parameters and saturation and immersion time is established,and the macroscopic fracture extension characteristic of coal samples are analyzed.The results show that the soaking process of coal samples can be divided into two stages:unsaturated immersion and long-term(saturated)immersion.The peak stress in coal samples decreases by 46.3%and 34.5%in the unsaturated stage and long-term immersion stage,respectively,which conforms to the exponentially decreasing trend.During long-term immersion,the number of macroscopic cracks produced in coal samples after loading gradually decreases from 6–8 in a dry to 2–3 in a 360 d soaked.The damage mode changes from combined tensile and shear damage for unsaturated coal samples to single shear damage for 360 d soaked coal samples.Based on initial compression characteristics and critical damage strength characteristics in a coal sample,a damage constitutive model describing the whole deformation process of a coal sample under long-term immersion is proposed using continuous damage mechanics and statistical damage theory.According to this model,it can be found that the initial damage increases gradually from 0 in a dry sample to 0.773 for a soaked 360 d sample with the increase of soaking time.In addition,the error and fit between model curves and the experimental data are evaluated by introducing the root mean square error(RMSE)and the coefficient of determination(R^(2)).The theoretical curves of the improved model are found to be the highest matching with the experimental data.The maximum value of RMSE and the minimum value of R^(2) for the improved model are 1.81 and 0.76,respectively,which are better than the models proposed in existing papers.