真三轴加卸载条件下煤样应力能量演化特征与破裂损伤规律

发布时间：2018-08-20 17:47

【摘要】：针对不同地应力异常区中小尺度采掘时加卸载导致的动力灾害问题,基于真三轴采动煤岩体动力显现实验系统,设计了能够实现实时监测的真三轴声发射监测单元,并综合采用实验室实验、理论分析等手段,对真三轴受载下煤样力学性质与失稳破坏特征、声发射规律以及微破裂、波速和时空演化规律进行了系统探究。声发射研究结果表明,真三轴受载煤样振铃计数受载荷水平、个体差异与加载速率影响。在低载荷水平下,由振铃计数代表的煤样损伤较多出现于加载阶段,且数量较少。随着载荷水平的增加,煤样内振铃计数逐渐升高,保压阶段的振铃计数也大幅增加,表明煤样损伤过程逐渐由加载阶段向保压阶段转移。此外,在不同载荷水平下,煤样内声发射事件主要集中于加载初期,而声发射事件总量则随着载荷水平的逐渐增加而具有先上升后下降的趋势。在极高载荷水平下,声发射事件极少并平均分布于整个加载阶段。力学与失稳破坏特征研究结果表明,真三轴中、低载荷受载煤样在各方向均呈现出压缩状态,但随着最大主应力与中间、最小主应力逐渐增加,最小主应力方向与中间主应力方向相继出现扩容现象。在低载荷水平下,煤样内主要以张拉破裂为主,随着载荷水平不断增加,微破裂类型逐渐转变为剪切破裂,同时破裂数量在保压阶段的上升速度有明显增加。在进行单面自由状态的三轴卸荷时,低载荷受载煤样因未达到承载极限,其外观仍保持完整形态且无明显动态破坏发生,而高载荷受载煤样因已达到承载极限而在内部遭受二次损伤,其破坏以煤渣在自由面大量掉落的形式发生。微破裂、波速与能量演化规律研究结果表明,在真三轴加载初期,原生孔隙逐渐闭合与原生致密区的初始受载使此阶段煤样内出现少量的高、低波速区。随着载荷逐渐增加,原生孔隙压实与致密区破裂造成高波速区转移扩展与波速异常区形成。煤样接近破坏时,宏观裂隙的贯通使煤样内出现大面积低波速带,内部大量产生与闭合的裂隙使高波速区、波速异常区迅速变化转移,煤样已处于不稳定状态。在真三轴高载荷保压阶段,由于煤样裂隙的不断压实与内部结构特征的充分破坏,煤样内出现以低波速区不断减小与整体波速提高为代表的持续性损伤。此外,在真三轴加载阶段,煤样内累计破裂释放能量分布较为集中,其位置大致对应高波速区与波速异常区,同时极大值也不断升高。当煤样失稳破坏后,累计破裂释放能量分布逐渐分散并贯穿整个试样,其极大值增速却趋于平缓。
[Abstract]:In order to solve the problem of dynamic disasters caused by loading and unloading in different geostress anomaly areas, a true triaxial acoustic emission monitoring unit is designed based on the real triaxial coal and rock dynamic behavior experimental system. By means of laboratory experiments and theoretical analysis, the mechanical properties and the characteristics of instability, acoustic emission, microfracture, wave velocity and space-time evolution of coal samples under true triaxial loading are studied systematically. The results of acoustic emission study show that the ringing count of true triaxial loaded coal samples is affected by loading level, individual difference and loading rate. At the low load level, the damage of coal samples represented by ringing count appears more in the loading stage and the quantity is less. With the increase of loading level, the ringing count of coal samples increases gradually, and the ringing count of the holding stage increases significantly, which indicates that the damage process of coal samples is gradually transferred from loading stage to holding pressure stage. In addition, under different loading levels, the acoustic emission events in coal samples are mainly concentrated at the initial loading stage, while the total acoustic emission events tend to rise first and then decrease with the increasing of load level. At extremely high load level, acoustic emission events are rarely and evenly distributed throughout the loading stage. The results of mechanical and unstable failure characteristics show that in the true triaxial, the low-load loaded coal samples show a compression state in all directions, but with the maximum principal stress and the middle, the minimum principal stress increases gradually. The minimum principal stress direction and the intermediate principal stress direction are expanded one after another. At the low load level, the tensile fracture is the main factor in the coal sample. With the increasing of the load level, the micro-fracture type gradually changes into shear fracture, and the amount of fracture increases obviously in the pressure keeping stage. When the triaxial unloading is carried out in one side free state, the low-load loaded coal sample does not reach the loading limit, and its appearance remains intact and has no obvious dynamic damage. The high load loaded coal samples suffer secondary damage in the interior because they have reached the loading limit, and the damage occurs in the form of a large amount of coal slag falling off the free surface. The results of microfracture, wave velocity and energy evolution show that at the beginning of true triaxial loading, the primary pores are gradually closed and the initial loading of the primary dense zone leads to a small amount of high and low wave velocity zones in the coal samples at this stage. With the increasing of the load, the primary pore compaction and the fracture of the dense zone result in the transfer and expansion of the high wave velocity zone and the formation of the abnormal wave velocity zone. When coal samples are close to failure, large areas of low wave velocity zones appear in coal samples due to the breakthrough of macroscopic fractures, and a large number of cracks in the interior make high wave velocity areas, wave velocity abnormal areas change and transfer rapidly, and coal samples are already in unstable state. At the stage of true triaxial high load holding pressure, due to the continuous compaction of coal sample fractures and the full destruction of internal structure characteristics, the sustained damage occurred in coal samples, represented by the decreasing of low wave velocity region and the increasing of whole wave velocity. In addition, in the true triaxial loading stage, the accumulative fracture release energy distribution in the coal sample is relatively concentrated, and its position corresponds roughly to the high wave velocity region and the wave velocity anomaly area, and the maximum value also increases continuously. When the coal sample is unstable and destroyed, the accumulative fracture release energy distribution is gradually dispersed and penetrated through the whole sample, but the maximum growth rate of the coal sample tends to be flat.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD313

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