含水率对松软煤体波速及破坏特征影响的试验研究

Effect of moisture content on wave velocity and failure characteristics of soft coal

为研究含水率对松软煤体超声波波速与破坏特征的影响,针对不同含水状态型煤试样,采用岩石力学试验机(mechanical testing&simulation,简称MTS)、超声波监测仪,结合图像处理技术(digital image correlation,简称DIC)开展单轴压缩条件下煤体波速、表面形态监测试验,分析波速及变形演化特征;运用计算机断层(computed tomography,简称CT)扫描试验系统进行破坏煤体细观结构观测试验,获取三维裂隙分布形态和特征参数;探讨初始波速和破坏煤体波速随含水率变化规律。研究结果表明:(1)随轴向应变的增加,各含水率下煤体波速均呈现平稳-缓慢下降-急剧下降-再平稳4个变化阶段,且随含水率的增加,波速变化的缓慢下降、急剧和再平稳现象均推迟启动。(2)煤体初始波速及破坏后波速随含水率的增加均先增后减,荷载作用后煤体波速降低值与含水率呈线性关系。(3)随含水率的增加,破坏煤体内部裂隙表面积、裂隙体积及三维分形维数均具有线性增大的变化趋势,煤体由剪切破坏向拉伸破坏转变。(4)微观结构是导致各含水率下煤体初始波速差异的主要原因,而破坏煤体波速由微观结构和细观裂隙分布共同决定。研究结果可为揭示注水煤体声学力学响应特征,防控失稳灾害提供试验依据。

In order to study the effect of moisture content on ultrasonic wave velocity and failure characteristics of soft coal,the mechanical testing&simulation(MTS)rock mechanics experimental machine,ultrasonic detector,and digital image correlation(DIC)processing technology were employed to conduct monitoring experiments on the wave velocity and surface morphology of briquette samples with different moisture contents under uniaxial compression.The evolution characteristics of wave velocity and deformation were analyzed.The computed tomography(CT)scanning test system was used to observe the meso-structure of failed coal,and the three-dimensional fissure distribution and characteristic parameters were obtained.The change laws of initial wave velocity and wave velocity of failed coal with moisture content were explored.The results show that:(1)With the increase of axial strain,the wave velocity of coal under different moisture contents exhibits four stages:steady,slowly decreasing,sharply decreasing,and then becoming steady again.As moisture content increases,the onset of the slowly decreasing,sharply decreasing,and then becoming steady stages of wave velocity change is delayed.(2)The initial wave velocity and post-failure wave velocity of coal increase and then decrease with the increase of moisture content,and the decrease in coal wave velocity after loading is linearly related to the moisture content.(3)As moisture content increases,the surface area,volume,and three-dimensional fractal dimension of internal fissures in the damaged coal show a linear increasing trend,and the failure mode of coal transitions from shear failure to tensile failure.(4)The microstructure is the main reason for the difference in initial wave velocity of coal under different moisture contents,while the wave velocity of the damaged coal is determined by both the microstructure and the distribution of meso-fissures.The research results can provide an experimental basis for revealing the acoustic-mechanical response characteristics of water-injected coal and for preventing and controlling instability disasters.