弯载下砂岩声发射特征值时间效应

Time-dependent behavior of acoustic emission feature parameters of sandstone under bending load

为探索开采速度对采空区顶板破断特征影响的力学机制,设定不同加载速率,开展砂岩3点弯曲和声发射试验,研究砂岩弯曲折断过程的力学行为及其受加载速度影响的时间效应和折断前兆特征。结果表明,加载速率越快,砂岩显著初始损伤声发射发生的应力条件越高,积累的应变能越高;岩石折断前,前兆声发射时间长度与加载速率呈指数负相关,加载速度越快,前兆声发射时间越短,可预测性越差;加载速率与砂岩折断声发射峰值能量及破坏载荷呈指数正相关,与砂岩折断声发射峰值计数呈指数负相关,加载速度越快,岩石折断所需的破坏荷载越大,峰值声发射计数越少,一次性释放的能量越高。上述岩石弯曲声发射特征值是加载速率的函数,存在时间效应。从机理上解释了煤矿开采速度越高,顶板岩体动力灾害危险性相对越高,可预测性越差的原因。

In order to explore the mechanical mechanism influence of mining rate on the characteristics of roof breaking in goaf,with different loading rates,a three point bending test of sandstone and acoustic emission testing was carried out to study the mechanical behaviour of bending fracture process of sandstone and the time effect by the loading rate and fracture precursor characteristics.The results show that the faster the loading rate is,the higher the stress condition of the significant initial damage acoustic emission is,and the higher the strain energy is.Before the rock breaks,the precursory AE time length is negatively correlated with the loading rate.The precursory AE time is shortened as loading rate increases,and its predictability is the worst.The loading rate is positively correlated with the peak AE energy and the failure load,which is negatively correlated with the peak value of AE counts.The faster loading rate is,the larger failure load energy is,the fewer the peak AE counts,and the higher the energy is released at one time.The above acoustic emission feature parameters of the rock are the function of loading rate,and time-dependent.This paper explains the reason why the higher the mining speed is,the higher the hazard of roof dynamic disaster is and the worse the predictability is from its mechanism aspect.