饱和大理岩特征强度试验研究

为了研究水对岩石裂纹扩展活动的影响规律和机制,通过单轴压缩声发射试验,采用声发射法和体应变(含裂纹体应变)法确定干燥和饱和大理岩的特征强度,探讨声发射法确定大理岩特征强度的适用性和水对特征强度值变化的影响规律。结合特征强度附近声发射波形信号的主频统计结果,分析讨论水影响特征强度值的内在机制。结果表明:声发射法确定的大理岩起裂强度均小于宏观体应变法,其用于确定饱和岩样起裂强度有较强的适用性,但不适用于损伤强度的确定。岩样饱和后,其归一化起裂强度减小,归一化损伤强度增大。影响机制主要是孔隙水压力作用的强弱和裂纹扩展“阻碍力”。起裂点附近,孔隙水压力作用明显,岩石内部产生较多微观拉破坏,使裂纹在较低应力水平发生稳定扩展。扩容点附近,孔隙水压力作用弱化,产生裂纹扩展“阻碍力”,裂纹在较高应力水平发生非稳定性扩展。

Experimental study on the characteristic strength of saturated marble

The uniaxial compression acoustic emission(AE) tests of dry and saturated marble were carried out to study the effect mechanism of water on crack propagation. The characteristic strength of samples was determined by AE method and volumetric strain(crack volumetric strain) method. The applicability of AE method for determining the characteristic strength was discussed,and the effect mechanism of water on the characteristic strength was analyzed combining statistical analysis results of dominant frequency of AE waveforms in the vicinity of the characteristic strength. The results show that the strength threshold of crack initiation determined by AE method is lower than that by macro volumetric strain method. AE method can be suitably used to determine the strength threshold of crack initiation for saturated rock,whereas it is not appropriate to determine the damage strength threshold. The normalized crack initiation strength of samples decreases and the normalized damage strength increases after saturation. Effect factors of water on the normalized characteristic strength are the intensity of the pore water pressure and the crack growth resistance. Near the moment of crack initiation,the effect of the pore water pressure is obvious and there are many micro-tensile failures inside the rock,which makes crack develop stably at a lower stress level. Near the moment of volume dilation,the effect of the pore water pressure is weakened along with the existence of the crack growth resistance,which makes unstable crack propagation occur at a higher stress level.