基于X-射线CT方法的岩石小裂纹扩展过程分析

岩石的小裂纹起裂及扩展过程是岩石力学研究的一个关键问题。对软硬两种砂岩进行单轴加载试验,同时用高分辨率的螺旋CT扫描机进行实时扫描。通过对获得的CT图像的分析处理发现,CT差值图像中的方差值与小裂纹的扩展速率有密切的关系,建立CT差值图像中的方差值与应力关系曲线,可以直观地看出:1)岩石样品中小裂纹起裂门槛值:软砂岩样品小裂纹扩展的门槛值为岩石强度的55%,小裂纹的扩展强度占整个强度的73%。硬砂岩小裂纹扩展的门槛值为岩石强度的64.5%,小裂纹的疲劳强度占整个强度的79%;2)小裂纹的扩展规律,即:在加载的初期岩石中小裂纹的扩展速率缓慢增大,在小裂纹扩展的门槛值出现之前快速下降,小裂纹扩展的门槛值出现之后又快速增加,最后当裂纹长度达到一定值时与长裂纹扩展速率基本一致。

Microfracturing Processes of Rock by Real-Time Observation of X-ray CT

To understand the fundamental problems of earthquake occurrence in detail,the determination of microfracturing and propogating in inner rock is considered to be useful for real-time detecting.Two types of sandstones are scanned by multislice spiral CT(MSCT) with high resolution under uniaxial compressive condition.Acorreding to the treatment and analysis of CT images,it is found that the variances of the difference of CT images are concerned closely with the propagating rate of microfractures.The relation curves between this variances and stresses of sandstone samples indicate the threshold value of microfractures propagating in sandstone samples can be identified easily.For a soft sandstone,the initiation of microfractures is 55% of the peak strength of a sandstone samples,and the whole propagating strength of microfractures is about 73% of the peak strength of a sandstone sample.For the hardy sandstone,the initiation of microfractures is 64.5% of the peak strength,and the whole propagating strength of microfractures is about 79% of the peak strength of a sandstone sample.And the propagating process of microfractures in the sandstones can be found intuitively.During the initial stage of compression,the propagating rate of microfractures increases very slowly with the enhanced compression.When the compression approaches to the threshold values of microfracturing initiation,the propagating rate of microfractures is decline rapidly.After the microfracturing initiation,the propagating rate of microfractures increases before the occurrence of macrofractures.