薄层充填岩石节理剪胀特性试验研究

Experimental study on shear dilatancy characteristics of thinly-infilled rock joints

岩石节理剪胀特性是影响节理渗流的重要因素,主要受节理表面粗糙性和法向应力的影响。而对于充填岩石节理而言,其剪胀特性还受到充填介质的影响。为了研究薄层充填岩石节理的剪胀特性,首先制备了3组具有Barton标准剖面线形貌特征、充填度△=0.00,0.25,0.50,0.75及1.00的薄层充填模拟岩石节理试件,然后在低、中、高三级法向应力下进行直剪试验,得到了薄层充填岩石节理试件法向位移–剪切位移曲线及其破坏特征。结果表明:在低法向应力条件下,节理表面粗糙性和充填度共同影响薄层充填岩石节理试件的剪胀特性,而在中高法向应力条件下,节理表面粗糙性是影响其剪胀特性的关键因素;薄层充填岩石节理破坏特征包含充填介质的剪切挤碎和节理上下表面粗糙凸起体被剪断两种,且随着充填度的增加,充填介质剪切挤碎逐渐占主导地位,成为薄层充填岩石节理试件的主要破坏特征。在此基础上,考虑充填介质对节理表面粗糙度系数JRC的弱化作用,建立了薄层充填岩石节理峰值剪胀角随充填度呈指数变化的经验关系式,并通过直剪试验数据和已有文献数据对其适用性进行了初步分析。

The shear dilatancy has a significant effect on the seepage properties of rock joints,which is influenced by the roughness and normal stress acting on the rock joint surface.However,except for joint the surface roughness and normal stress,the infills also have an important effect on the shear dilatancy of infilled rock joints.So,in order to investigate the shear dilatancy of thinly-infilled rock joints,three groups of specimens which have the same surface roughness as Barton’s standard profiles and different infill thicknesses are prepared firstly.Then the direct shear tests are performed on these specimens under three levels of normal stress,and the normal displacement vs.shear displacement curves and failure characteristics of thinly-infilled rock joints are obtained.The results show that the shear dilatancy is influenced by both the surface roughness and the infill thickness under low normal stress condition,whereas the surface roughness is the key factor influencing the shear dilatancy under middle and high levels of the normal stress.Furthermore,the failure modes of specimens include the shear and crush of infill particles and the shear of surface asperities,and the former failure mode becomes dominant with the increase of infill thickness.Then an empirical exponential expression is proposed to describe the peak shear dilatancy angle of thinly-infilled rock joints quantitatively by considering the weakening effect of infills on joint surface roughness,which is validated preliminarily by the direct shear test results and published data in literatures.