考虑真实接触微凸体的岩石节理三维粗糙度指标

A 3D quantified surface description for rock joint based on the real contact asperities

节理在压剪作用下,仅仅是一小部分较陡微凸体发生接触而相互作用。以往在描述粗糙度时是考虑整个形貌面微凸体的分布特点,这使得所得粗糙度指标弱化了较陡微凸体作用而强化了较平缓微凸体对剪切强度的作用(实际上大多平缓微凸体在剪切过程中未接触)。为考虑实际接触节理的粗糙度,基于Grasselli视倾角分布函数研究了不同视倾角的面积比含量,分析了较陡接触微凸体对节理抗剪强度的作用。对于完全耦合的并且没有填充物的节理,当承受法向荷载时,节理少部分接触微凸体会发生弹性变形,在最初接触的微凸体部分会发生屈服。随着法向应力继续增加,会有更多的微凸体相互接触并发生屈服,这一过程会连续发生直至相互接触的微凸体面积足够大能够承受给定法向荷载的作用。因此,所有接触微凸体中的最小倾角为在一定荷载作用下刚好屈服的微凸体的倾角。对于岩石节理在法向应力下的剪切问题,实际接触面积可以近似认为是作用在节理面上法向荷载除以岩石的单轴抗压强度。考虑实际接触部分节理微凸体分布特征,获取了实际接触节理微凸体平均有效视倾角,得到了合理的三维粗糙度指标。采用巴西劈裂试验方法获取岩石节理面,扫描并获取了节理形貌坐标数据,用以研究节理表面粗糙度。节理峰值剪胀角反映了在某一法向应力下节理的剪切性质,并且可以准确的反映节理峰值抗剪强度。对比分析了实际接触节理粗糙度与节理峰值剪胀角趋势变化,结果表明节理粗糙度新指标可以与节理峰值抗剪强度很好地联系起来。

Under the action of compression and shear loads,only a small part of the steep asperities on the joint surface contacts and interacts with each other.In the past,when describing the roughness,the distribution characteristics of the asperities of the whole surface were considered,which made the roughness index weaken the effect of the steeper asperities and strengthen the effect of the gentler asperities on the shear strength(in fact,most of the gentler asperities did not contact during the shear process).Firstly,the area ratio of different apparent angles was studied based on the Grasselli apparent angle distribution function.The effect of the steeper contact asperities on joint shear strength was analyzed.For fully coupled joints without filling,when the joints are subjected to normal load,a small part of asperities will undergo elastic deformation,and the initial contact part will yield.As the normal stress continues to increase,more and more asperities will contact with each other and yield.This process will continue until the area of the contact asperities is large enough to withstand the given normal load.Therefore,the minimum dip angle of all contact asperities is the dip angle of the asperities which just yield under a certain load.Furthermore,the approximate expression of the actual contact area was obtained based on the contact theory.Considering the distribution characteristics of the actual contact part of the joint asperities,the average effective apparent angle of the actual contact joint asperities was obtained,and the reasonable 3D roughness index was obtained.The Brazilian splitting test was carried out to obtain the splitting joint surface instead of the natural joint surface to study the joint roughness,and the joint coordinate data was obtained through the scanning test of the joint morphology surface.The peak dilatation angle of joint reflects the actual shear process under a certain stress,and can accurately reflect the peak shear strength of joint.The results show that the new index of joint roughness can be well related to the peak shear strength of joints.