含不同胶结充填物的碳酸盐岩层面剪切力学特性试验研究

Experimental study of the shear behavior of carbonate bedding planes cemented by different materials

层面是层状岩体稳定性的主控结构面,层面的剪切力学行为及抗剪强度对建造于层状岩体中的地下工程具有重要影响。由于成岩时期物化作用的差异,同一工程场址常发育不同地质特征(胶结充填物、粗糙度等)的层面。为了深入了解不同类型层面的剪切力学特性,利用乌东德水电站地下厂房区域取得的胶结层面试样开展常法向应力及峰后降法向应力直剪试验。试验结果表明,不同地质特征的层面表现出不同的剪切力学行为,按有无明显峰值可将剪切变形–剪应力曲线分为2类,无明显峰值层面的粗糙度和表面附着物均有别于有明显峰值层面。法向变形与法向应力直接相关,但与层面类别之间的关系不明显。不同类型层面还表现出不同的剪胀行为及相应的剪胀角差异。胶结层面抗剪强度低于完整岩石但高于已分离层面,对层状岩体起弱化作用。按层面地质特征对其进行分类有助于进一步理解层状岩体的复杂力学行为,而选择不同层面力学模型可使计算更贴近实际工程岩体特征。

Abstract-. Bedding planes are of significant importance for the stability of layered rock mass. In order to perform detailed stability analysis for underground excavations in layered rock mass, it is necessary to gain sufficient knowledge of shear behavior and strength of bedding planes. Due to the complex physical and chemical processes involved during diagenesis, bedding planes exhibiting different geological features（cementation, roughness, etc） are often seen in a specific engineering site. In order to better characterize the shear behavior of these bedding planes, two types of shear tests, namely the constant normal stress tests and the post-peak stepwise-decreasing normal stress tests, were conducted using the cemented bedding plane samples obtained from underground caverns of Wudongde hydropower station. Test results showed that obviously different shear behavior corresponded to different geological features. The curves of shear displacement-shear stress were mainly divided into two groups according to their peak and residual behavior. The roughness and surface materials of groups with clear peak shear stress were different from the ones without peak. Direct relationship existed between the normal stiffness and normal stress, however, no obvious correlation was found between the normal stiffness and bedding plane types. Dilation behavior and the corresponding dilation angles of different kinds were also observed. The shear strength of cemented bedding planes is higher than the one of the separated bedding planes and lower than the one of the intact rock, which weakens the whole rock mass. A deeper understanding of rock mass behavior can be achieved when the geological variety of bedding planes is properly considered.