汶马高速公路千枚岩堆积体岩块定向性试验研究

汶川－马尔康高速公路（简称汶马高速）沿线发育大量的千枚岩堆积体，施工开挖形成的千枚岩堆积体边坡的稳定性显著影响着该公路施工及运营安全。以往对千枚岩堆积体的研究多将其视为均质碎块石土边坡，较少关注其特有的结构特征——千枚岩岩块的定向性，导致工程实践中边坡的失稳破坏。千枚岩为片理构造的变质岩，岩块具有显著的扁平化特征，沿坡运动后以一定的方向性停积。野外调研表明，堆积体中扁平状岩块的倾向与边坡坡面倾向相近，将此称之为岩块定向性，并认为该定向性是影响堆积体边坡稳定性的重要因素。以汶马高速千枚岩堆积体为研究对象，设计物理模型试验研究千枚岩堆积体岩块定向性特征及其影响因素。在此基础上开展考虑岩块定向特征的堆积体大型直接剪切试验，探索岩块定向性对千枚岩堆积体边坡稳定性的影响。结果表明，坡度及堆积体中细颗粒含量对岩块定向性有显著影响，坡度为20°～30°时，定向性最明显，且随细颗粒的含量增大而增大；边坡稳定性分析时的潜在滑面抗剪强度由于岩块定向性而显著降低。

Experimental study of fragment orientation of phyllite talus at Whenchuan-Maerkang expressway

Slope failure frequently occurred during and after the excavation of phyllite talus at the Wenchuan-Maerkang expressway. Previous research on phyllite talus has mainly considered it as homogeneous soil, while its unique structural features, such as the orientation of the constituted phyllite fragments, is less concerned. Phyllite is a metamorphic rock with foliated structure, and phyllite fragments are characterized with their flattened shape that may cause them to stop accumulating along the slope in a certain orientation. Field investigation shows that the dip direction of the phyllite fragments is usually parallel to or forms only a small angle to the talus slope inclination, which is defined as fragment orientation in this paper. The fragment orientation is considered as an important factor contributing to the slope instability of phyllite talus. Model tests are designed to study the orientation characteristics of the phyllite fragments and its influencing factors by taking the phyllite talus at Wenchuan–Maerkang expressway as examples. Large-scale direct shearing test considering the fragment orientation are consequently performed to explore the effects of fragment orientation on slope stability of phyllite talus. The results show that the slope angle and the content of fine particles in the talus have significant influence over the fragment orientation; when the slope angle is 20°-30°, the orientation is most obvious and rises with the increase of fine particle content; the shearing strength parameters of phyllite talus for slope stability analysis significantly reduce due to the fragment orientation.