The tensile strength of rock is an important property of rock engineering. However, the measurement of tensile strength of rock is often overlooked due to difficulties of specimen preparation and accuracy of testing result. This study adopted the pull-off test to measure the foliation tensile strength of metamorphic rock, including slate, green schist and black schist. Compared with contemporary tensile tests, this method is relatively simple and effective, with easy specimen preparation. Besides, this approach can be conducted not only in the laboratory but also in the field, which is quite useful for evaluating the rock slope stability. This study suggested the procedures of sample preparation and testing as well. The test results indicate that the black schist exhibited the greatest tensile strength, and the slate had the lowest strength. Besides, the slate exhibited significant wetting deterioration. To examine the failure patterns, the failure planes of all specimens occurred on the foliation planes, indicating reasonable failure patterns.
Foliation is a geological structure formed by shearing forces or differential pressure during regional metamorphism history. Compared to other discontinuities, the foliation is repetitive layering with sheet-like planar structures, and common exists in metamorphic rocks, such as slate, phyllite and schist. In geology, the foliation is a significant feature to distinguish the level of metamorphism in rocks. In engineering, the presence of foliation causes rocks to exhibit high anisotropy and heterogeneity, which greatly influence the analysis of mechanical properties. Foliated metamorphic rocks are easily split along the direction of foliation under external loading; consequently, the properties of foliation heavily influence rock engineering with respect to stability. For instance, in metamorphic rock slopes with strong foliation, interlayer splitting along foliation occurs frequently, inducing toppling failure to form bending folds in the upper slope and subsequent rock falls. (Weng et al., 2015; Lo and Weng, 2016). In addition, because of the wetting process, the strength of foliation commonly decreases significantly. Therefore, how to evaluate the tensile strength of foliation under different environmental conditions is an important issue of rock mechanics and associated engineering.
