Measuring foliation tensile strength of metamorphic rock by using pull-off test

The tensile strength of rock is an important property of rock engineering. However, the measurement of the tensile strength of rock is often overlooked due to difficulties of specimen preparation and the accuracy of testing results. This study adopted the pull-off test to measure the foliation tensile strength of metamorphic rock such as slate, green schist, and black schist. Compared with contemporary tensile tests, this method is relatively simple and effective, with easy specimen preparation. Additionally, 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 recommends procedures for sample preparation and testing as well. The test results indicate that the black schist exhibited the greatest tensile strength and that the slate had the lowest strength. Besides this, the slate exhibited significant wetting deterioration. Examination of the failure patterns revealed that the failure planes of all specimens occurred on the foliation planes, indicating reasonable failure patterns. Finally, this study investigated the factors potentially affecting the validity of tensile strength measurement, including the failures occurring at (1) the preexisting joint during sample preparation and (2) the interface of rock and epoxy resin. Procedures for mitigating this effect were also suggested.