Weakening effect of various pore fluids on the tensile strength of granite

Laboratory three-point bending experiments are carried out to evaluate the effect of various fluids on the tensile strength of granite. The granite specimens were tested under both dry and saturated conditions. The fluids used to saturate the granite include distilled water, hydrochloric acid (HCl), sodium hydroxide (NaOH), kerosene, and hydraulic oil. The experimental results indicate the strength of granite is decreased when saturated by fluids compared to its value measured from dry samples. Compared to the dry granite specimens, water, HCl, NaOH, kerosene, and hydraulic oil reduce the tensile strength of granite by 26, 37, 28, 23, and 41%, respectively. The test data indicates that non-aqueous solution does not have noticeably different effect on reduction of the tensile strength compared to the aqueous solution. However, fluid viscosity is found to have profound impact on the results as a more viscous non-aqueous solution, hydraulic oil, greatly lowers the strength compared with those specimens saturated with less viscous kerosene. The experiments suggest that chemical fluid-rock interaction plays a minimal role in such constant loading rate tests that the failure occurs rapidly. On the other hand, the mechanical influence of the fluid, such as lubrication of grain boundaries and/or local pore pressure generation might play an important role in the determination of the strength of granite.