Assessing the effect of freezing-thawing cycles on the results of the triaxial compressive strength test for calc-schist rock

Freezing-thawing (F-T) is an important mechanical weathering process in mountainous areas. Therefore, evaluating the effect of this phenomenon on rock properties is required for design in mining and rock engineering projects constructed in these areas. In this research, the influences of F-T cycles on triaxial compressive strength (TCS) test results were studied for calc-schist rock samples from the Angouran open-pit mine. For this purpose, 1200 m of drilling was performed in the mine in order to prepare the required specimens. About thirty calc-schist samples were tested at F-T cycles of 0, 7, 15, 40, and 75 and lateral stress of 0, 2, 4, 6, 8, and 10 MPa using the servo-control triaxial device. Each weathering cycle was conducted in 12 h of freezing and 12 h of thawing at - 20 degrees C to 20C degrees, respectively. Changes occurred in texture and microstructures of samples after weathering process were analyzed using the scanning electronic microscope (SEM). The SEM results showed the increase in micro- and macro-cracks in the samples structures and disappearance of cement in their matrix. Also, the results of TCS tests showed an exponential decrease in cohesion and internal friction angle with increasing the number of F-T cycles. As another finding of this study is that increasing the number of F-T cycles leads to a decrease in TCS values. Finally, an empirical equation is developed between TCS and number of F-T cycles for Angouran mine calc-schist.