Brittleness evolution characteristics of cyan sandstone under freeze-thaw cycles

In order to study the brittle characteristics and evolution law of the rock in the cold region, the freeze-thaw cycle test and triaxial compression test of the cyan sandstone were carried out. The brittleness evaluation index is used to quantify the brittleness of the cyan sandstone under the freeze-thaw cycle. Then the effects of freeze-thaw cycles and confining pressure on the brittleness of cyan sandstone are analyzed. Based on the sensitivity law of brittleness index of cyan sandstone to confining pressure, a brittle exponential evolution model with brittleness degradation factor beta and lithology characteristic lambda as parameters is established. Test data is verified by the same functional model. The results show that the brittleness of the cyan sandstone weakens with the increase of confining pressure and the rate of change of brittleness index shows strong sensitivity to confining pressure. The larger the confining pressure, the smaller the decay rate of the rock brittleness index under the same freeze-thaw cycles. Under the same confining pressure condition, the brittleness of the blue sandstone decreases with the increase of the number of freeze-thaw cycles, and the effect of brittleness degradation caused by unit freeze-thaw cycles increases with the number of freeze-thaw cycles. The brittleness exponential evolution model has a good correlation with the fitting data of freeze-thawed cyan sandstone, black sandstone and marble, and the parameters beta and lambda accurately reflect the brittle evolution characteristics of different freeze-thaw cycles and different rocks.