Study of the degradation and microstructural characteristics of granite porphyry with freeze–thaw cycles

Abstract

Abstract In this research, the microstructural damage and the degradation law are investigated for the rock mass in open-pit mine slopes with freeze–thaw cycles. Taking four different freeze–thaw cycles (0, 9, 18, and 27) of saturated granite porphyry as the research object, a scanning electron microscope (SEM) and nuclear magnetic resonance technology were used to test the changes in the composition, internal pores, cracks, and morphology characteristics of saturated granite porphyry before and after the freeze–thaw cycles. The microscopic structural characteristics such as the mass loss rate, wave velocity, porosity, and total T 2 spectral area of the saturated granite porphyry under different working conditions were analysed. A damage degradation prediction model for saturated granite porphyry under freeze–thaw cycle conditions was also established. The results showed that, (1) The quality of the saturated granite porphyry increased with the increase in the number of freeze–thaw cycles, while the wave velocity decreased with the increase in the number of freeze–thaw cycles. (2) During the freeze–thaw process, the saturated granite porphyry underwent crack propagation along its primary joints. As the number of freeze–thaw cycles increased, the microstructure exhibited a significant weakening effect, and the damage to the microstructure further deteriorated the macroscopic mechanical properties. (3) As the number of freeze–thaw cycles increased, the change in the porosity of the saturated granite porphyry became positively correlated with the number of freeze–thaw cycles. The number of small and large pores inside the rock mass significantly increased, and the small pore structure expanded and developed into large pores. (4) The prediction model of wave velocity deterioration of granite porphyry under the condition of freeze-thaw cycle accords with the exponential function, and the model has a high fitting degree (R 2 = 0.993). This model provides a deterioration constant with guiding significance for the durability of rock mass under the action of freeze-thaw cycle, and can well reflect the deterioration law of saturated granite porphyry under different freeze-thaw cycle times.

Keywords

• Freeze–thaw cycle
• Granite porphyry
• Damage deterioration
• Microscopic structure
• Porosity