Dynamic response and damage constitutive model of freeze-thawed sandstone with or without filling materials in prefabricated flaws

Abstract

In cold regions, flawed rocks are inevitably affected by freeze-thaw (FT) weathering and dynamic impact, and grouting or filling has become an effective means to improve their stability. In order to clarify the mechanical properties of flawed rocks with or without filling materials under dynamic loading, a series of FT cycle tests and impact tests were conducted on sandstone. The results indicate that the number of FT cycles significantly deteriorates the dynamic peak strength, apparent stiffness, and energy parameters, which are strongly correlated with the flaw inclination angle. In addition, the mechanical properties and energy absorption capacity of the filled specimens were significantly improved, but were affected by the number of FT cycles and flaw inclination angle. The strength and energy enhancement coefficients of all specimens are between 0.01 and 0.31 and 0.06–0.61, respectively. Based on the test results, a coupled damage model of the flawed rock under the combined action of FT cycles and impact loads is proposed, and then a dynamic damage constitutive model is established and verified accordingly, effectively characterizing the dynamic mechanical response of rocks with different FT cycles, flaw inclination angles, and filling states. Based on the principles of stress wave propagation and fracture mechanics, the filling reinforcement effect of rocks was explored. The filling material reduces the reflection of stress waves at the crack interface, enhances the propagation of stress waves, and thus reduces the adverse effects of impact loads on rocks. In addition, the filling material improves the uniformity of stress distribution at the crack tip, increases the stress intensity factor, and significantly enhances the bearing capacity of the rock. The filling effect depends on the matching of mechanical properties between the material and the rock. Therefore, when selecting filling materials, it is necessary to consider whether their FT degradation laws correspond to the rocks that need to be reinforced. The results contribute to clarifying the dynamic mechanical properties of flawed rocks in cold regions, providing guidance for the selection of filling materials and the reinforcement of fractured rock masses.