Damage mechanism of soil-rock mixture after freeze-thaw cycles

Abstract

As a widely distributed geological and engineering material, the soil-rock mixture always undergoes frequentative and short-term freeze-thaw cycles in some regions. Its internal structure is destroyed seriously, but the damage mechanism is not clear. Based on the damage factor, the damage research of properties of soil-rock mixture after different times of freeze-thaw cycles is investigated. Firstly, the size-distributed subgrade gravelly soil samples are prepared and undergo different times of freeze-thaw cycles periodically (0, 3, 6, 10), and indoor large-scale triaxial tests are completed. Secondly, the degradation degree of elastic modulus is considered as a damage factor, and applied to macro damage analysis of soil-rock mixture. Finally, the mesoscopic simulation of the experiments is achieved by PFC3D, and the influence on strength between soil-rock particles caused by freeze-thaw cycles is analyzed. The results show that freeze-thaw cycles cause internal damage of samples by weakening the strength between mesoscopic soil-rock particles, and ultimately affect the macro properties. After freeze-thaw cycles, on the macro-scale, elastic modulus and shear strength of soil-rock mixture both decrease, and the decreasing degree is related to the times of cycles with the mathmatical quadratic form; on the meso-scale, freeze-thaw cycles mainly cause the degradation of the strength between soil-rock particles whose properties are different significantly.

摘要

土石混合体作为一种广泛分布的工程地质材料,在很多地区遭受频繁的短期冻融循环。其内部 结构受到严重损坏但破坏机理却不明晰。基于损伤因子,开展经历不同冻融次数下的土石混合体性 质的损伤研究。首先,准备级配试样使其经历不同次数冻融循环(0, 3, 6, 10),并进行大型三轴试验。 其次,将弹性模量衰减量视为损伤因子,应用于土石混合体宏观损伤研究。最后,利用PFC^3D 模拟试 验围观过程,分析冻融循环下土石颗粒间强度损伤影响。结果表明:冻融循环通过削弱土石颗粒间强 度进而引起内部微观损伤,并最终影响宏观性质。冻融循环后,宏观上,土石混合体弹性模量与剪切 模量均减小,且减小量与冻融次数为二次函数关系;微观上,冻融循环主要引起本身属性极大不同的 土与石颗粒间强度的衰减。