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冻融损伤石英岩力学特性及损伤本构模型
Mechanical Characteristics and Damage Constitutive Model of Quartzite under Freeze-thaw Cycles
西南艰险山区分布有大量岩质边坡,长期冻融作用引起岩体力学性能发生劣化,进一步导致边坡稳定性降低。为研究岩体在冻融作用下的损伤劣化规律,选取某高陡边坡工程的低孔隙率石英岩进行不同冻融循环次数条件下的单轴压缩试验,分析其力学劣化和能量演化规律,并基于能量演化规律提出岩石完全压密点的确定方法,以完全压密点为分段点建立考虑压密段的岩石分段损伤本构模型。研究结果表明:前期冻融循环作用对石英岩的影响较小,当冻融循环次数>40时,石英岩的力学性能出现明显劣化,破坏模式由剪切破坏逐渐向拉-剪复合破坏转变;确定弹性能耗比K(耗散能/弹性应变能)为1.2对应的点为完全压密点,压密应变随冻融循环次数的增加呈线性增大;考虑压密段的岩石分段损伤本构模型与试验数据的匹配度较好,可更准确地描述冻融损伤石英岩的变形破坏特性。
There are a large number of rock slopes in the difficult and dangerous mountainous areas of southwest China. Long-term freeze-thaw action deteriorates the mechanical properties of the rock mass, leading to decreased slope stability. To study the damage degradation law of rock mass under freeze-thaw action, uniaxial compression tests were conducted on low-porosity quartzite from a high and steep slope in the southwest hazardous mountainous area. The mechanical deterioration and energy evolution were analyzed. Based on the energy evolution law, a method for determining the complete compaction point of rock was proposed. A piecewise damage constitutive model of the rock in consideration of the compaction section was established by taking the complete compaction point as the piecewise point. Results show that early freeze-thaw cycles have little effect on the quartzite. However, when the number of freeze-thaw cycles exceeds 40, the mechanical properties of quartzite deteriorate significantly, and the failure mode gradually changes from shear failure to a combination of tensile and shear failure. The point corresponding to an elastic energy consumption ratio K (ratio of dissipated energy to elastic energy) of 1.2 is determined as the complete compaction point. The strain corresponding to the complete compaction point increases linearly with the increase in freeze-thaw cycles. The proposed piecewise damage constitutive model matches well with experimental data and more accurately describes the deformation and failure characteristics of freeze-thaw damaged quartzite.
冻融循环 / 石英岩 / 力学劣化 / 能量演化 / 完全压密点 / 分段损伤本构模型
freeze-thaw cycles / quartzite / mechanical degradation / energy evolution / complete compaction point / piecewise damage constitutive model
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Geotechnical projects in cold regions suffer from both cyclic freezing-thawing and excavation unloading, giving rise to rock degradation. In this article, the strength characteristics and damage characteristics of sandstone subjected to both cyclic freezing-thawing and excavation unloading are analyzed systematically by freeze-thaw cycle test and triaxial unloading test. The results are concluded as follows: in freeze-thaw cycle test, the sandstone experienced a stage from tension failure gradually to shear failure as confining pressure rises; as the freeze-thaw cycle proceeds, the sandstone witnessed an apparent lateral expansion in the middle, with different levels of tension cracks, circular cracks, rock powder and rock fragments; while in triaxial unloading test, as freezing-thawing proceeds, the peak strength of sandstone reduces, and dilatancy stress declines in an exponential relation; destructive confining pressure is in a quadratic functional relation with cycle number; moreover, the freeze-thaw damage value increases linearly with the number of freeze-thaw cycles, indicating that the effect of cyclic freezing and thawing intensifies gradually.
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