冻融循环作用下砂岩层进式损伤劣化规律研究

Investigation of progressive damage and deterioration of sandstone under freezing-thawing cycle

试验得到了试样直径、质量衰减量随冻融循环次数的变化规律,指出80次冻融循环是石英砂岩直径、质量变化线的拐点。提出了层进式损伤的CT精准识别技术方法,定义了试样主要损伤区并将其细分,分析了表层剥落前与剥落后的两阶段层进式冻融损伤过程,建立了CT值与弹性模量、孔隙率线性互推公式。分析认为:(1)40次冻融循环后,最外侧圈层弹性模量值为0,此时CT值不为0,圈层未剥落;(2)80次冻融循环后,最外侧圈层CT值为0,此时圈层孔隙率最大,圈层剥落;(3)试样内部圈层第2阶段劣化程度显著大于第1阶段劣化程度;在此基础上,提出了外圈层的束箍效应和内圈层的加速劣化效应,并从力学机制上进行了阐述。结合冻融循环次数下的孔隙率变化、弹模损失率变化、细观孔隙变化图像进一步定量阐明层进式损伤的发育演化规律。基于弹性模量、孔隙率分别随冻融循环次数变化规律,定义冻融弹性模量劣化因子ω,结合层进式区域划分,构建层进式损伤弹性模量劣化预测公式,并与实测值对比验证了上述方法的可行性。

The variations of the diameter and mass attenuation of rock samples with the number of freezing-thawing cycles are obtained,and it is pointed out that 80 freezing-thawing cycles are the inflection points of the variation lines of diameter and mass of quartz sandstone.A technical method for the accurate CT identification of progressive damage is proposed,and the main damage areas of the sample are defined and subdivided.Moreover,the freezing-thawing damage model of progressive damage at stages before and after spalling is also established.Linear relationships between CT value,elastic modulus and porosity are established,and it is concluded that:(1)After 40 freezing-thawing cycles,the elastic modulus of the outermost ring layer is 0,and the CT value is not 0 at this time.Additionally,the ring layer doesn’t peel off.(2)After 80 freezing-thawing cycles,the CT value of the outermost layer is 0.Meanwhile,the porosity of the layer is the largest and the layer is peeling off.(3)The deterioration of the inner layer of the sample at the second stage is significantly greater than that at the first stage.According to this finding,the bundle hoop effect of the outer layer and the accelerated degradation effect of the inner layer are proposed,which can also be explained based on the mechanical mechanism.On the basis of images of changes in porosity,loss rate of elastic modulus and mesopore after several freezing-thawing cycles,the development and evolution of progressive damage are further quantitatively illustrated.Based on the variation law of elastic modulus and porosity with the number of freezing-thawing cycles,respectively,the degradation factor"ω"of the freezing-thawing elastic modulus is defined,and a formula for predicting the elastic modulus degradation of progressive damage is also established based on the zone division of progressive damage.Finally,the feasibility of the above method is verified by comparing the calculated values with the measured values.