Feng Meimei, Cao Xiaoxiao, Wu Taifeng, Yuan Kangsheng
State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China.
School of Mechanics & Civil Engineering, China University of Mining & Technology, Xuzhou 221116, China.
Materials (Basel). 2024 Dec 2;17(23):5905. doi: 10.3390/ma17235905.
In order to investigate the impact of freeze-thaw damage on sandstone under the coupling of ground stress and pore water pressure, three types of porous sandstone were subjected to freezing at different negative temperatures (-5 °C, -10 °C, -15 °C, and -20 °C). Subsequently, hydraulic coupling triaxial compression tests were conducted on the frozen and thawed sandstone. We analyzed the effects of porosity and freezing temperature on the mechanical properties of sandstone under hydraulic coupling and performed nuclear magnetic resonance tests on sandstone samples before and after freezing and thawing. The evolution of the pore structure in sandstone at various freezing and thawing stages was studied, and a statistical damage constitutive model was established to validate the test results. The results indicate that the stress-strain curves of sandstone samples under triaxial compression after a freeze-thaw cycle exhibit minimal changes compared to those without freezing at normal temperature. The peak deviator stress shows a decreasing trend with decreasing freezing temperature, particularly between -5 °C and -10 °C, and then gradually stabilizes. The elastic modulus of sandstone with different porosity decreases with the decrease in freezing temperature, and the decrease is more obvious in the range of -5 °C~-10 °C, decreasing by 2.33%, 6.11%, and 10.5%, respectively. Below -10 °C, the elastic modulus becomes similar to that at -10 °C, and the change tends to stabilize. The nuclear magnetic porosity of sandstone samples significantly increases after freezing and thawing. The smaller the initial porosity, the greater the rate of change in nuclear magnetic porosity after a freeze-thaw cycle. The effects of freeze-thaw damage on the T2 distribution of sandstone with different porosity levels vary. We established a statistical damage constitutive model considering the combined effects of freeze-thaw damage, ground stress, and pore water pressure. The compaction coefficient was introduced into the constitutive model for optimization. The change trend of the theoretical curve closely aligns with that of the test curve, better characterizing the stress-strain relationship of sandstone under complex pressure environments. The research findings can provide a scientific basis for wellbore wall design and subsequent maintenance in complex environments.
为了研究地应力与孔隙水压力耦合作用下冻融损伤对砂岩的影响，对三种类型的多孔砂岩在不同负温度（-5℃、-10℃、-15℃和-20℃）下进行冷冻。随后，对冻融后的砂岩进行水力耦合三轴压缩试验。分析了孔隙率和冷冻温度对水力耦合作用下砂岩力学性能的影响，并对砂岩样品冻融前后进行核磁共振试验。研究了砂岩在不同冻融阶段孔隙结构的演化，并建立统计损伤本构模型来验证试验结果。结果表明，与常温下未冷冻的砂岩相比，冻融循环后三轴压缩下砂岩样品的应力-应变曲线变化极小。峰值偏应力随冷冻温度降低呈下降趋势，尤其在-5℃至-10℃之间，然后逐渐稳定。不同孔隙率砂岩的弹性模量随冷冻温度降低而减小，在-5℃~-10℃范围内减小更为明显，分别降低了2.33%、6.11%和10.5%。低于-10℃时，弹性模量与-10℃时相似，变化趋于稳定。砂岩样品冻融后核磁共振孔隙率显著增加。初始孔隙率越小，冻融循环后核磁共振孔隙率的变化率越大。冻融损伤对不同孔隙率水平砂岩的T2分布影响各异。建立了考虑冻融损伤、地应力和孔隙水压力综合作用的统计损伤本构模型。将压实系数引入本构模型进行优化。理论曲线的变化趋势与试验曲线紧密吻合，能更好地表征复杂压力环境下砂岩的应力-应变关系。研究结果可为复杂环境下的井筒壁设计及后续维护提供科学依据。
