冻融循环作用下黄泛区饱和含盐粉土动力性能及细观损伤演化规律

山东省黄泛区地处季节性冻土区，当地大量采用含盐粉土修筑公路路基，冻融循环作用后路基土动力性能受损，在车辆荷载作用下会发生路基翻浆病害。为研究冻融作用、盐分含量对饱和路基粉土动力性能及细观结构特征的影响，针对不同含盐量粉土开展有侧限封闭冻融试验，采用振动三轴试验测试多次冻融作用后解冻状态土样的骨架曲线、动模量和动阻尼比，同时采用核磁共振技术测试经历多次冻融循环后解冻状态饱和土样的横向驰豫时间T₂谱曲线。研究结果表明：冻融作用后动应力幅值与动应变幅值之间符合修正的Hardin-Drnevich模型，当冻融6次后骨架曲线趋于稳定；初始动模量损伤度随冻融循环次数呈双曲线型增大，氯化盐含量小于12%时，随含盐量增加初始动模量损伤度呈线性增大；阻尼比随动应变幅值增大增加明显，随盐分含量、冻融次数增加而增大；随冻融次数增多，T₂谱曲线主峰信号强度幅值减小，同时会产生横向驰豫时间长的波峰；T₂级配曲线趋于连续光滑，形态趋于相似，不均匀系数和曲率系数趋于稳定；无盐粉土T₂级配曲线的不均匀系数逐渐减小，并约稳定于5.6，曲率系数先减小后增大，并约稳定于0.986；当经历冻融6次后，随含盐量增加，T₂级配曲线不均匀系数先增大后减小，曲率系数先减小后增大。

Dynamic Behavior and Meso-damage Evolution of Saturated Saline Silt from Yellow River Flooded Area Under Freeze-thaw Cycle

The Yellow River flooded area in Shandong Province belongs to a seasonal frozen region. Saline silt is widely used to construct a highway subgrade in this area. When subjected to a freeze-thaw cycle, the dynamic behavior of saline silt deteriorates, and mud pumping can occur in the subgrade under vehicle load. To investigate the influence of the freeze-thaw cycle and salt content on the dynamic behavior and meso-structure characteristic evolution of saturated saline silt, a lateral restraint closed-system freeze-thaw cycle test was conducted for saturated silt with different salt contents. The backbone curves, dynamic modulus, and damping ratio of the thawed soil samples after different freeze-thaw cycles were tested using cyclic triaxial tests. Simultaneously, nuclear magnetic resonance tests were conducted on the thawed soil samples after the freeze-thaw tests, and the spectrum curves of transverse relaxation time T₂ of the soil samples were obtained. The results show that the relationship between the dynamic stress and dynamic strain amplitudes after different freeze-thaw cycles can be described using the modified Harding-Drnevich model, and the backbone curves tend to be stable after the sixth freeze-thaw cycle. The damage degree of the initial dynamic modulus hyperbolically increases with the number of freeze-thaw cycles. When the chloride content is less than 12%, the damage degree of the initial dynamic modulus linearly increases with the salt content. The damping ratio significantly increases with increasing dynamic strain amplitude. The damping ratio also increases with the increase in the salt content and number of freeze-thaw cycles. The T₂ spectrum curves show that with the increase in the number of freeze-thaw cycles, the signal intensity of the main peak decreases, the number of peaks increases, and the new peaks have long transverse relaxation time. The T₂ gradation curves gradually tend to be continuous and smooth, and the shapes of the curves with the same salt content gradually become similar. The non-uniformity and curvature coefficients tend to be stable. The non-uniformity coefficient of the T₂ gradation curves of the salt-free silt gradually decreases and stabilizes at approximately 5.6, whereas the curvature coefficient initially decreases, then increases, and finally stabilizes at approximately 0.986. After being subjected to six freeze-thaw cycles, the non-uniformity coefficient of the T₂ gradation curves first increases and then decreases with the increase in the salt content, whereas the curvature coefficient first decreases and then increases with the increase in the salt content.