循环荷载作用下非饱和盐化粉土动力特性

西北地区机场若采用盐化粉土进行道基填筑，在飞机滑行荷载重复作用下，道基累积变形将成为影响机场服役性能的关键。为此，选取北方某地区粉土开展动三轴试验，研究循环荷载下不同含盐量(质量分数)对粉土动力特性的影响，并提出以累积塑性应变4%作为道基破坏标准的盐化粉土动强度预测模型。结果表明：随动应力幅值的增加，盐化粉土塑性变形逐渐由塑性安定状态向增量破坏转变；含盐量对粉土累积轴向应变、动模量、临界动应力有明显影响；相同动应力幅值下，当含盐量由0增加至5%时，试样累积轴向应变以1%含盐量为界限呈先减小后增加的趋势；低动应力幅值下，试样动模量随含盐量增加而逐渐衰减；从微观上对盐化粉土在1%低含盐量时强度短暂增强、高含盐量时强度逐渐衰减的现象进行分析，盐化粉土试样强度与土体孔隙中离子浓度以及土体颗粒排列方式有关；根据盐化粉土动强度预测模型，可得1%含盐量的土体塑性安定临界值约为5%含盐量土体的2.2倍。研究结果可为盐化粉土地区机场道基承荷能力设计提供参考。

Dynamic characteristics of unsaturated salinized silt under cyclic loading

Under long-term loading from aircraft, the cumulative deformation of airport subgrade filled with saline silt in northwest China can be a key factor that affects the service performance of the airport. Taking the silt in a typical area of northern China as example, the dynamic triaxial test was carried out to investigate the influence of salt content (mass fraction) on the dynamic characteristics of silt under cyclic loading. A cumulative plastic strain of 4% was selected as the failure strain based on the test results, and a prediction model of dynamic strength of salinized silt was proposed. Results show that with the increase in dynamic stress amplitude, the plastic deformation of salinized silt gradually changed from plastic stability to incremental failure. The salt content largely affected the cumulative axial strain, dynamic modulus, and critical dynamic stress of silt. At the same dynamic stress amplitude, as the salt content increased from 0 to 5%, the cumulative axial strain decreased firstly and then increased at the salt content of 1%. At low dynamic stress amplitude, the dynamic modulus decreased with the increase in salt content. The strength of salinized silt experienced a short growth at 1% salt content and a gradual attenuation at high salt content, which might be explained from a microscopic view that the strength of salinized silt sample was closely related to the ion concentration in the soil pores and the arrangement of soil particles. According to the dynamic strength prediction model, the critical dynamic stress for the silt with 1% salt content was about 2.2 times that of silt with 5% salt content. The conclusions of the study can provide reference for the airport runway design and construction in saline silt area.