Abstract: Loess exhibits characteristics such as large pores, weak cementation and loose structure, making it prone to deterioration under wet-dry cycles, which can trigger foundation and engineering structure diseases in loess areas. Through uniaxial compression, axial fracturing, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) tests, the tensile and compressive mechanical properties and microstructures of lignin-modified loess under wet-dry cycles were systematically investigated. The results indicate that with an increase in lignin content, the silt content of the modified loess firstly increases and then decreases, while the clay content firstly decreases and then increases. Both the compressive and tensile strengths initially increase and then decrease with increasing lignin content, reaching an optimal dosage of 1.0%, at which point the brittleness is minimized. The structure of the modified soil is primarily characterized by point-to-surface contacts and embedded arrangements, while wet-dry cycle promotes a gradual shift in contact patterns towards point contact and aerial arrangement. The pore volume ratio of the samples firstly decreases and then increases with increasing lignin content, reaching its minimum at a dosage of 1.0%.

Key words: geotechnical engineering; loess; wet-dry cycles; lignin improvement; tensile-compressive strength characteristics; microstructure

摘要： 黄土具有大孔隙、弱胶结和结构疏松等特性，在干湿循环作用下易发生劣化，会引发黄土地基与工程结构病害。通过单轴压缩、轴向压裂、电镜扫描及核磁共振试验，系统研究了干湿循环条件下木质素改良黄土的拉-压力学特性与微观结构。结果表明：随木质素掺量增加，改良黄土的粉粒含量先增后减，黏粒含量先减后增；抗压与抗拉强度均随掺量增加呈先增强后减弱趋势，最佳掺量为1.0%，此时脆性最低；改良土体结构以点面接触和嵌固排列为主，干湿循环促使接触方式逐渐向点接触和架空排列转变；试样孔隙体积比随掺量增加先降后升，在1.0%掺量时达到最小。

关键词: 岩土工程； 黄土； 干湿循环； 木质素改良； 拉压强度特性； 微观结构