延迟时间对改良土现场施工具有重要意义。通过设计不同延迟时间下粉煤灰改良黄土的击实试验、无侧限抗压试验及直接剪切试验，研究分析延迟时间对粉煤灰改良黄土路基填料力学特性的影响，并通过扫描电镜试验对粉煤灰改良黄土的微观机理进行初步探讨分析。结果表明，随着延迟时间的增大，粉煤灰改良黄土的最大干密度先增大后减小，最优含水率呈先增大，接着变缓后又增大的趋势；无侧限抗压强度和直接剪切后强度均随延迟时间的增大逐渐减小，且与延迟时间有良好的线性拟合关系；改良土的黏聚力随着延迟时间的增大而减小，内摩擦角先增大后减小，且黏聚力的减小程度较内摩擦角大。微观结构分析得出，随着延迟时间的增加，改良土整体结构松散程度逐渐变大，由原来的大颗粒的团粒逐渐成为散粒。

Delay time is crucial in the field application of amended soils. Compaction tests, unconfined compressive strength tests, and direct shear tests were conducted on fly ash-amended loess under varying delay times to analyze the impact of delay time on the mechanical properties of subgrade fill materials. Preliminary microscopic mechanisms were explored through scanning electron microscopy. The results indicate that as delay time increases, the maximum dry density of the fly ash-amended loess initially increases and then decreases, while the optimal moisture content shows a trend of initial increase, followed by a plateau, and then another increase. Both unconfined compressive strength and shear strength are found to gradually decrease with longer delay times, displaying a strong linear correlation with delay time. The cohesion of the amended soil is observed to decrease with increasing delay times, while the internal angle of friction first increases and then decreases, with the reduction in cohesion being more significant than that in the internal angle of friction. Microstructural analysis reveals that with increasing delay times, the overall structure of the amended soil becomes looser, transitioning from larger aggregated particles to more dispersed ones.