【摘要】 为研究基坑开挖卸荷路径下土体的力学特征，开展了饱和粉土卸荷路径三轴排水剪切试验，获取了不同应力路径的应力应变曲线，分析了卸荷比、围压和应变水平对割线模量的影响，提出了饱和粉土卸荷模量简化公式。结果表明：不同卸荷应力路径的应力应变曲线均呈应变软化型，卸荷模量随卸荷比的减小、围压的增大而增大。K₀固结侧向卸荷路径（EB）的峰值剪应力高于K₀固结双向卸荷路径（EC、FD）；应力路径对割线模量衰减的影响程度差异显著，K₀固结双向卸荷路径（EC、FD）对割线模量衰减的影响最大。说明基坑坑底土体强度较高，受开挖的影响较小，抗变形能力较大，在基坑工程设计中，应考虑基坑不同区域对应的割线模量。更多还原

【Abstract】 The excavation of foundation pit engineering has different unloading effects on the surrounding soil. The existing specifications mainly use the consolidated undrained strength index based on the conventional triaxial tests, which cannot describe the mechanical characteristics of the excavation soil under the unloading path. The triaxial drainage shear tests on the unloading path of saturated silt are conducted, the stress-strain curves for different stress paths are obtained, the effects of unloading ratio, confining pressure and strain level on the secant modulus are analyzed, and a simplified formula proposed for the unloading modulus of saturated silt. The results show that the stress-strain curves of different unloading stress paths all exhibit a strain softening type, and the unloading modulus increases with a decrease in the unloading ratio and an increase in the confining pressure. The peak shear stress of K₀ consolidation lateral unloading path（EB） is higher than that of K₀ consolidation bidirectional unloading path（EC, FD）. The influences of the stress paths on the attenuation of the secant modulus vary significantly, with K₀ consolidation bidirectional unloading paths（EC, FD） having the greatest impact on the attenuation of the secant modulus. The strength of the soil at the bottom of the foundation pit is relatively high, and it is less affected by excavation, with a greater capability to resist deformation. In the design of foundation pit engineering, the corresponding secant modulus in different areas of the foundation pit should be considered.更多还原