为探明上海深部砂土在中主应力σ₂影响下的强度和变形特性，对上海第7、9和11层深部砂土开展了多组真三轴试验，分析了不同中主应力系数b下的应力-应变和体积应变行为，阐明了摩擦角和破坏包络线随b的变化规律并对比了3层砂土之间的参数差异。结果表明，σ₂对上海深部砂土的强度和变形特性影响显著。砂土强度随b的增大而减小，而其剪胀性的变化规律则相反。第9层土展现出最明显的软化特性和剪胀性且强度最高；而第11层土则几乎展现出硬化和剪缩且强度最低。第7层土的特性处于第9和11层之间且更接近于第9层。SMP准则相较于L-D和M-C准则更适用于预测σ₂影响下的上海深部砂土强度指标。

To investigate the strength and deformation behaviors of Shanghai deep sands under the effect of intermediate principal stress (σ₂), multiple sets of true triaxial tests are conducted on Shanghai deep sand layers 7, 9, and 11. The stress-strain and volumetric strain behaviors under different coefficients of intermediate principal stress (b) are analyzed, and the variation laws of friction angles and failure envelopes with b are clarified. Additionally, the parameter differences between these 3 sand layers are compared. The results indicate that σ₂ has a significant impact on the strength and deformation behaviors of Shanghai deep sands. The strength decreases with the increase of b, while dilatancy changes in the opposite direction. Layer 9 exhibits the most significant softening characteristics and dilatancy with the highest strength, while layer 11 almost exhibits hardening and contraction with the lowest strength. The behaviors of layer 7 are between the two and closer to those of layer 9. Compared to the L-D and M-C criteria, the SMP criterion is more suitable for predicting the strength index of Shanghai deep sands under the effect of σ₂.