Chang Dan, Xie Yongjun, Zhang Xinghua, Liu Jiankun
School of Civil Engineering, Sun Yat-sen University, Guangzhou 510275, China.
Guangdong Key Laboratory of Marine Civil Engineering, School of Civil Engineering, Sun Yat-sen University, Guangzhou 510275, China.
Polymers (Basel). 2025 Feb 27;17(5):644. doi: 10.3390/polym17050644.
The mechanical properties and envelope curve predictions of polyurethane-improved calcareous sand are significantly influenced by the magnitude and direction of principal stress. This study conducted a series of directional shearing tests with varying polyurethane contents ( = 2.5%, 5%, and 7.5%), stress Lode angles (θσ = -19.1°, 0°, 19.1°, and 30°), and major principal stress angles ( = 0°, 30°, 45°, 60°, and 90°) to investigate the strength and non-coaxial characteristics of calcareous sand improved by polyurethane foam adhesive (PFA). Key findings revealed that failure strength varied significantly with the major principal stress axis direction, initially decreasing to a minimum at α = 45° before increasing, with a 30% decrease and 25% increase observed at = 5%. Non-coaxial characteristics between strain increment and stress directions became more pronounced, with angles varying up to 15°. Increasing polyurethane content from 2.5% to 7.5% enhanced sample strength by 20% at θσ = -19.1° and = 60°. A generalized linear strength theory in the π-plane accurately described strength envelope variations, while a modified Lade criterion, incorporating polymer content, effectively predicted multiaxial strength characteristics with less than 10% deviation from experimental results. These contributions provide quantitative insights into failure strength and non-coaxial behavior, introduce a robust strength prediction framework, and enhance multiaxial strength prediction accuracy, advancing the understanding of polyurethane-improved calcareous sand for engineering applications.
聚氨酯改良钙质砂的力学性能和包络曲线预测受主应力大小和方向的显著影响。本研究进行了一系列定向剪切试验，试验中聚氨酯含量（分别为2.5%、5%和7.5%）、应力洛德角（θσ = -19.1°、0°、19.1°和30°）以及主应力角（α = 0°、30°、45°、60°和90°）各不相同，以研究聚氨酯泡沫胶粘剂（PFA）改良钙质砂的强度和非共轴特性。主要研究结果表明，破坏强度随主应力轴方向变化显著，在α = 45°之前先降至最低，之后上升，在含量为5%时，强度下降30%，上升25%。应变增量与应力方向之间的非共轴特性变得更加明显，角度变化可达15°。在θσ = -19.1°和α = 60°时，聚氨酯含量从2.5%增加到7.5%可使样品强度提高20%。π平面中的广义线性强度理论准确描述了强度包络线的变化，而结合聚合物含量的修正拉德准则能有效预测多轴强度特性，与实验结果的偏差小于10%。这些研究成果为破坏强度和非共轴行为提供了定量见解，引入了一个强大的强度预测框架，提高了多轴强度预测精度，推动了对聚氨酯改良钙质砂在工程应用方面的理解。
