桩-砂土界面循环弱化宏细观机制

循环荷载下桩-土界面研究是桩土体系相互作用的重要研究方向,循环荷载下桩-土界面弱化效应主要包括界面剪应力循环弱化、界面法向应力循环弱化以及界面砂土颗粒破碎机制3部分,三者彼此影响共同制约桩-土界面的承载性能.界面粗糙度是影响桩-土界面力学机制的重要影响因素,为此,利用自主研发的可视化恒刚度界面剪切仪结合数字图像技术（DIC）,研究不同界面粗糙度下桩-土界面循环弱化效应的宏细观机制.结果表明,界面剪应力、法向应力与剪切位移关系曲线分别呈“滞回环”和“碟”状发展；相同粗糙度下,界面剪应力、法向应力随循环次数的增加呈对数型弱化,界面粗糙度越大弱化系数越大；应力路径曲线呈“蝴蝶环”状发展,界面摩擦角随着界面相对粗糙度的增加而增大；界面剪切带随剪切循环数和界面粗糙度的增加逐渐增厚,30个循环剪切后剪切带厚度稳定在（4～5）D50；剪切带内颗粒破碎明显,相对破碎率为1.86%～10.25%,随粗糙度增大而增大.
The study of pile-soil interface under cyclic loading is an important research direction of pile-soil interaction. The degenerate effects of pile-soil interface under cyclic loading consist of degenerate shear stress, degenerate normal stress, and the breakage mechanism of sand particles, which interact with each other and control the bearing capacity of pile-soil interface. Interfacial roughness has important influence on pile-soil mechanical mechanism. Macroscopic and microscopic mechanism of cyclic degradation behavior on pile-sand interface under different interface roughness was researched by utilizing self-developed visual constant normal stiffness (CNS) interface shear apparatus combined with digital image correlation (DIC) measurement technology. The experimental results showed that the relation curves of shear stress and normal stress developed as “hysteretic loop” and “disk” shapes, respectively. Under the same roughness, the interfacial shear stress and the normal stress both degraded logarithmically with the increase of the numbers of the cycles, while this degradation rate increased with the increase of interfacial roughness. The stress path curve developed as a “butterfly ring” shape, and the friction angle increased with the increase of interfacial relative roughness. The interfacial shear band was gradually thickened with the increase of shear cycles and interface roughness, and this thickness reached about (4-5) D50 after 30 cycles. In addition, the particles in the shear band were significantly broken and the relative crushing rate was 1.86%-10.25%, which increased with the increase of interfacial roughness.