The interface between unsaturated soil and structure plays an important role in various geotechnical structures in natural environment. In this study, a series of three-dimensional numerical direct shear tests are conducted on a soil-structure interface under various suctions and normal stresses by using the discrete element method (DEM). The simulated macro-mechanical results match reasonably well with experimental data reported in the literature. During the shearing process, the micro-mechanical shearing properties between unsaturated soil and structure are investigated, including particle displacement, the magnitude and orientation of the contact force, and the magnitude and orientation of the capillary force. The influence of capillary cohesion on the macro- and micro-mechanical behavior of the interface changes non-monotonically with the suction increase. Samples with the suction (or degree of saturation) in the funicular regime usually show more distinct capillary cohesion effect compared with that in either capillary or pendular regimes. The capillary cohesion effect on unsaturated soil-structure interfacial behavior is weakened with increasing normal stress.

非饱和土与结构之间的界面在自然环境中的各种岩土结构中起着重要作用。在这项研究中，使用离散元方法（DEM）在各种吸力和法向应力下的土 - 结构界面上进行了一系列三维数值直剪试验。模拟的宏观力学结果与文献中报道的实验数据相当吻合。在剪切过程中，研究了非饱和土与结构之间的微观力学剪切特性，包括颗粒位移、接触力的大小和方向、毛细管力的大小和方向。随着吸力的增加，毛细管内聚力对界面宏观和微观力学行为的影响非单调变化。与毛细管或摆动模式相比，在索道模式下具有吸力（或饱和度）的样品通常显示出更明显的毛细管内聚效应。毛细管内聚力对非饱和土-结构界面行为的影响随着正应力的增加而减弱。