Macro and meso-scale evaluation of expansive soil-geogrids interaction: mechanical properties and PIVLAB-based mechanism analysis

The geogrid-soil interaction mechanism is a critical factor governing the stability of geogrid-reinforced roadbed. To evaluate the macro-mechanical behavior and underlying mechanisms at the interface between geogrids and expansive soil, a series of large-scale pullout tests were conducted. Digital image correlation (DIC) and particle image velocimetry (PIVLAB) techniques were employed to analyze the movement patterns of soil particles and the development of shear zones. A prediction model for pullout resistance, considering multiple influencing factors was established, and the predicted values were in good agreement with the experimental values. The results revealed that: Macroscopically, the geogrid pullout resistance-displacement curve exhibited a strain softening behavior. The interfacial cohesion and friction angle of biaxial geogrids were significantly greater than those of uniaxial geogrids, increasing by 60.8% and 21.7% respectively. The interfacial friction coefficient was consistent with the power function model with the increase of normal stress. Mechanistically, the motion vectors of soil particles above and below the transverse ribs were asymmetric, with the displacement of soil particles above being greater than that below. The thickness of the shear band was notably affected by the normal stress and geogrids type. This study elucidated the movement patterns of soil particles at the soil-geogrids interface and the formation of shear zones, and proposed a predictive model for pullout resistance. These findings provide important theoretical support for application of geotechnical engineering in transportation.