The mechanical behavior of the geogrid-soil interface is a key factor governing the stability and bearing capacity of reinforced soil structures. Large-scale direct shear tests and discrete element method (DEM) simulations were conducted to investigate the shear characteristics of geogrid-soil interfaces with different transverse rib thicknesses, and a nonlinear predictive model for passive lateral resistance was established based on the experimental results. The results indicated that enhanced transverse ribs significantly increased the peak shear stress of the interface, although all interfaces still exhibited shear-softening behavior. With increasing transverse rib thickness, the mechanical interlocking between particles was strengthened, and the interface cohesion and internal friction angle increased to 2.20 and 1.34 times those of the planar geogrid, respectively. Under cyclic shear loading, increased transverse rib thickness elevated the cyclic peak shear stress, reduced the hysteresis loop area, and suppressed the progressive accumulation of plastic deformation. In addition, successive loading cycles led to a progressive increase in interface shear strength, and the strengthening rate was positively correlated with the transverse rib thickness. Compared with planar geogrids, the 11 mm transverse rib configuration exhibited a higher force-chain density within the soil, a 16.7 % increase in the average particle coordination number, and a 275 % increase in shear-band thickness at a shear displacement of 50 mm. The results revealed that transverse rib thickness improved the shear performance of the geogrid-soil interface by enhancing passive lateral resistance, particle interlocking, and force-chain transmission, providing a theoretical basis for the structural optimization and engineering application of three-dimensional geogrids.