A railroad ballast or subballast layer is composed of unbound granular particles. The ballast/subballast initial compaction phase occurs immediately the construction or maintenance of a track structure is finished. The particles are densified into a more compact state after certain load repetitions. Geogrids are commonly used in railroad construction for reinforcement and stabilization. Currently heavy haul trains are increasing the loads experienced by the substructural layers, which changes behavior of reinforced granular particles. This paper presents a series of ballast box tests to investigate the behavior of geogrid-reinforced unbound granular particles with rectangular (BX) and triangular (TX) shaped geogrids during the compaction phase. Three types of tests were conducted: one without geogrid as a control, one with a sheet of rectangular shaped geogrid, and the other one with a sheet of triangular shaped geogrid. The geogrid was placed at the interface between subballast and subgrade layers. A half section of a railroad track structure consisting of two crossties, a rail, ballast, subballast and subgrade was constructed in a ballast box. Four wireless devices-"SmartRocks", embedded underneath the rail seat and underneath the shoulder at the interface of ballast-subballast, and subballast-subgrade layers, respectively, to monitor particle movement under cyclic loading. The behavior of the unbound aggregates in the three sections under two different loading configurations were compared. The results indicated that the inclusion of the geogrid significantly decreased accumulated vertical displacement on the ballast surface, ballast particle translation and rotation under a given repeated loading configuration. The results also demonstrated the effectiveness of the SmartRock device and its potential for monitoring behavior of ballast particles in the field.