Comparative evaluation of particle movement in a ballast track structure stabilized with biaxial and multiaxial geogrids

Geogrids usually are used in railroad track substructure for ballast reinforcement and stabilization over a weak subgrade. Different aperture shapes affect the confining effect on ballast particles due to the unique interlocking mechanism. To understand the effect of aperture shape on ballast particle movement and the associated interlocking mechanism, three types of ballast box tests were conducted: one without geogrid as a control, one with a layer of biaxial geogrid, and one with a layer of multiaxial geogrid. If a geogrid was included, the geogrid was placed 30 cm below the top of the ballast. 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 known as SmartRocks were embedded under the rail seat and under the shoulder at the ballast-subballast and subballast-subgrade interfaces. Results indicate that the multiaxial geogrid significantly decreased accumulated vertical displacement in the ballast surface under cyclic loading and has the best potential for confining particle movement. The advantages of having a layer of multiaxial geogrid, including reducing particle movement, as well as decreasing vertical displacement of the ballast surface, are discussed.