Geosynthetics in the form of geotextiles and geogrids made of polymeric materials are being used to improve the bearing capacity of railway trackbeds. These materials provide a confinement effect through friction. In the same manner, geocells refer to a synthetic, honeycomblike cellular material, the structure of which is interconnected by joints to form a cellular network used for the confinement of soils. A literature survey reveals that the introduction of a 200-mm-high geocell into the upper subgrade layer increases the resilient modulus of this reinforced layer by an average multiplier factor, termed MIF (Modulus Improvement Factor), of 2.5. The MIF is supported both by in-situ FWD and by pressure-cell testing. Empirical calculations, furthermore, indicate that MIF is a function of the properties of the geocell. Thus, this reinforced layer can be regarded as part of a railway trackbed structure. Given these findings, the paper suggests the use of an equivalency procedure in order to calculate the effective thickness of a 200-mm reinforced subgrade layer in terms of the thickness of type A (CBR=60%) sub-base material in railway trackbed structures. For example, when a given subgrade with a CBR value of 10% is reinforced by the 200-mm height of a high-standard geocell, this reinforced subgrade can substitute for a 150-mm type A sub-base layer. Finally, it should be pointed out that (a) the proposed equivalency procedure is valid for a subgrade CBR of up to 12%, and (b) the use of geocell reinforcement should be accompanied by a strictly detailed QA plan for in-situ density and modulus (plate-load testing) of the reinforced layer.

CBR; confinement; equivalency factor; geocell; Modulus Improvement Factor (MIF); Railway trackbed; resilient modulus