Experimental studies on the cyclic behaviour of reinforced unbound railway base courses

In railway construction, base courses of unbound coarse-grained material are usually placed between the existing subgrade and the track. Geosynthetics, in particular geogrids, are used to improve the system behaviour. The reduction in the thickness of the base course due to the geogrid is based on empirical approaches. In this work triaxial tests were performed to investigate the influence of the geogrid. A specimen size of d · h = 100 · 200 mm was chosen. This small sample size saved material, reduced workload and allowed the use of a standard triaxial apparatus. However, the base course material and the geogrid had to be geometrically scaled. Cyclic triaxial tests were carried out on the unreinforced and reinforced specimens with the aim to reproduce the conditions caused by rail traffic loading. For this purpose, the low stress and high number of loading cycles N = 500,000 were chosen. It was shown that the inserted geogrid reduces the magnitude of deformation and the accumulated strains compared to the unreinforced material.