A Study on CBR of Railway Track Foundations with Geosynthetic Reinforcement

Several series of laboratory California bearing ratio (CBR) tests have been conducted to evaluate the influence of geosynthetics on load bearing behaviour of railway track formations over clay subgrade. The effects of subgrade strength, subballast thickness, placement depth of geogrid reinforcement, number of geogrid layers and geotextile at subballast base have been brought out. With a layer of geogrid in the subballast, the increase in bearing resistance and stiffness of the track bed can be as high as 115% and 83% in case of strong subgrade and 97% and 61% for weak subgrade, respectively. An additional increase in CBR due to four layers of geogrid can be as high as 35% and 59%, for strong and weak subgrade condition, respectively. The CBR test parameters were correlated with the plate load tests parameters, through regression analysis. The obtained equations are found to be reasonably good in predicting the subgrade modulus and the strain modulus values of the track beds.