Assessing compaction of existing railway subgrades using dynamic cone penetration testing

Dynamic cone penetration testing has been extensively used in the past for subgrade performance assessment and quality control in road construction practice. However, the method is not commonly employed on high-speed railways. This is due to lack of field data that prove its feasibility as an alternative method for assessing subgrade quality. To mitigate this gap, a series of in situ tests was performed on existing subgrades built with coarse-grained soils at five different sections along the Tehran-Isfahan high-speed railway in Iran. At each subgrade section tested, four parameters for compaction quality control - blow count, degree of compaction, subgrade reaction modulus and dynamic deformation modulus - were determined at nine different depths from subgrade surface. On the basis of the results obtained, a correlation model was developed to relate the traditional quality control parameters of compacted subgrade fill materials with the blow counts. Finally, a simple method using the correlation models established was proposed for assessment of subgrade compaction quality. The method proposed proved to be an alternative approach for evaluating the state of subgrade compaction and also for assessing the subgrade performance of existing railway subgrades.