Strength and stiffness assessment of railway track substructures using crosshole-type dynamic cone penetrometer

To ensure safe train services, an effective method is required for the characterization of the strength and stiffness of railway track substructures. In this study, a crosshole-type dynamic cone penetrometer (CDP) is developed to characterize the strength by the crosshole-type dynamic cone penetration index (CDPI) and stiffness by the shear wave velocity (V_s). To verify the V_s obtained using the CDP test, the V_s obtained by both CDP and bender elements are compared in a chamber test. In addition, for the characterization of the railway track substructures, field tests are conducted. The chamber test shows that the V_s obtained using the CDP are almost the same as those obtained by bender elements. In field tests, the CDPI and the V_s are profiled along the depth, the including ballast, sub-ballast, and subgrade layers, which are identified by ground penetrating radar surveys. As the CDPI is highly correlated to the V_s, the stiffness characteristics are considered to be reasonable and can be simply estimated using the CDPI. This study demonstrates that the CDP test can be used for the evaluation of the strength characteristics and small strain elastic properties of the track substructures.