Macro- and meso-scale mechanisms of geosynthetics in mitigating frost heave under coupled temperature, moisture, and dynamic loading: A combined OFDR and CT study

To investigate the deterioration of subgrade soils under combined temperature, moisture, and dynamic loading, one-dimensional column tests were performed with an open water supply. Five configurations were compared: unreinforced control, nonwoven geotextile, woven geotextile, bidirectional geogrid, and triaxial geogrid. Optical frequency domain reflectometry (OFDR) and X-ray computed tomography (CT) were jointly employed to monitor temperature and fiber strain fields and to characterize the residual pore structure after testing. The OFDR measurements indicated that, in the tested specimens, the triaxial geogrid maintained the most uniform fiber strain distribution, with its strain range being approximately 45% lower than that of the nonwoven geotextile under the lower dynamic load. In the unfrozen zone, the triaxial geogrid specimen exhibited the lowest macroporosity (20.7%) and the smallest average equivalent pore diameter (77 µm) among all reinforced specimens, while the geotextile groups exhibited higher porosity and connected crack networks. Under higher dynamic loading, total frost heave decreased across all groups, with the NW group remaining the smallest, but the strain fields became less uniform . These multiscale observations suggest that geotextiles mainly act as hydraulic barriers that limit ice lens growth in the frozen zone, whereas geogrids function as stiffening skeletons that homogenize deformation and preserve pore structure in the unfrozen zone. The combined use of OFDR and CT proves effective in capturing mesoscale structural signatures that macroscopic measurements alone cannot provide, thus offering new insights into the distinct reinforcement mechanisms under coupled loading and freezing conditions.