Assessment of deformation variation of pile-treated loess subgrade using nondestructive testing

The road subgrade filled with compacted collapsible loess is prone to becoming loose and porous, leading to uneven deformation and pavement distress. In order to address this issue, this study utilized High Pressure Jet Grouting Pile (HPP) and Dry Mix Gravel Pile (DMP) to reinforce the loess subgrade. Nondestructive detection methods, such as elevation observation, Raleigh-surface-wave testing, and ground penetrating radar (GPR) were conducted on an on-site embankment to evaluate the accumulated deformation rate (<i>r_a</i>) and compactness (<i>c_d</i>) of the treated subgrade. The results demonstrate that HPP and DMP effectively reduce collapsible deformation and enhance the strength of the loess subgrade. Specifically, the observation results reveal that the ra decreased to less than 5 mm per month, compared to the 20 mm per month before treatment. Moreover, the velocity of the treated embankment significantly increased, indicating that the HPP and DMP piles improved the density of the subgrade, leading to enhanced compactness (<i>c_d</i>). It was observed that the subgrade deformation no longer accumulated rapidly when <i>r_a</i> was below 5 mm per month or when the Rayleigh-surface-wave velocity was less than 150 m/s. Additionally, the application of on-site elevation observation and Raleigh-surface-wave testing proved to be quick and reliable in evaluating the deformation and compactness of the loess subgrade.