Three-year site monitoring of a sea dike with lime-treated silty soil in southern France

With an increasing number of extreme climate events and continuous sea level rising, the durability and stability of dikes have become a sustained concern all over the world. In this study, one experimental sea dike built in Southern France, on four plots including three treated with lime and one untreated as a reference, was monitored over three years. The monitoring data include soil temperature, pore pressure, soil pH, soil suction, water salinity, and parameters related to the atmosphere. Based on the monitoring data, the thermal conductivity, soil water retention characteristics, and erosion resistance were analyzed and compared for different plots with different lime contents and compaction ratios. Results showed that the lime-treated plots clearly exhibit better stability than the untreated plot, and the degree of compaction seems to be more significant than lime addition in improving the mechanical performance. After three-year exposure to the atmosphere and cyclic wave loading, all of the four plots deteriorated more or less severely with surface erosion, which exposed the internal soil to the atmosphere and caused incremental variations in pore pressure and suction for the soil near seawater. The pH value of treated-soil started to decrease after nearly one year of monitoring, even with lime addition higher than the optimum lime content. It is thus essential to further investigate the appropriate lime dosage and degree of compaction to improve the surface erosion resistance of treated soils in sea-adjacent environment.