Alteration Under Wet/Dry Cycles of a Carbonated Clay-Rich Soil from Azazga Landslide Site

The weathering of rocks, especially the clay-rich rocks submitted to chemical attack or wet/dry cycles, may impact negatively the slopes stability. This study aims to characterize the alteration of a carbonated clay-rich material assimilated to a marl after the infiltration of polluted water as observed on Azazga site (Algeria) identified as a landslide area. The marl alteration was simulated in laboratory by wet/dry cycles and the level of material degradation was estimated using geotechnical tests (direct shear tests and fragmentation test) as well as physico-chemical measurements and microstructural observations by X-ray diffraction, mercury intrusion porosimetry, chemical analysis and scanning electron microscopy. The effect of wet/dry cycles with artificially polluted water was compared to cycles without pollutants. The tested carbonated clay-rich material composed by around 30.6% of quartz, 12.5% of carbonates and 45.1% of clays showed a higher degradation in contact with polluted water considered as an activator of the degradation. The soil porosity was evaluated with wet /dry cycles and it was estimated from 19.2 to 25% after the cycles. The degradability test (fragmentation test) agreed with the shear test results with a decrease of the cohesion c’ from 49.9 to 31.5 kPa (while the friction angle remained close to 20°). Results were confirmed at micro scale with few mineralogical changes and with a higher particle aggregation in presence of pollutants resulting in rough surface while a microporosity around 30 μm appeared after cycles with or without pollutants, probably between disaggregated elongated grains or staked plans observed by SEM. In conclusions, wet/dry cycles with water (without pollutant) were mainly responsible to the disaggregation of carbonated clay-rich soil and pollutants reinforced such effect.