Compression and wetting induced volumetric behavior of loess: Macro- and micro-investigations

Volumetric behavior of intact and compacted loess under isotropic compression and wetting was investigated through stress- and suction-controlled triaxial tests. To assist in the interpretation of test results, X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Mercury Intrusion Porosimeter (MIP) tests were carried out to determine the mineral composition and the microstructure of the tested loess. Results of compression tests showed that yield stresses of intact loess were larger than that of the compacted loess because of stabilization effects contributed by clay particles and calcite in intact loess, as evidenced by SEM and XRD results. On the other hand, constant water content was observed for intact loess during compression at suctions 50 kPa and 100 kPa, while the water content of compacted loess increased by 4.4% and 7.4% respectively. MIP tests revealed that compression of the intact loess mainly occurred in the extra-large pores, but with minuscule effects on the pores governing water distribution at suctions 50 kPa and 100 kPa. For compacted loess, a number of inter-aggregate pores were compressed below the pore diameters responsible for water flowing in the pores at the applied suctions. In addition, intact loess showed wetting induced swelling at an isotropic stress of 50 kPa, while collapse was observed for compacted loess with the same stress path.