Earth concrete is composed of fine particles which make them very sensitive to humidity and affects their longterm durability. In this study, the effect of wetting/drying cycles on earth concrete according to ASTM D559 was studied by measuring the weight loss, pH, and Electrical Conductivity (EC). The effect of different percentages of flax fibers was investigated. The residual properties of reference specimens and earth concrete specimens subjected to wetting/drying cycles were evaluated by conducting compressive tests at the end of the 25 cycles. Ultrasound, Acoustic Emission (AE), and Digital Image Correlation (DIC) techniques were applied to estimate the concrete progressive deterioration during and at the end of the 25 wetting/drying cycles. The results showed that earth concrete degradation begins during the first cycle with visible cracks on the surface of the specimens. The mechanical tests showed a considerable loss of earth concrete mechanical properties after 25 cycles. The ultrasonic test showed that the degradation rate was more important for specimens without flax fibers. The cumulative acoustic activity was effectively used to assess the different damage progression phases and crack propagation. The signal parameters (energy, amplitude, etc.) evolution indicates premature damage for earth concrete specimens subjected to wetting drying cycles.

Stiffness of soil at very small strains G0 is mainly affected by void ratio, effective stress and suction. Empirical equations considering those factors have been proposed to estimate G0. However, for collapsible soil like loess, variations in suction might induce changes in void ratio of soil. The combined effect of these two factors poses challenges in accurately estimating of G0. This paper first presents an experimental study on the G0 of collapsible loess under various conditions, including as-compacted states, wetting/drying and K0 loading. G0 is estimated from shear wave velocity obtained with bender element technique. The changes of G0 with respect to void ratio, suction, effective stress, and wetting under K0 stress conditions are evaluated. Test results reveal that power relationships can be defined between G0 and void ratio, suction and effective stress, respectively. The changes in G0 along wetting/drying shows an S shape due to the different dominant effects on soil structure, as well as the induced non-uniform volume changes when suction change at different zones. Under K0 loading, G0 decreases upon wetting at stresses below the compaction stress, while it increases upon wetting at stresses above the compaction stress, due to the combined effects of densification caused by volume collapse during wetting and softening induced by suction decrease. Finally, a G0 model considering net stress and suction as independent stress variable is proposed. This model could effectively capture the change of G0 during wetting, drying and loading, as well as upon wetting under K0 loading for collapsible loess.