This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods.

This research focuses on soils derived from volcanic ash in the city of Popayan, stabilized with low percentages of cement. The results reveal high variability in properties due to changes in moisture content, structural condition, and curing time. The study involved evaluating the physical and mechanical properties in both natural state and after modification with cement at 3%, 4%, and 5%. Natural state soils exhibit deficient conditions, such as subgrades or embankments, necessitating improvement in various cases. When cement is used as a stabilizer, it is possible to conclude that there is an increase in mechanical strength and marginal improvements in hydraulic properties (cement- modified soil). However, these improvements are not comparable to the significant enhancements observed after reaching a 5% cement content (soil-cement).

Sustainable construction materials and local solutions are crucial for meeting urbanisation demands in tropical regions like French Guiana. Poured earthen construction, primarily composed of local soil, offers a cost-effective and environmentally friendly alternative. To ensure good consistency for pouring, the use of dispersants to deflocculate clay particles is an effective strategy that reduces water demand while enhancing the material's physical and mechanical properties. However, the variability of soil impacts the effectiveness of dispersants and the earth's material properties. It is currently unknown how the specific properties of tropical soils can influence the mix design of poured earth and how it impacts their resulting physical and mechanical characteristics. This work examines the soil properties that could help select suitable soil for poured earth construction. Four tropical soils of French Guiana were characterised in detail and used to prepare mortars with varying amounts of water and dispersant (sodium hexametaphosphate). The consistency and compressive strength of the mortars correlated with the mineralogical and geotechnical characteristics of the soils. In particular, soils with high levels of metal oxides produced mortars with the highest compressive strength. Using a dispersant consistently increased the compressive strength and dry density of the mortars and enabled a reduction in water content. Importantly, the analysis revealed that two easily measurable soil properties, the passing at 63 mu m and the pH measured in potassium chloride (pH KCl), could predict the mechanical properties of the mortars and the amount of dispersant needed. Specifically, the pH KCl correlated with the proportion of iron and aluminium oxide and showed a positive linear correlation with the compressive strength. Overall, this study identifies easily measurable soil properties, in particular the pH KCl, for selecting and designing high-performance earth materials with tropical soils. It offers promising prospects for industrialising poured earth construction.

With an increase in the generation of sewage sludge, there comes a demand for disposal methods for it, and agricultural use is a sustainable alternative. However, there are gaps regarding emerging pollutants, especially in the pharmaceutical class. Nimesulide - an anti-inflammatory pharmaceutical recently associated with liver damage and banned in some European countries - is among the most consumed pharmaceuticals in Brazil hence can be found in wastewater and, therefore, in sewage sludge used for agriculture at ng L-1 concentrations. The objective of this research was to evaluate the toxicity of the anti-inflammatory pharmaceutical nimesulide through toxicity tests using the organism Enchytraeus crypticus in both natural and artificial soils, adopting concentrations about studies carried out with other anti-inflammatory drugs on seeds in the soil. In this work, the toxicity of nimesulide was evaluated in natural tropical soil sampled in Sao Paulo - Brazil, and in tropical artificial soil. The invertebrate E. crypticus was exposed to nimesulide nominal concentrations of 200; 340; 578; 982 and 1670 mg nimesulide kg-1 of dry soil and the reproduction test was performed according to ISO 16.387 (2014) standard, with 5 replicates per concentration. The results obtained through reproduction testing with E. crypticus in each concentration presented were EC50 values of 699 and 759 mg nimesulide Kg-1 dry soil, respectively for both natural and artificial soil. The Tukey test showed no significant difference between the soils, however. Finally, this study suggests that the anti-inflammatory drug nimesulide displays a toxicological effect on the reproduction of soil fauna organisms in high concentrations. Therefore, stresses the importance of identifying and monitoring unknown concentrations of this emerging pollutant in the environment.