Peloid is a natural product developed during the maturation process between a clay material and water and is used in health and wellness centres due to its mineralogical, physiochemical and biological properties. However, the potential therapeutic value of clays in Portugal has not been fully investigated. Therefore, the main objective of this research is to identify the effects of two mineralized waters: thermo-mineral water (sulphurous and hydroxylated water abundant in chloride ions, sodium and calcium) and seawater, on three residual soils from Alentejo, from a morphological, mineralogical and chemical perspective. The peloids morphology is more homogeneous than the residual soils, and the particle size decreases during the maturation process. Thermo-mineral water enriched the peloids in smectite (58-76 %), while seawater newly formed Na-minerals (decreasing smectite contents to 39-54 %). Smectite is essentially montmorillonite, although there is nontronite and beidelite. The residual soils and peloids have a silicilastic composition (32.23-52.85 %), between 14.22 and 20.53 % of Al2O3, and besides smectite, the mineralogical composition is composed of salts (only in seawater peloids), feldspars, iron oxides, carbonates, and quartz. Morphology and mineralogy enhance the influence of waters in peloids properties and suggest that this samples have potential therapeutic value. Furthermore, physicalchemical, rheological, thermal and biological analysis are needed to support these findings.

Desiccation crack patterns are commonly observed in natural and engineered soils and provides preferential pathways for moisture infiltrating into the soil. Cracks occur easily in soil when moisture is lost due to desiccation. Crack formation and development are closely related to moisture content and have a marked impact on the soil deformation characteristics and hydraulic properties. However, the critical moisture content below which desiccation cracks appear in the soil is usually determined by experiment because there is a lack of research on theoretical calculation models. Therefore, a theoretical calculation model is proposed to calculate the critical moisture content, and a parameter, lambda\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda$$\end{document}, based on the following relationships: between soil grain size and suction, between suction and tensile strength, and between soil cracking and tensile strength. The critical moisture content values of different grain compositions were calculated and compared with laboratory experiments of desiccation crack. The critical moisture content of the granite residual soil is between 20% (50% liquid limit) and 30% (75% liquid limit). The presented model provides a means to estimate the critical moisture content of crack formation from soil desiccation using basic soil properties. This method can estimate the characteristics of soil desiccation cracks under extreme weather condition.

The geotechnical characterization of residual soils is a complex matter and is not always successful because current interpretation methodologies dedicated to sedimentary soils do not adequately respond to the behavior of this type of soils. The problem has been under scope by several Portuguese and international institutions. The work carried out in the experimental Site of the Polytechnic Institute of Guarda (IPG) since 2003, constituted by residual soils and decomposed rocks of the local granite massif, is highlighted herein. The work was strongly supported by MOTA-ENGIL (Portuguese construction company) and the Laboratory of Math Engineering (LEMA, Polytechnic Institute of Porto). The characterization of the test site and the respective research work is presented. The research work involved interpretation of in situ tests (SDMT, SCPTu, PMT, SPT, DPSH, and geophysical tests), tests in controlled chambers (DMT, geophysical, and suction tests), and laboratory tests (oedometric tests, direct shear tests, and triaxial tests with several stress paths). The tests were performed on natural structured soils, artificially cemented mixtures, and unstructured soils. Advanced math and statistical analysis were applied in the development of new correlations to obtain geotechnical parameters representative of these soils. Furthermore, the work also allowed to recognize the physical characteristics of the materials and better understand their mechanical behavior.

Infrastructure projects on slopes that are exposed to changes in water levels face unique challenges. Fluctuations in water levels can significantly impact the stability and integrity of the slope. Stresses affecting soil nails are influenced by various factors, including changes in groundwater levels due to rainfall, temperature variations, or human activities. While studies have addressed the use of soil nails to enhance slope stability, there has been limited attention to the performance and serviceability of soil nails under cyclic changes in the groundwater table. Lateritic slopes are susceptible to instability due to factors such as extensive weathering, inadequate drainage, and steep cuts. Erosion and slope failure are exacerbated by insufficient vegetation cover, climate-induced degradation, and human activities. This highlights the importance of understanding the stress generated and the interaction between the soil and reinforcing material. In this study, centrifuge modelling was employed to simulate cyclic saturation and desaturation of a lateritic slope in response to fluctuations in groundwater levels. Four centrifuge tests were conducted on slopes with a 5V:1H ratio, both unreinforced and reinforced, at two different soil densities. The slopes were subjected to cycles of saturation and desaturation using a seepage simulator located behind them. Both unreinforced and reinforced slopes exhibited stability within a gravitational range from 1 to 40 g, showing no apparent cracks or settlements. Following the initiation of water flow through the slope, a gradual flow slide failure occurred in the unreinforced slope. When exposed to fluctuating water levels, the utilization of soil nails prevented the development of a continuous slip plane in higher-density slopes, while lower-density modelling revealed a failure slump and tensile cracks on the slope surface. Increased excess pore water pressure during ground saturation reduced effective stress on soil nails, reducing their tensile resistance. Conversely, lowering groundwater levels increased effective stress, mobilizing axial forces in the nails. This cyclic variation caused visible changes in settlements, strains, and tensile cracks in the slope following saturation and desaturation cycles.

A review analysis of a database of 237 small strain stiffness measurements performed on 35 different residual soils is presented. The reinterpretation of the tests was conducted with respect to the loading conditions and physicochemical parameters published in the literature. Besides, the database was completed with the results of a case study from a dam construction project in the French West Indies. On the basis of a detailed and carefully justified analysis, parameters influencing the response of saturated residual soils to small strains are identified, is proposed. The correlations between the identification characteristics of the residual soils (initial void ratio, Atterberg limits, clay fraction) and the model parameters are investigated. The article proposes a general model for the evaluation of the small-strain stiffness of saturated residual soils using, in addition to the mean effective stress (p') and the maximum mean effective stress (p'max) the initial void ratio (e0) and, for intact soils, the clay fraction (CF) or, for remoulded soils, the plasticity index (PI).

The mechanisms of soil failure on a microscopic scale are still not fully understood. Many soil behaviour models characterize a soil failure at the macroscopic level as single, continuous plane. Although on a microscopic scale, failure planes have a complex structure and are considered shear zones. This work aims to contribute to the microscopic analysis of the shear zones in residual soils. It describes the structures observed at the shear zones and correlates the microstructures to the macroscopic behaviour of a gneiss residual soil. The analyses interconnect the microscopic view with the stress-strain behaviour, stress path, and critical state line of the tested soil. The studied shear zone was generated in a laboratory during CAU triaxial tests. Images were obtained using a backscattered electron detector in a scanning electron microscope and subsequently subjected to digital image analysis. The variation in porosity and the degree of alignment of grains and lumps along the shear zones were evaluated. Smaller shear zones that make up a larger shear zone were also found. From the results, it was concluded that there is a strong influence of the strain level and effective confining stresses on the structure and geometry of the shear zones.