## 5 Conclusions  
In this work, four types of soil from French Guiana were analysed. The different soils have different chemical and mechanical characteristics. They come from four different geological horizons. Their main defects lie in their sensitivity to water. The latter is judged with simple tests such as MBV, particle size analysis, Atterberg limits, and sedimentometry, based on clay activity. As the materials are mainly silty, the activity of the clays is low, and their sensitivity to water is average. The chemical analysis of the soils highlights their alteration by the presence of iron and aluminium oxides characteristic of tropical soils.  
As it stands, the techniques used are not suitable for the direct use of these soils as a base course layer. Constructive measures, other than a simple two-layer overlay, must be taken to guarantee the waterproofing of the pavement during rainy season episodes.  
Through the study of the four different materials, it was shown that although the two soils BE42 and Cabale have identical classification according to the GTR (A2), their behaviour is different. Indeed, the Cabale soil has superior mechanical characteristics to those of BE42 in unconfined compression, making it more suitable for supporting vehicle traffic.  
Finally, the GTR classification alone does not allow the dissociation of two soils with very similar grain sizes.  
On the other hand, the use of chemical and mineralogical tests (CEC, MBV, granulometric analysis by laser diffraction, analysis by mid-infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy (ESEM + EDX)) provides an improvement in the GTR classification of the various soils by classifying the materials based on criteria other than particle size and clay content. In particular, it allowed a better separation of the BE42 and Cabale soils, which differ in their iron oxide content, which explains their different behaviour. In French Guiana, where laterite materials are used without any regulatory framework, the use of chemical and mineralogical tests could, as a complement to the GTR, enable better selection of laterite soils in order to assign them the best conditions for reuse. To complete this study, which combines the microscopic and macroscopic aspects of Guyanese clay soils, it is necessary to subject other laterite samples to these tests in order to verify the first hypotheses and thus create a database specifically for the Amazonian laterite. On the other hand, the use of the MCT (Miniature, Compacted, Tropical classification) methodology, used by our Brazilian neighbours, could make it possible to classify materials on the basis of criteria other than particle size and clay content. According to this new classification, it is possible to envisage methods of usingmaterials according to their characteristics and, in particular, their resistance to water based on the loss of mass by immersion tests.  
Conceptualisation, O.N.-R. and F.G.; methodology, F.G. and Y.E.; formal analysis, O.N.-R., F.G., Y.E., J.G., G.M., D.D. and C.M.; data curation, O.N.-R., F.G., Y.E. and J.G.; writing--original draft preparation, F.G.; writing--review and editing, O.N.-R., F.G., Y.E., J.G., G.M., D.D. and C.M.; supervision, D.D. and C.M.; funding acquisition, O.N.-R. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the European Regional Development Fund (ERDF) and the fund managed by company EIFFAGE INFRA Guyane(FEDER/2018/212/GY0016677). This work has benefited from an \"Investissement d'Avenir\" grant managed by Agence Nationale de la Recherche (CEBA, ref. ANR-10-LABX-25-01).  
Not applicable.  
The authors declare no conflict of interest.