## 1 Introduction  
French Guiana has an equatorial climate with two climatic seasons: a dry season and a wet season. Similar to most countries in the inter-tropical zone, it has large resources in terms of lateritic materials which are commonly used for the construction of road infrastructure (forest roads, unpaved tracks, etc.). According to the National Office of Forests and the SAR (Schema d'Amenagement Regional), 73% of Guyana's road network consists of unpaved rural roads [1]. The alternation of the seasons induces cycles of shrinkage/swelling on these more or less claye soils and consequently favouring their variation in volume. The main defect of these lateritic materials lies in their characteristics, in terms of fineness and plasticity. They are particularly sensitive to water. Several studies based on laboratory tests have been carried out to define the physical and mechanical characteristics that gravel materials should have for use in road construction [2; 3; 4; 5]. According to [6], lateritic gravels with aggregate crushing and LA abrasion values of less than 30% and 34%, respectively, and 10%of fines can be used satisfactorily for pavement construction on heavily trafficked roads. [PERSON] [7] observed on roads made in Kenya that the laterites had high plasticity index (7-21%), wide ranging of laboratory soaked CBRs (12-96% at 95% BS compaction), and 14-49% of rock fractions finer than 0.063 mm. Other studies in other tropical countries use the criteria based on the Afterberg limits and grain size distribution. [PERSON] et al. [8] discuss the wide range of specifications for lateritic soils and highlight the diversity of soils selection criteria for road construction. To better understand the behaviour of these materials, other macroscopic analyses can allow a better classification of the soils present in the intertropical domain. In Brazil, a classification methodology for tropical soils, the MCT classification (Miniature, Compacted, Tropical) [9; 10], classifies soils according to criteria other than granulometry and clay content while presenting conditions for the soil reuse in road infrastructure. In most of these studies, no chemical analysis is considered. However, some work has shown that mineralogical constituents and microstructure have a significant influence on the geotechnical properties of lateritic soils [11; 12]. The mode of formation and the mineralogical composition of the bedrock determine soil cohesion and compressibility characteristics [13]. It is therefore clear that the mechanical and geotechnical characteristics of lateritic soils are variable depending on the local conditions. Research in Brazil, notably by [PERSON] et al. [14], shows the example of a section of a road in the state of Amazonas that deteriorated after a short period of use. They noted that this disorder was not due to a structural design problem but to the interaction between the soil and the atmosphere. There are also many typical examples in French Guiana where cracks are generated in particular by the swelling of the soil in the rainy season. The swelling character of these soils is related to the amount and types of clay minerals present. Indeed, the amount of clay minerals and more particularly those of the smectite type contribute to the swelling phenomenon [15; 16]. Thus, identifying and evaluating the potential of lateritic soils for the use in road construction based on their geotechnical properties alone, as recommended by the French standards [17; 18], may be misleading given the evolving nature of these soils. Laterite soils may be different and may also behave differently depending on the paedogenic factors [19; 20]. Despite the numerous studies carried out on the soils used in road construction, there are no scientific studies on the geotechnical characteristics of the lateritic soils of Guiana. In this paper, the physical, geotechnical, chemical, and mineralogical characteristics of four tropical soils from French Guiana are studied for their use in road construction.