# Comparison of Field and Laboratory Tests for Soil Suitability Assessment in Raw Earth Construction
## 3 Results and Discussions
### Laboratory Test Results
[64] reviewed six existing proposals of fine-grained soil classification systems and ranked them from highest to lowest suitability. Artificial intelligence in parallel with deep learning was also applied for soil classification [65]. In our study, the Guide des Terrassements Routiers (GTR) classification [66] which is frequently used by geotechnicalians is used. The GTR is a French soil classification system widely used in geotechnical engineering that categorizes soils based on their granulometric and state parameters. This later considered granulometric characteristics, Arterberg limits, and clay activity. 'A' classifications generally represent fine soils (with A1 indicating low plasticity, A2 medium plasticity, A3 high plasticity, and A4 very high plasticity), while 'B' classifications represent sandy and gravelly soils with fines (B5 indicating sandy soils and B6 gravelly soils). Figure 4 illustrates the relationship between OM content (blue bars, right axis in %) and density (red diamonds, left axis) for the 37 soils, with each soil classified according to the GTR system. The OM content is a crucial characteristic for determining whether the soil is suitable for raw earth construction. It should be relatively low to avoid reduced mechanical resistance, shrinkage due to the disappearance of this material, and the porosity created. [PERSON] et al. [21] recommend that the OM content not exceed between 2 and 4% in soils used for earth-based building materials to ensure material stability, durability, and performance. The OM percentage also influences other characterization parameters such as plasticity and blue value due to the ability of argilo-humic complexes to retain water, among other factors [67; 68]. However, the calcination test yields very different results from those predicted by the odor test in this study. Several soils have a very high OM content and must therefore be excluded or treated before use. The values from the calcination test are not substantially correlated to the visible presence of organic components or a humus odor. The data shows OM content varying significantly, from approximately 0.5% to 11%, with notable peaks in soils like 20-LaRochelle (\(\approx\)11%) and 21-Romegov (\(\approx\)7%). Most soils classified as A2 (medium plasticity fine soils) show relatively low OM content (2-4%). Density measurements remain relatively consistent, clustering between 2.4 and 2.9, suggesting no strong correlation between density and OM content. The predominance of A2 classification indicates that many soils in the study are fine-grained with medium plasticity, though the presence of B5 and B6 classifications indicates some variety in soil types. Notably, many soils exceed the recommended OM content limit for earth construction (2-4%), suggesting the potential need for treatment or modification before use in construction, despite their GTR classification. The density values presented in Figure 4 demonstrate relatively consistent measurements for the 37 soils, with values predominantly ranging between 2.4 and 2.9 g/cm\({}^{3}\). These values are typical for mineral soils and provide important insights into the material composition. The highest density values, approaching 2.9 g/cm\({}^{3}\), are observed in soils like 14-Etxegoinberri and 13-StPd'Irtube, suggesting a higher proportion of dense minerals in these soils. Conversely, lower density values around 2.4 g/cm\({}^{3}\), seen in soils such as 14-Etxegoinberri and 13-StPd'Irtube, suggesting a higher proportion of dense minerals in these soils. Figure 3: Soil plasticity classification based on the Atterberg Limits for the 39 studied soils. 21-Romegou and 30-GsurDropt, might indicate the presence of lighter minerals or OM. Interestingly, there appears to be no clear correlation between density values and GTR classification, suggesting that soil density alone is not a determining factor in the GTR system.