# Comparison of Field and Laboratory Tests for Soil Suitability Assessment in Raw Earth Construction
## 3 Results and Discussions
### Suitability Assessment
These correlations validate the complementarity between laboratory and field-testing methods. Notably, soils falling within recommended gradation envelopes for specific construction techniques do not necessarily satisfy both plasticity criteria and field test requirements. For example, soil 4-St Selves, despite having a suitable gradation curve for certain techniques, shows low plasticity (PI = 13.7%) and poor field test performance (cigar length 4.8 cm), suggesting that comprehensive testing across all methods is crucial for proper soil evaluation. The relationship between particle size distribution and plasticity is not strictly linear, as demonstrated by soils like 8-Haux, which shows moderate gradation but high plasticity and strong field test results (cigar length 15.7 cm), indicating that other factors such as clay mineralogy play significant roles. This three-way correlation between particle size distribution, plasticity characteristics, and field test results provides a more robust framework for evaluating soil suitability for earth construction, highlighting the importance of considering multiple parameters rather than relying on a single testing approach. The results of the GTR classification of soils do not coincide with the suitability of soils for raw earth construction. Two soils that are very different from the perspective of raw earth construction can have the same GTR classification (e.g., soil 1 and soil 10). Conversely, similar soils from the perspective of raw earth construction (e.g., earth 7 and 6) have different GTR classifications (A2 and B5). Therefore, the GTR classification does not allow for classifying soils based on suitability for raw earth construction. Figure 8: Relationships between PI and liquid limit and correspondence of soils to plasticity recommendations. The analysis of the 39 soils identified four distinct groups based on their unique properties and potential construction uses. Group A features soils with high clay content, represented by soils 1, 3, and 8, which have over 25% clay, a plasticity index (PI) above 30, cigar test lengths longer than 15 cm, and strong performance in ring tests, making them particularly suitable for applications such as adobe, cob, and earth plasters. Group B includes balanced mixed soils, represented by soils 5, 7, and 10, containing between 15 and 25% clay and a PI of 15-30, with cigar test lengths ranging from 7 to 15 cm and moderate ring test performance, demonstrating versatility ideal for rammed earth and CEBs. On the other hand, Group C consists of sandy soils, represented by soils 4, 6, and 9, which have less than 15% clay and a PI under 15, tend to perform poorly in both cigar and ring tests, and often need modification for most construction uses. Lastly, Group D encompasses soils with high organic content, including soils 2, 11, 38, and 39, which contain more than 4% OM and require treatment before use, regardless of other characteristics. These classifications provide a useful framework for selecting and modifying soil for construction, where Group A aligns well with traditional applications in plastering and adobe-making due to their favorable properties; Group B shows adaptability with consistent field assessments indicating suitability for various methods; Group C poses challenges for direct use but can often be enhanced with clay addition or stabilization techniques; and identifying Group D through basic field testing is crucial, as organic content significantly impacts construction properties, although precise measurement necessitates laboratory analysis. The development of a methodology for assessing the suitability of soils is proven to be complex. While the results of the field and laboratory tests provide relevant information for characterizing soils, the process of transforming the material into construction materials involves many additional parameters to consider. The characteristics of the tested soils can be modified upstream of the implementation, through a simple sieving process or the addition of sand.