# Comparison of Field and Laboratory Tests for Soil Suitability Assessment in Raw Earth Construction
## 1 Introduction
Adobe is a raw earth brick shaped by hand or in a wooden mold in a plastic state and air-dried, with clay/ silt content between 5 and 70% [20]. CEBs are obtained by compressing earth containing 0-40% gravel, 25-80% sand, 10-25% silt, and 8-30% clay in presses [21]. Poured earth [22], often referred to as wet earth construction, involves mixing earth with enough water to achieve a fluid consistency that can be poured into formwork, much like concrete. This method typically requires soil with a clay-sized particle content ranging from 5 to 20%. Achieving the right flowability is important, and controlling the water content carefully helps to minimize the risk of shrinkage cracks as the mixture dries [23]. The water content for poured earth is generally higher than what's used in rammed earth, usually sitting between 25 and 40%, depending on the specific soil composition. On another note, earth plasters are one of the oldest surface finishing techniques still in use today. They serve both protective and esthetic purposes for earth buildings. These plasters are made by mixing clay-rich soil, which typically contains about 10-30% clay, with sand, and sometimes adding organic fibers or other materials to help prevent cracking [24; 25]. The proportions can vary based on the application and environmental factors. Research has shown that earth plasters can significantly contribute to indoor humidity regulation due to their hygroscopic properties. Recent studies have also highlighted that the characteristics of the soil, especially its clay-sized particle content and mineral composition, have a strong impact on key properties of the plaster, such as how it shrinks, its adhesion strength, and its overall durability. Depending on the type of application, the addition of plant aggregates and fibers is also possible, thus modifying their mechanical, hygothermal, and durability properties [26; 27]. The suitability of soil for earth construction hinges on several important properties that significantly affect how the material performs. Key parameters to consider include particle size distribution, plasticity characteristics, clay-sized particle content, and activity, as well as organic matter (OM) content. Various guidelines and studies indicate that suitable soils typically have a clay-sized particle content between 5 and 30%, although the exact range can vary depending on the specific construction technique used [21; 28]. Clay-sized particle content and mineralogy are vital since they offer cohesion and impact how the material interacts with water [25]. The plasticity index (PI) is an important measure, indicating the range of water content where the soil displays a plastic behavior; for most earth construction techniques, this should generally fall between 5-30%. It is also advised that OM content remains under 2-4% to prevent decreased mechanical resistance and excessive shrinkage [29]. Additionally, the grain size granulometry of the soil plays a crucial role in determining its compactability and final density, with well-graded soils often preferred for optimal particle packing. Recent research has uncovered links between these fundamental properties and the overall performance of the material. For instance, clay activity, measured by the Methylene Blue Value (MBV), can correlate with material strength [29], while plasticity characteristics can influence shrinkage behavior with higher plasticity indices typically leading to an increased shrinkage potential and susceptibility to cracking [30]. Furthermore, the distribution of particle sizes impacts both mechanical and hygrothermal properties [18]. Furthermore, [PERSON] and [PERSON] [25] demonstrated that cation exchange capacity correlates with volume stability and durability, while [31] established important correlations between the clay mineral content and hygrothermal properties, particularly the moisture buffering capacity.