# Comparison of Field and Laboratory Tests for Soil Suitability Assessment in Raw Earth Construction
## 1 Introduction  
At a time when modern construction resources are no longer viable in terms of energy consumption, resource depletion, and greenhouse gas emissions, rethinking the act of construction has become urgent [1, 2]. Conventional building materials such as cement concrete and steel can no longer be used massively and by default, must be replaced, where possible, by more sustainable, resilient, and decarbonized alternatives [3, 4, 5]. Rawearth is one of the ideal candidates for this paradigm shift. Earth construction not only offers environmental advantages but also embodies a deep-rooted cultural heritage, especially in areas rich in clay soils. Traditional earthen structures are key components of the architectural identity in numerous regions, reflecting the skills and techniques that have been handed down through generations of skilled builders. The methods employed in these traditional practices, such as selecting and preparing soil, represent invaluable knowledge that enriches modern scientific approaches. It is essential to preserve and study these techniques, particularly for the maintenance and restoration of historic buildings. Gaining insight into these age-old construction methods and their material choices assists in developing effective conservation strategies, ensuring that these structures remain a lasting symbol of sustainable construction [6]. In general, earth is abundant, and it is the main waste of the construction and public works industry, making it widely available and accessible. The soil used for earth construction is inorganic soil, typically found beneath the organic topsoil used for agriculture. Earth materials also provide interesting acoustic and hygrothermal properties due to their moisture-thermal buffering abilities that complement bio-based materials [7; 8; 9; 10]. It can add thermal inertia to buildings, helping to address the summer comfort challenges posed by climate change [11]. [PERSON] et al. [12] and [PERSON] et al. [13] demonstrated the passive CO\({}_{2}\) regulation capacity of the indoor air of earth construction. In addition, earth is part of a circular approach since it can return grounded after use, or be repaired and then reused endlessly, simply by rehumidifying. Earth construction provides a technical solution that addresses environmental, health, and social challenges in contemporary building practices [14; 15]. Since soil is a local resource found almost everywhere, its properties can vary significantly. The subsoil geology can differ widely, and the soil extracted may not always be suitable for every construction project. The CRATerre technology wheel effectively illustrates the diversity of earth applications in construction [16]. In the literature on raw earth, its various forms are generally categorized into several main techniques, including rammed earth, cob, adobe, compressed earth blocks (CEBs), extruded earth bricks, mortar, lightened earth, poured earth, and coatings. The rammed earth technique consists of compacting moist earth, i.e., between dry and plastic, in several layers within a formwork, with a thickness greater than or equal to 50 cm, allowing for the construction of massive and monolithic walls [17]. For this type of construction, the clay-sized particle content is between 5 and 30% to ensure the bonding of the soil grains, while limiting the risk of shrinkage [18]. This optimal water content varies according to the soil and allows it to reach the maximum density for a given compaction energy [18]. Wattle and daub is a load-bearing wooden structure filled with a sticky clay-rich soil mixture containing sand and plant fibers to prevent cracking of the mixture during drying, with the addition of water to obtain a plastic material [19]. Cob is also made from plastic state raw earth mixed with fibers (straw or other local plant fibers) and is used to build monolithic and load-bearing walls. A typical mixture of Cob consists of about 30% gravel, 35% sand, and 35% silt and clay, with a variation of \(\pm\)10% [14].