## 2 Materials and Methodology
### Sample Installation and the Direct Shear Test Procedure  
For the purposes of forming specimens, a cylindrical mold with a height of 300 mm and a diameter of 150 mm was used, inside which a smaller square mold for a specimen with dimensions of 100 \(\times\) 100 \(\times\) 20 mm was placed (Figure 6) on top of the already compacted soil layer. After placing the square mold, the mixture for the next layer was added and then compacted. After opening the cylindrical mold, the square mold was taken out together with the specimen. To the authors' best knowledge, this is the first attempt to ascertain the shear strength of the lowest zone of the rammed earth layer (see Figure 1). The sample installation was carried out in layers. For each layer, 3.5 kg of the mixture was prepared (before adding water to achieve the desired moisture content; the approximate height of the compacted layer was 10 cm). The direct shear test was carried out on specimens with dimensions of 100 \(\times\) 100 \(\times\) 20 mm (Figure 7), and the tests were carried out on specimens immediately after installation (labeled 1 day) and on specimens 7 and 28 days old that were cured under controlled conditions in a chamber with 55% relative humidity and at a temperature of 25 \({}^{\circ}\)C.  
Figure 6: Specim position inside the cylindrical mold (in mm). Figure 7: M5 specimen (**a**) before and (**b**) after the test conducted using direct shear device. The main objective was to ascertain the behavior of specimens that were cured for 28 days, which is the curing time recommended by the majority of the literature evaluated discussing rammed earth [26]. It was later discovered through field research that the moisture content in the walls of existing rammed earth houses can range from 6.5 to 8% at a height of approximately 0.50 m above the ground. The same research revealed that the moisture content in the walls of existing rammed earth houses is approximately 2% at a height of approximately 1.50 m above the ground. Consequently, it was decided to conduct additional tests on specimens cured for 1 and 7 days in an effort to identify a general pattern regarding the influence of relative humidity on the shear strength and cohesion. Although the Proctor test is generally used to determine the soil optimum moisture content [5; 37; 38; 39], the required moisture content of rammed earth materials can also be determined with a drop test [5; 37; 38]. In this research, the moisture contents determined by the drop test proved to be optimal for the compaction. The average moisture contents during installation were in the range of 13.0-20.3% (Table 4). However, as part of the study, a Proctor test (according to Ref. [40]) was also performed for samples M1-M4 in order to compare the results and determine the densities. For sample M1, the maximum dry density (MDD) of 1.69 g/cm\({}^{3}\) at the optimum moisture content (OMC) of 16.7% was determined. For sample M2, the MDD was 1.99 g/cm\({}^{3}\) at OMC 12.0%; for sample M3, the MDD was 1.98 g/cm\({}^{3}\) at OMC 11.3%, while for sample M4, the MMD was determined to be 2.01 g/cm\({}^{3}\) at OMC 10.5%. By comparison with the results shown in Table 4, it can be seen that the moisture content of the samples determined by the drop test is higher compared to the OMC determined by the Proctor test. However, [PERSON] [38] recommends the use of higher than optimal moisture contents and states that it was shown that a moisture content that was 10% higher than optimal gave better results for compressed soil blocks. Standard NZS 4298 [41] states that the moisture content during compaction (for rammed earth constructions) can be 6% higher or 4% lower than the established OMC. The moisture contents obtained by the drop test are in accordance with the mentioned values and recommendations. The mixtures were prepared 24 h prior to compaction in order to achieve a uniform moisture content of the sample.