## 3 Results and Discussion  
The direct shear tests included samples of different particle size distributions, line proportions, cereal straws and hemp fibers in order to determine the influence of individual parameters. A comparison of peak shear stress values (\(\tau\)) for samples M1 to M4 that had a different soil composition is shown in Figure 8, where an increase in shear stresses (an increase in the sample strength) can be seen with the age of the sample. This can be attributed to the fact that the samples dried over time, i.e., lost moisture content. It can be seen that the lowest peak shear stress values were recorded for sample M1, which has the largest proportion of fine particles. Samples with a smaller content of cohesive soil, M2 and M3, proved to be better, that is, they had the highest strength. The exception is sample M3 at a vertical stress of 25 kPa, where a lower shear stress value was recorded after 28 days, possibly due to a certain sample disturbance. At lower vertical stress levels, for 1-day samples M1-M4, the approximate values of peak shear stress were recorded. However, since the observed samples or mixtures would be inside the formwork after installation (in rammed earth walls), the strength values of the aged samples are of interest. In the RE-forMS project [43], within the framework of which this research was also carried out, research was additionally planned and is being carried out with a broader range of particle size distributions of rammed earth mixtures (e.g., a higher proportion of gravel) in order to be able to outline the recommended grading curves for the area of eastern Croatia. For the purpose of improving strength, a certain proportion of lime was added to samples M5 and M6. Figure 9 shows a comparison of the peak shear stresses of samples that have the same particle size distributions, but where the lime content is varied. That is, sample M4 does not contain lime, sample M5 has 4% of lime (by mass), while sample M6 has 8% of lime (by mass). In these samples, too, approximately the same strength is visible as in the 1-day samples, that is, the stabilized samples had slightly higher peak shear stress values. Figure 8: Comparison of peak shear stress values of samples M1–M4 (influence of soil composition) for samples aged 1 day, 7 days and 28 days: (**a**) \(\sigma_{\text{n}}\) = 25 kPa; (**b**) \(\sigma_{\text{n}}\) = 50 kPa; (**c**) \(\sigma_{\text{n}}\) = 100 kPa. Although in unstabilized samples (samples M1-M4), an increase in peak shear stresses was recorded with the sample age, in stabilized samples, a certain increase was recorded in the 7-day-old samples, while in the 28-day-old samples, there was mostly a decrease in the value of the peak shear stresses compared to the 7-day-old samples. Stabilized samples aged 7 days recorded higher strengths than unstabilized samples. As part of the RE-forMS project [43], it is planned to further investigate the influence of lime and the aforementioned phenomena. The samples with a lower lime content had a more balanced behavior, i.e., a weaker increase or smaller decrease in strength, compared to the samples with a higher lime content. If the results of samples aged 7 days are excluded from the analysis, the samples with 4% of lime appear to be better. It can be concluded that a lower lime content is more suitable for rammed earth mixtures. This is in line with the observations in Ref. [33], where it was noted that the addition of more than 4% lime to the mixture did not further contribute to an increase in UCS and stiffness. The optimum lime content for the observed  
Figure 9: Comparison of peak shear stress values of samples M4–M6 (influence of lime) for samples aged 1 day, 7 days and 28 days: (**a**) \(\sigma_{\rm n}=25\) kPa; (**b**) \(\sigma_{\rm n}=50\) kPa; (**c**) \(\sigma_{\rm n}=100\) kPa. mixture in the current research needs to be further investigated. It is also recommended to carry out tests to determine the optimum content prior to the construction of lime-stabilized rammed earth houses.