## 3 Results and Discussion
Figure 10 shows the test results of sample M4 (sample without additives) and samples M7-M11, which have the same particle size distributions but also additives of cereal straw or hemp fibers. The measurements show an increase in strength with the age of the sample, i.e., with a decrease in moisture content. The influence of straw and fibers on peak shear stress values for 1-day samples was not recorded or was negligible. A similar case applies to samples aged 7 days. The greatest influence on the sample shear strength is evident in the samples aged 28 days, where most had higher peak shear stresses compared to sample M4. The exception is sample M11 (sample with hemp fibers) at a vertical stress of 100 kPa, where a certain degree of sample disturbance occurred during the sample installation in the shearbox. Generally, the sample with the rye straw (M10) proved to be the best. A good contribution to strength was also recorded for the samples with barley (M7) and oat straw (M8). Figure 10: Comparison of peak shear stress values of samples M4 and M7-M11 (influence of natural fibers) for samples aged 1 day, 7 days and 28 days: (**a**) \(\sigma_{n}\) = 25 kPa; (**b**) \(\sigma_{n}\) = 50 kPa; (**c**) \(\sigma_{n}\) = 100 kPa. If the measurement for specimen M11 at a vertical stress level of 100 kPa for a sample aged 28 days is disregarded, the contribution of hemp fibers to sample shear strength could match that of rye and oat straw. This comparison proves the suitability of using the straw of the observed cereals and hemp fibers as micro-reinforcement in rammed earth mixtures. The calculated values of the strength parameters for samples M1-M9 are shown in Figures 11-13. There was no uniform trend of change in the cohesion values of the observed samples with sample ageing. However, all samples aged 28 days had higher values of cohesion compared to those of 1-day samples. The 1-day sample M1, which had a high content of fine particles, had the highest moisture content during installation and after testing. Since the shear rate was 1 mm/min, it is possible that the sample was closer to the undrained state, which is indicated by the approximate peak shear strength values but also by the very low value of the internal friction angle. In the case of the remaining samples, the moisture content was lower, as was the content of fine particles, and therefore, the reported state of the material was not so pronounced. It should be kept in mind that due to the high shear rate, the achieved values of cohesion and of the internal friction angle do not necessarily represent the values of cohesion and the internal friction angle that correspond to the results of a standard test at lower shear rates. Figure 11: Cohesion and internal friction angle values change with specimen age, samples M1–M4 (influence of soil composition): (**a**) cohesion; (**b**) internal friction angle. Figure 12: Cohesion and internal friction angle values change with specimen age, samples M4–M6 (influence of lime): (**a**) cohesion; (**b**) internal friction angle. Samples stabilized with lime recorded a decrease in cohesion in the samples aged 28 days compared to the samples aged 7 days. Water loss may be the cause of this. As part of the RE-forMS project [43], this phenomenon will be additionally studied. The overall cohesion values were reported to range from 14.4 kPa to 35.7 kPa, with an average value of 19.6 kPa (average calculated without the cohesion value of sample M1) for 1-day samples. For samples aged 28 days, the cohesion values ranged from 23.8 kPa to 62.0 kPa, with an average value of 46.7 kPa. The average increase in the cohesion value (samples aged 28 days compared to the 1-day samples, except for sample M1) was 138.5%. There was no uniform trend of change in the value of the internal friction angle with sample age. In most cases, the values of the internal friction angle were higher for the samples aged 28 days compared to the 1-day samples. The exception was sample M6, where a lower value of the internal friction angle was recorded.