# Triaxial Test of Coarse-Grained Soils Reinforced with One Layer of Geogrid
## 3 Test Results
### Dependence on Soil Properties  
The type of soil was observed to exert a noteworthy influence on the vertical strain at which the maximum deviatoric stress was achieved. Figure 7 illustrates the influence of vertical strain based on soil type and the geogrid reinforcement. In gravel samples without geogrids, the vertical strain ranged from 2.64 to 3.43, while in the presence of geogrid reinforcement, it extended from 3.58 to 4.01. In contrast, sand samples displayed lower values of vertical strain, within the range of 2.37 to 2.87. Moreover, the influence of the geogrid on sand samples was less pronounced, with the vertical strain ranging from 2.53 to 2.84. This signifies the geogrid's distinct influence in various soil types, with gravel samples exhibiting a more substantial response to reinforcement in terms of vertical strain when compared to sand samples. Figure 7: Vertical strain at maximum deviatoric stress. The influence of the geogrid on the angle of internal friction and cohesion values is presented in Table 6. The geogrid had a positive influence on the angle of internal friction only for soil No. 2, increasing it by 0.41\({}^{\circ}\). For the other samples, the angle of internal friction decreased from 0.23 to 0.73\({}^{\circ}\). The geogrid increased cohesion for all investigated soil samples. The apparent cohesion of the gravel soils increased from 7.03 to 10.10 kPa, and the apparent cohesion of the sandy soils increased from 3.61 to 9.94 kPa. The type of soil has an influence on deviatoric stress. Deviatoric stress was higher for gravelly soil than for sandy soil at all cell pressures, as shown in Figure 8. A strong dependence of deviatoric strength on the initial specimen density was observed. When the sand samples were not reinforced with geogrids, the deviatoric stress increased slightly with increasing density. For sandy soils reinforced with geogrids, deviatoric strength increased more with increasing density, whereas for gravel soils, this phenomenon was not as pronounced. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Without Geogrid**} & \multicolumn{2}{c}{**With Geogrid**} & \multicolumn{2}{c}{**Difference**} \\ \cline{2-7}  & \(\boldsymbol{\varphi_{\text{mean}}}^{\circ}\) & \(\boldsymbol{\epsilon_{\text{mean}}}\), kPa & \(\boldsymbol{\varphi_{\text{mean}}}^{\circ}\) & \(\boldsymbol{\epsilon_{\text{mean}}}\), kPa & \(\boldsymbol{\varphi_{\text{mean}}}^{\circ}\) & \(\boldsymbol{\epsilon_{\text{mean}}}\), kPa \\ \hline
1 & 48.38 & 0.00 & 48.15 & 7.03 & \(-\)0.23 & 7.03 \\
2 & 48.46 & 6.29 & 48.87 & 16.39 & 0.41 & 10.10 \\
3 & 46.35 & 0.85 & 45.76 & 9.31 & \(-\)0.59 & 8.47 \\
4 & 44.24 & 0.00 & 43.98 & 3.61 & \(-\)0.26 & 3.61 \\
5 & 45.44 & 0.00 & 44.71 & 9.94 & \(-\)0.73 & 9.94 \\
6 & 43.10 & 1.81 & 42.38 & 10.65 & \(-\)0.30 & 8.84 \\ \hline \hline \end{tabular}  
* Sample numbering coincides with the numbering given in Table 1.  
\end{table} 
Table 6: Summary of the results of the triaxial compression test for the angle of internal friction and cohesion. Figure 8: \(Cont\). The dependence of deviatoric strength on the coefficient of uniformity was also observed, as depicted in Figure 8. It is important to note that sandy and gravelly soils must be evaluated separately. The slope angles of the curves exhibited little variation with soil type or cell pressure, but the x-axis crossing points had higher values for gravelly soil compared to sandy soil. Conclusively, the soil's mechanical properties are predominantly determined by density or the coefficient of uniformity. This assertion is supported by the observation that gravelly soil consistently exhibits higher deviatoric strength compared to sand. Examining the relationship between \(\mathrm{C_{u}}\) and density in Figure 9 reveals a consistent trend: as \(\mathrm{C_{u}}\) increases, density also increases. This correlation holds true for both sandy and gravelly soils, indicating that the soil type does not significantly influence this particular association.