# Strength Characteristics and Slope Stability Analysis of Expansive Soil with Filled Fissures
## 4 Analysis of Strength Characteristics of Expansive Soil with Filled Fissures  
### Analysis of Stress-Strain Curve and Deformation Characteristics  
Figure 5 shows the typical failure modes of triaxial sample without a filled fissure, and triaxial samples with a filled fissure with an inclination angle of 15\({}^{\circ}\), 30\({}^{\circ}\) and 45\({}^{\circ}\). The stress-strain curve of each sample is shown in Figure 6.  
The failure mode of the soil without a filled fissure was a typical triaxial test failure mode, and shear failure occurred at an angle of approximately 45\({}^{\circ}\) + \(\varphi\)/2 to the horizontal direction of the sample. The deformation of the expansive soil was strain hardening. The shear stress increased rapidly after \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Soil Type** & **Moisture Content (\%)** & **Density (g/cm\({}^{3}\))** & \multicolumn{2}{c}{**Particle Composition (\%)**} & **Liquid** & **Plastic** & **Free Expansion** \\ \cline{3-8}  & & & **Silt** & **Clay** & **Limit (\%)** & **Limit (\%)** & **Rate (\%)** \\ \hline Filled & 31.56 & 1.93 & 7 & 93 & 90.11 & 29.46 & 110 \\ fissure & 22.12 & 1.92 & 19 & 81 & 57.32 & 23.05 & 70 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Basic physical properties of the soils in the sample. Figure 5: Failure modes of the triaxial samples. (**a**) Without a filled fissure; (**b**) filled fissure with an inclination angle of 15\({}^{\circ}\); (**c**) filled fissure with an inclination angle of 30\({}^{\circ}\); (**d**) filled fissure with an inclination angle of 45\({}^{\circ}\). the test started. When the strain reached about 5%, the growth rate gradually slowed down, the sample began to fail, and the shear stress quickly reached the peak value. After that, the shear stress remained basically stable, and the deformation of the soil appeared as plastic sliding along the shear surface. This strain hardening characteristic became more and more significant as the confining pressure increased. The failure of a sample with a filled fissure of 15\({}^{\circ}\) inclination angle was similar to that of a sample without a filled fissure, but bulging deformation occurred near the filled fissure. The reason for this was that the strength of the fissure filling clay was lower than that of the soil matrix. When the sample was subjected to axial partial stress, a large deformation first occurred in the weak part. When this deformation developed to a certain extent, the upper and lower expansive soil matrix gradually approached, and the filling clay lost the space for lateral deformation. The deformation characteristics of the sample gradually approached the state of sample without fissure, and the failure mode of the conventional triaxial test appeared. The shear plane did not develop along the 15\({}^{\circ}\) slow-inclined fissure, but remained at the theoretical 45\({}^{\circ}\) + \(\varphi\)/2, and then the failure characteristics of shear plane cutting and filling fissures appear. This shows the failure characteristics of shear plane cutting the filled fissure. The stress-strain curve showed a certain degree of downward movement, indicating that the filled fissure had an attenuating effect on the strength of the soil. Under low confining pressure, the downward movement amplitude was small, which was basically the same as that of no filled fissure. With the increase in confining pressure, the downward movement was getting larger and larger. At the load level of 250 kPa, the ultimate strength of the sample without a filled fissure was close to 300 kPa, while the strength of the sample with 15\({}^{\circ}\) inclination was close to 200 kPa. The deformation was still strain hardening. After the sample with a 30\({}^{\circ}\) inclination filled fissure was destroyed, its shear plane was fully developed in the 7 mm-thick filled fissure.