# Experimental Study on the Mechanical Properties of Xinyang Red Clay Improved by Lime and Fly Ash
## 3 Test Results and Analysis
### Unconfined Compressive Strength Test  
The unconfined compressive strength of different improved red clay was tested. The variation of the unconfined compressive strength of improved red clay with different incorporation amounts of lime and fly ash is shown in Figure 5.  
As can be seen from Figure 5a, the unconfined compressive strength of red clay improved by lime only increases at first with the increase of lime content, and reaches a maximum value of 2.94 MPa when the lime content is 5%, which is 2.0 times higher than that of 0% lime content, and then decreases with the further increase of lime content. As can be seen from Figure 5b, the unconfined compressive strength of red clay improved by single fly ash increases at first, and then decreases with the further increase of fly ash content. When the fly ash content is 10%, the unconfined compressive strength reaches the minimum value of 0.84 MPa, and then increases with the increase of fly ash content. When the fly ash content is 20%, the unconfined compressive strength of the improved soil reaches the maximum value of 2.24 MPa. A comparative analysis of Figure 5a,b shows that, based on the unconfined compressive strength of the improved soil, it is not difficult to see that the red clay improved more by only mixing lime rather than fly ash. As can be seen from Figure 5c, the unconfined compressive strength of the modified soil increased at first  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Lime Content (\%)** & **Cohesion (kPa)** & **Friction** & **Fly Ash** & **Cohesion** & **Friction** & **Lime: Fly** & **Cohesion** & **Friction** \\
**Content (\%)** & **Content (\%)** & **Content (\%)** & **(kPa)** & **Angle (\({}^{\circ}\))** & **Soil** & **(kPa)** & **Angle (\({}^{\circ}\))** \\ \hline
2 & 18 & 14 & 5 & 26 & 11 & 0:0.1 & 30 & 12.5 \\
5 & 43 & 14 & 10 & 30 & 13 & 1:2.7 & 46 & 12.8 \\
8 & 38 & 15 & 15 & 36 & 12 & 1:36 & 32 & 10.2 \\
11 & 34 & 17 & 20 & 34 & 10 & 1:45 & 38 &with the soil ratio, and reached a maximum value of 2.98 MPa when the ratio is 1:2:7, and then decreased with the increase of the ratio.  
In the test, it was found that with the increase of fly ash incorporation, the improved soil gradually showed a certain brittleness. Particularly, the soil was improved by using lime-mixed fly ash. Figure 6 shows the failure of the unconfined compression test samples with different proportions. As can be seen from Figure 6, the included angle between the failure surface and the horizontal plane of the sample increases with the increase of the proportion of lime: fly ash: dry soil, and the sample has a clear fracture surface when the ratio is 1:2:7 and 1:3:6. When the ratio is 1:4:5, after the sample reaches a certain pressure in the process of compression, it is found that slag begins to drop at both ends of the sample and gradually transfers to the middle of the sample, resulting in the local block falling and slight cracking in the middle of the sample, and the fracture surface is almost perpendicular to the major principal stress surface.  
Figure 5: Curves of unconfined compressive strength with modified materials incorporated: (**a**) single lime, (**b**) single fly ash, and (**c**) mixed lime and fly ash.  
Figure 6: Failure modes of unconfined compressive test samples of modified soil with different proportions: (**a**) 1:2:7, (**b**) 1:3:6, and (**c**) 1:4:5.