## 2 Uniaxial Compression Test on Earth Materials
### Experimental Results and Discussion  
The failure phenomena of the specimens are shown in Figures 6 and 7. It can be seen that the failure process and test phenomena of the cubic and cylindrical specimens are similar. At the early stage of the test, the specimen block did not change significantly with the increase in the load. When the load reached 55% of the peak load, fine cracks appeared in the corners of the cubic specimen and expanded rapidly. The cylindrical specimens showed small vertical cracks at the loaded end that extended to the lower part. When the load increased to its peak, there were several wide cracks through the surface of each specimen, and the skin swelled off. As the displacement continued to increase, the load continued to decrease. The cracks on the surface of the specimen fully developed, and the soil at the edge was flaked off, and the specimen was damaged due to the loss of its bearing capacity. The final failure pattern of all specimens is basically an hourglass-shaped.  
Figure 5: Specim loading diagram: (**a**) loading instrument; (**b**) cube specimen; and (**c**) cylindrical specimen.  
Figure 6: Test typical mode of failure in uniaxial compression for a cubic specimen: (**a**) middle stage of loading; (**b**) load to peak load; and (**c**) failure stage.  
Figure 7: Test typical mode of failure in an uniaxial compression for cylindrical specimen: (**a**) middle stage of loading; (**b**) load to peak load; and (**c**) failure stage.  
The mean compressive strength, peak compressive strain, and coefficient of variation of the specimens obtained under different working conditions, such as different curing ages, shapes, sizes, and loading rates, are shown in Table 5. The comparison of the compressive strength and the coefficient of variation of the strength of the specimens under different working conditions are shown in Figures 8 and 9, respectively. From Table 5 and Figures 8 and 9, the following rules can be drawn:  
* The compressive strength of the specimens increased with the increase in curing age. The compressive strengths of specimens Y\({}_{102}\)-14-0.2, Y\({}_{102}\)-21-0.2, and Y\({}_{102}\)-28-0.2 were 59% and 76% of 28 d at 14 d and 21 d, respectively. The reason is that the longer the age, the more sufficient the water loss hardening reaction inside the specimen. The internal soil particles have higher cohesion, stronger compactness, and higher compressive strength.
* With the increase in size, the strength of the specimen first increased and then decreased. A 100-mm-cube specimen had the highest strength, and the effect of the size factor on the compressive strength was more significant. A 70.7-mm-cube had 96% of the compressive strength of a 100-mm-cube. A 150-mm-cube had only 83% of the compressive strength of a 100-mm-cube.
* The specimen shape and loading rate have a slight effect on the compressive strength. The compressive strength of cylindrical specimens was 5.6% lower than that of cubic specimens. The compressive strengths of specimens with loading rates of 0.2 mm\(\cdot\)min\({}^{-1}\) and 3.0 mm\(\cdot\)min\({}^{-1}\) were 95.3% and 102.6% of the compressive strengths of specimens with 1 mm\(\cdot\)min\({}^{-1}\), respectively. The strength differences of the specimens were all within the range of 6%.
* It is recommended to use a 100 mm \(\times\) 100 mm \(\times\) 100 mm cube with a curing age of 28 d as the standard specimen. Then, 1.0 mm\(\cdot\)min\({}^{-1}\) was adopted as the recommended loading rate for uniaxial compression testing of earth materials. As can be seen from Figure 9, the strength coefficient of variation of the