## 5 Conclusions  
Based on the uniaxial compression test results of 48 earth specimens in eight groups, this study investigates the uniaxial compression test for four typical working conditions with different shapes, sizes, curing ages, and loading rates. The proposed uniaxial compression test method for earth materials is described. A modified uniaxial compressive constitutive equation for earth materials is established. Based on the verification of its applicability to soils in different regions of China, the calculation method of the relevant parameters of the constitutive equation for the earth is established. The conclusions are as follows:  
1. The uniaxial compressive strength of earth specimens increases significantly with the increase in curing age and shows a trend of first increasing and then decreasing with the increase in size. It is relatively little influenced by the shape and loading rate of the specimen. The uniaxial compressive test with 100-mm-cubic specimens at 28 d of curing age and 1 mm\(\cdot\)min\({}^{-1}\) loading rate can obtain stable test results with a small coefficient of variation of strength, which is recommended as the standard test method for the uniaxial compressive test of earth materials.
2. Based on [PERSON]'s constitutive equation, the modified constitutive equation of earth materials under uniaxial compression can better meet the compression failure mechanics and deformation characteristics of earth materials. It is a good fit for the uniaxial compressive test data of 100-mm-cubic standard specimens maintained for 28 d. It has good applicability to soils in different regions of China.
3. The calculation methods for the shape parameters of the rising and descending section curves and the peak compressive strain of the uniaxial compressive constitutive equation of the earth material under the condition of a 100-mm-cubic standard specimen at the age of 28 d of curing are established. The average values of the coefficients of determination R\({}^{2}\) for the shape parameters of the rising and descending sections of  
Figure 15: Fitting curve of compressive strength and peak compressive strain.  
the curve are 0.818 and 0.758, respectively, and the coefficient of determination R\({}^{2}\) for the peak compressive strain is 0.666, which is a good overall fit.
4. The modified constitutive equation and the calculation method for curve shape parameters and peak compressive strain are put forward. In the application, only the compressive strength of 100-mm-cubic standard specimens at 28 d curing age is measured, and the specific values of the relevant parameters of the constitutive equation can be calculated and determined. This is a good reference value to promote the development of computational analysis methods for earth structures and to facilitate the engineering design applications of earth structures.  
Conceptualization, J.Y. and K.Y.; Data curation, F.Z.; Supervision, K.Y.; Validation, F.Z.; Visualization, L.G.; Software, L.G.; Writing--original draft, J.Y.; Writing--review and editing, K.Y.; Funding acquisition, K.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China, grant number 2018 YFD1100402-03, and the Science and Technology Leading Talent Program of Young and Middle-Aged Corps, grant number: 2020 CB033.  
Not applicable.  
The authors declare no conflict of interest.