## 5 Conclusions  
The physical properties, mechanical properties, and microstructure of diatomic soil in Zhejiang Province are studied through a series of geotechnical engineering tests in this paper. The mechanism of the deformation and mechanical properties of diatomic soil is analyzed from the macro and micro perspectives. The following conclusions are obtained:  
1. The diatomic soil has special properties different from general soil, including small particle size, low specific gravity value, high liquid-plastic limit, and high compressibility. The strength indexes \(c\) and \(\varphi\) of diatomic soil will decrease with an increase in water content because diatomic soil is rich in aluminosilicate and contains more kaolinite, mica, and other minerals in mineral composition, which will show strong water absorption and certain volume expansion. Furthermore, the water molecules affect the overlapping cell structure composed of silicon, aluminum, and oxygen. The strength of diatomic soil is greatly affected by water, which has a tremendously adverse effect on the stress and deformation of diatomic soil.
2. From the SEM analysis, it is found that the unique microstructure of diatomic soil increases the porosity of diatomic soil. When the diatomic soil is relatively dry and the pore is large, the inter layer structural force is mainly provided by the contact of particles, and the contact area is large--the soil structure is relatively stable. When the pores in the soil decrease and are filled by water, the soil particles adhere to each other under the suction. The XRD results show that there are many chemical elements in diatomic soil, including Si, K, Al, H, O, etc. These elements exist in the form of oxides in diatomic soil. This kind of diatomic soil has higher aluminum content. Aluminum is usually combined with other elements such as silicon and oxygen to form a variety of oxides and minerals.
3. In the triaxial test, when the dry density of diatomic soil increases from 1.30 g/cm\({}^{3}\) to 1.50 g/cm\({}^{3}\), the effective internal friction angle of diatomic soil increased from 5.6\({}^{\circ}\) to 14.5\({}^{\circ}\), and the effective cohesion increased from 30.9 kPa to 49.6 kPa. The stress-strain curve of diatomic soil changed from a weak softening type to a weak hardening type when the confining pressure was above 200 kPa. From the stress-strain curve, the linear equation curve of \(\varepsilon\) and \(\epsilon/(\sigma_{1}-\sigma_{3})\) can be fitted, and the fitting effect is good.  
Methodology, L.G.; validation, Y.L.; data curation, Y.L.; writing--original draft preparation, L.G., Y.L. and O.A.; writing--review and editing, L.G., Y.K. and M.G.; supervision, Y.K. and M.G.; project administration, L.G.; funding acquisition. All authors have read and agreed to the published version of the manuscript.  
Financial support comes from the National Natural Science Foundation of China (Grant No. 52027812), the Fundamental Research Funds for the Central Universities of Hohai University (No. B21020047, B210204020), Shaanxi Key RESEARCH and development Program (2021 SF-465) are gratefully appreciated.  
Not applicable.  
\begin{table}
\begin{tabular}{c c c c} \hline \(\rho_{d}\)/(g/cm\({}^{3}\)) & **Confining Pressure/kPa** & \(a\) **(10\({}^{-3}\))** & \(b\) **(10\({}^{-4}\))** \\ \hline  & 200 & 14.8 & 61 \\
1.40 & 300 & 21.0 & 51 \\  & 400 & 23.5 & 37 \\  & 200 & 3.1 & 34 \\
1.50 & 300 & 7 & 30 \\  & 400 & 12 & 20 \\ \hline \end{tabular} \(a=\) reciprocal of initial tangent modulus; \(b=\) reciprocal of limit deviation stress.  
\end{table}
Table 3: Fitting line parameters.