## 2 Experimental Program
### Experimental Procedure  
(1) XRD test  
Preparation of the XRD specimen and experiment procedure: Firstly, the experimental group specimen is drawn out and then dried in an oven. An appropriate amount of specimen is placed in mortar to grind into powder, then passed through a 0.075 mm geotechnical sieve. A multifunctional powder X-ray diffractometer, Panacol X'Pert3 Powder, The Netherlands, determines the specimen's phases.  
(2) MIP test  
Preparation of the MIP specimen and experimental procedure: Firstly, the experimental group specimen is drawn out and then dried in an oven. Then, the specimens with a length, width, and height of 1 mm \(\times\) 1 mm \(\times\) 1 mm are cut at the same position. The specimens are then dried by the liquid nitrogen freezing vacuum sublimation drying method to remove water. Finally, pores in the cement soil are measured by an Autopore 9510 mercury porosimeter produced by the Micrometrics company. The pore diameter distribution of the specimen is achieved.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Test Method** & \begin{tabular}{c} **Cement** \\ **Mixing Ratio** \\ **\(\beta\)/\%** \\ \end{tabular} & \begin{tabular}{c} **UFC** \\ **Proportion** \\ **\(\gamma\)/\%** \\ \end{tabular} & \begin{tabular}{c} **HA Content** \\ **\(\lambda\)/\%** \\ \end{tabular} & \begin{tabular}{c} **Moisture** \\ **Content** \(\omega\)/\% \\ \end{tabular} & \begin{tabular}{c} **Porosity Ratio** \\ **/e** \\ \end{tabular} & \begin{tabular}{c} **Soaking Time** \\ **Category** \\ \end{tabular} & \
\begin{tabular}{c} **Soaking Time** \\ **/d** \\ \end{tabular} \\ \hline \multirow{6}{*}{
\begin{tabular}{c} XRD, MIP, \\ SEM, PCAS, \\ UCS \\ \end{tabular} } & \multirow{6}{*}{20} & 0 & \multirow{6}{*}{15} & \multirow{6}{*}{24} & \multirow{6}{*}{1.2} & \multirow{6}{*}{1.2} & FA solution \\  & & & & & & (pH = 6.0) & \\ \cline{1-1} \cline{4-1} \cline{4-10}  & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Test design.  
(3) SEM test  
An SEM test is used to explore the micromorphological changes in UFC cement soil from a micro perspective. Preparation of the SEM specimen and experimental procedure: Firstly, the experimental group specimen is drawn out and then dried in an oven. The specimens with a length, width, and height of 30 mm \(\times\) 20 mm \(\times\) 15 mm are cut at the same position. The microstructure in the specimen is observed with a Czech TESCAN-VEGA3 fully automatic scanning electron microscope.  
(4) PCAS test  
PCAS preprocesses the SEM images and then extracts the corresponding microstructure parameter information through the microstructure processing program Pores and Cracks Analysis System (PCAS software, version number: V2.3) developed by the Department of Earth Science of Nanjing University. Finally, the pore distribution of cement soil specimens is statistically determined.  
(5) UCS test  
The UCS's macroscopic mechanical properties verify the microscopic analysis results. The UCS test is conducted with YSH-2 electric lime soil with no lateral limit compressive instrument produced by Nanjing Ningxi Soil Instrument Co., Ltd. (Nanjing, China) to determine the specimens' UCS with a 90 d immersion time. The arithmetic mean of the strength of the cement soil is the UCS. The test control instrument's axial compression rate was 1.0 mm/min.  
The test procedure and specimen preparation are shown in Figure 5[32; 33; 34].