# A New Soil Conditioner for Highly Permeable Sandy Gravel Stratum in EPBs
## 2 Materials and Methods  
### The Modified Slurry Modifier Components  
The traditional slurry is commonly the aqueous solution of sodium bentonite with 10-18 wt%. The preparation method added the weighted sodium bentonite powder to distilled water several times. It should be noted that the incorporation quality of sodium bentonite was less than 5 g to avoid an uneven blend and the solution was stirred at 1000 r/min.  
In this study, ammonium chloride, sodium silicate and high molecular polymers were mixed into the traditional slurry to modify and improve it, in which ammonium chloride was the viscosity modifier to adjust the reaction time. In order to distinguish the traditional slurry, the mixed solution of modifier and slurry was called modified slurry. In addition, high molecular polymers were helpful for enhancing the impermeability of the mixed system.  
In this study, the modified slurry preparation process mainly included two mixed solution systems, namely, the mixed solution of bentonite and sodium silicate as well as the mixed solution of ammonium chloride and high polymers. The sodium bentonite (Henan Zhongyuan Mining Company, Henan Province, China) chemical components and physical characteristics are shown in Tables 1 and 2. Ammonium chloride (Beijing Chemical Reagent Factory, Beijing, China) formed the viscosity modifier for modified materials. The ammonium chloride was analytically pure (>99%), the sodium silicate solution (Shandong Dongyue Group, Shandong Province, China) had a Baume Degree of 40, and the content was 34 wt%. There were 6 kinds of polymers. They are carbomer (97%, Sumitomo Chemical Co., Ltd., Tokyo, Japan), guar gum (99%, Guangzhou Feirui Chemical Co., Ltd. Company, Guangzhou, China), xanthan gum (99%, Fufeng Group, Jinan, China), carboxymethyl cellulose sodium (99%, Yixing Tongda Chemical Co., Ltd., Yixing, China), hydroxyethyl cellulose (99%, Shanghai Huiguang Fine Chemical Co., Ltd., Shanghai, China) and polyacrylamide (99%, Shandong Baomo Biochemical Co., Ltd., Dongying, China). Details of the components are shown in Table 3. Code B represents a solution of 13 wt% bentonite, other codes have similar meanings, and the solvent was water. In the process of polymer solution preparation, it should be noted that the weighed reagent was slowly added into the 50-60 \({}^{\circ}\)C distilled water and then the solution was stirred at 2000 r/min for more than 30 min until the solution was clear.  
Four different grades of sandy gravel soil samples were prepared in the laboratory, in which the coarse sand was selected from standard sand, the main mineral component was quartz, and the gravel was a natural breccia-like cobblestone whose main mineral composition was quartz and carbonate minerals. The gradation curve and dry density information are shown in Figure 1 and Table 4.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Ingredient** & **SiO2** & **Al2O3** & **Fe2O3** & **Na2O** & **MgO** & **K2O** & **TiO2** \\ \hline Content (\%) & 63.43 & 17.88 & 2.06 & 0.98 & 3.05 & 0.9 & 0.13 \\ \hline \end{tabular}
\end{table}
Table 1: Main chemical constituents of sodium bentonite.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Material Category/Use** & **Name** & **Concentration (wt\%)** & **Density (g/mL)** & **Code** \\ \hline Slurry & Sodium bentonite & 13 & 1.11 & B \\ Water shutoff agents & & Sodium silicate & 34 & 1.37 & S \\ reaction material & & Ammonium chloride & 20 & 1.04 & A \\ \hline \multirow{6}{*}{Polymers / Water shutoff agents} & Carbomer & 0.5 & 1.06 & Carbon \\  & Guar gum & 0.5 & 1.02 & Guar \\ \cline{1-1}  & Xanthan gum & 0.5 & 1.04 & Xanthan \\ \cline{1-1}  & Carboxymethyl & 0.5 & 1.04 & CMC \\ \cline{1-1}  & cellulose Sodium & 0.5 & 1.08 & HEC/H \\ \cline{1-1}  & Hydroxyethyl cellulose & 0.5 & 1.04 & PAM \\ \hline \end{tabular}
\end{table}
Table 3: Experimental materials.