# A New Soil Conditioner for Highly Permeable Sandy Gravel Stratum in EPBs
## 2 Materials and Methods
### Slurries Conditioner Preparation  
Modified slurry is a mixed material prepared by adding ammonium chloride, sodium silicate and high molecular polymer into traditional slurry. In the preparation process of the modified slurry, the traditional slurry and each modifier solution were separately configured. Before the relevant tests, the solutions were mixed according to the experimental design ratio, and then stirred evenly with a glass rod.  
In engineering applications, all fluid materials (such as slurry, foam, polymers solution, etc.) must be pumped into the excavation chamber, which consequently requires the materials to have good fluidity. On the one hand, the high apparent viscosity and non-flowing state of the modified slurry are the key to improving the plasticity and water blocking of sand and gravel soil. On the other hand, the fluidity of the slurry is a prerequisite for actual engineering use. Based on that, the traditional slurry and modifier solution involved in this article need fluid composition with good fluidity to ensure that the material can be easily pumped into the excavation cabin to mix and react to form a modified slurry.  
In this study, the main objective was to obtain the traditional slurry with moderate apparent viscosity, good time stability and fluidity. The apparent viscosity of traditional slurry samples with four bentonite concentrations (i.e., 10 wt%, 13 wt%, 15 wt% and 18 wt%) over time (0-50 h) are measured. The dumping method was used to compare with and analyze the slurry flow corresponding to different apparent viscosity values, and then the fluidity of each experimental group was evaluated. Afterwards, the optimal bentonite concentration was obtained. In order to study the apparent viscosity and fluidity of the mixed system after adding ammonium chloride solution to the traditional slurry, the experimental goals were to obtain the modified slurry with high apparent viscosity and low fluidity. In this study, five ratios of bentonite slurry and ammonium chloride solution were selected (B:A = 20:1, 10:1, 5: 1, 10: 3 and 5:2).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sand Gravel** & \multicolumn{2}{c}{**Coarse Sand**} & \multicolumn{3}{c}{**Gravel**} \\ \cline{2-6}
**Size** & **0–2 mm** & **2–4 mm** & **4–6 mm** & **6–9 mm** & **10–20 mm** \\ \hline Dry Density & 1.77 & 1.77 & 1.78 & 1.71 & 1.66 \\ (g/mL) & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Sand gravel material physical characteristics.  
Figure 1: Experimental sandy gravel particle grading curve.  
To study the effect of ammonium chloride on the water absorption time of bentonite slurry, six modifiers were prepared with different ammonium chloride concentrations, one modifier was used (i.e., Ammonium Chloride) but in six different ratios, one containing no ammonium chloride as a control. At this stage, no further additive was included in the mixture. The details are shown in Table 5. The preparation process was as follows: a certain amount of water was added to the beaker, then bentonite with 13 wt% was added slowly to the beaker and the solution was stirred for another 30 min until there were no lumps on the surface and no sediment at the bottom of the solution (note that, through the process, the stir rate of the magnetic stirrer was 1500 r/m)). According to the solution dissolution efficiency and the experiment results, the optimum dissolved concentration of ammonium chloride was 20 wt%. In this study, the slurry solution was mainly composed of bentonite (B) and ammonium chloride (A), which is called B/A modified slurry. B/A refers to the mixture mainly formed by B and A.  
In addition, to study the influence of sodium silicate concentration and polymers types on the impermeability improvement degree of soil, the conditioners containing different concentrations of sodium silicate and different types of polymers were prepared.