# A New Soil Conditioner for Highly Permeable Sandy Gravel Stratum in EPBs
## 3 Results and Discussion
### Slump Test  
#### 3.2.1 Comparison of Traditional Slurry and B/A Modified Slurry  
A slump test, a common method for conditioned soil, was used in this study to evaluate the modification effectiveness of traditional and B/A modified slurry to sandy gravel samples with different diameters, including 0-2 mm, 2-4 mm, 6-9 mm and 10-20 mm. The results of the slump tests on the mixtures of various sandy gravel and slurry of 5%, 10% and 20% (volume ratio) are shown in Table 7 and Figure 5. The following results were observed:  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Match Ratio** & **Apparent Viscosity (mPa-s)** & **Status Description** \\ \hline \(13\) wt\% bentonite (B) & 18 & Good liquidity. \\ \(20\) wt\% NH4 Cl (A) & 0.5 & Very fluid, equivalent to water. \\ \(13\) wt\% bentonite: 20 wt\% NH4 Cl = 20:1 & 127 & Moderate consistency, inverted microflow. \\ \(13\) wt\% bentonite: 20 wt\% NH4 Cl = 10:1 & 146 & Consistency is high, inverted does not flow. \\ \(13\) wt\% bentonite: 20 wt\% NH4 Cl = 5:1 & 118 & Moderate consistency, inverted microflow. \\ \(13\) wt\% bentonite: 20 wt\% NH4 Cl = 10:3 & 79 & Less consistency, inverted flow. \\ \(13\) wt\% bentonite: 20 wt\% NH4 Cl = 5:2 & 56 & Small consistency, flowing after dumping. \\ \hline \hline \end{tabular}
\end{table}
Table 6: Apparent viscosity and cone penetration of different sample groups.  
Figure 4: (**a**) Effect of the B/A modified slurry dumping state under different ratios, and (**b**) Change of apparent viscosity with time.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample Group** & \multicolumn{2}{c}{**Injection Ratio**} & **5\%** & **10\%** & **20\%** \\ \cline{2-5}  & **Additive** & \multicolumn{2}{c}{**Average Slump (mm)**} \\ \hline \multirow{2}{*}{2–4 mm Gravel} & Traditional slurry & 158 & 170 & 178 \\  & B/A modified slurry & 155 & 136 & 0 \\ \multirow{2}{*}{6–9 mm Gravel} & Traditional slurry & 177 & 180 & 196 \\  & B/A Modified slurry & 172 & 162 & 0 \\ \multirow{2}{*}{10–20 mm Grave} & Traditional slurry & 162 & 168 & 174 \\  & B/A Modified slurry & 150 & 146 & 135 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Comparison of slump between slurry and B/A modified slurry.  
(1) As shown in Table 7, B/A modified slurry shows a positive effect on improving the plasticity of sandy gravel sample, while traditional slurry has the opposite effect. Furthermore, as the traditional slurry injection ratio increases, the slump of sand gravel sample gradually increases, because traditional slurry is fluid and thus its incorporation increases the flow ability of sand gravel. The addition of B/A modified slurry reduces the slump value because the voids of sand gravel are filled by B/A modified slurry and the cohesion between sand gravel particles is enhanced by B/A modified slurry. The slump value of the mixture of 20% B/A modified slurry and sand gravel samples with 2-4 mm and 6-9 mm diameter decreased to 0.  
(2) It can be seen from Figure 5 that slurry is prone to flow away from sand gravel pores and the amount of slurry loss increased with its injection ratio increasing, due to the large fluidity of traditional slurry and large voids of sand gravel sample, such as for the 6-9 mm (particle size) and 10-20 mm sand gravel samples mixed with 20% traditional slurry. In addition, the larger the size of sand gravel, the greater the loss degree of slurry occurs. This is because the increasing gravel diameter increases the porosity of the gravel.  
(3) As shown in Figure 5, the addition of B/A modified slurry significantly improved the cohesiveness of sand gravel particles. As the B/A modified slurry injection ratio increases the plasticity of the sand gravel samples gradually increases and its fluidity decreases.  
Figure 5: Comparison of slump between traditional slurry and B/A modified slurry at various injection ratios.