## 3 Application Verification of Typical Karst Curtain Grouting Project
### Hydrogeological Conditions of Working Area
#### 3.2.2 Characteristics of the Water Permeability of Rock Strata in Working Area
The length of grouting section is 3-40 m. The grouting method is a downward-segmented pure-pressure method. The grouting material is modified clay-cement paste. The assessment and evaluation index of curtain grouting quality is the anti-seepage standard of grouting curtain, that is, when the water permeability of a single hole is not greater than 5 Lu in the water-pressure test of the inspection hole, it is considered that the grouting quality is better and meets the quality acceptance standard. 3.1 Prediction of the Unit Grouting Quantity in Curtain Grouting in the Area of Strong Karst Development by Using the Water Permeability of Rock Strata  
In the curtain grouting project, the northern curtain grouting area is an area of strong karst development. The purpose of this part is to verify the applicability of the proposed prediction method of the unit grouting quantity in the area of strong karst development. In the northern curtain grouting area, a typical section which can generally represent the characteristics of karst development in the grouting area is selected as the test section to carry out the field grouting test. Statistics are carried out on the data of the unit grouting quantity, and the water permeability of rock strata in the test section, and the correlation curve between the unit grouting quantity and the water permeability of rock strata is drawn by data fitting (as shown in Figure 6). As a result, the value of the comprehensive coefficient of karst curtain grouting (\(K\)) is 24.37, and the fitting equation between the unit grouting quantity and the water permeability of rock strata in the area of strong karst development is obtained:  
\[q_{w}=24.37\omega^{1.5}\qquad(R=0.91). \tag{17}\]  
According to Equation (17), the corresponding relationship between the water permeability of rock strata and the unit grouting quantity in the northern curtain grouting area can be obtained, as shown in Table 1.  
During the construction of the main project, the unit grouting quantity in the northern curtain grouting area is determined according to Table 1. After the construction of the karst curtain grouting project, the effect of the karst curtain grouting is tested and evaluated by means of grouting superposition effect analysis of each grouting hole, frequency curve analysis, variation curve analysis of the unit grouting quantity, and a water-pressure test in the inspection hole and drilling coring. The results show that an effective grouting curtain body is formed in the grouting area, according to the measured water permeability of rock strata before grouting in each grouting hole section at the construction site and selecting the corresponding unit grouting quantity from Table 1 for grouting construction. The effect of preventing seepage and blocking leakage is remarkable. The water permeability of rock strata measured by the water-pressure test in the inspection hole after grouting is less than 5 Lu, which \begin{table}
\begin{tabular}{c c} \hline \hline
**Water Permeability of Rock Strata (Lu)** & **Unit Grouting Quantity (kg/m)** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 1: The reference value of a certain water permeability of rock strata and corresponding unit grouting quantity in the northern curtain grouting area. Figure 6: The relationship curve between the unit grouting quantity and the water permeability of rock strata before grouting in each grouting hole section in the northern grouting test section. meets the anti-seepage standard of grouting curtain required in the current regulations and codes for hydraulic design and construction in China [27; 28]. Core samples of the drilling hole before and after grouting in the northern curtain grouting area are shown in Figure 7.  
Therefore, based on Equation (17), the unit grouting quantity in curtain grouting in the area of strong karst development predicted by the water permeability of rock strata can ensure the construction quality of the project.