## 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 water-pressure test before grouting is carried out in the grouting hole used to expose the karst on the curtain line. The statistical results of the subsection and sublevel of the water-pressure test are shown in Figure 5. Figure 5 shows that, on the whole, the water permeability of rock strata is more than 100 Lu, which is mainly distributed above the elevation of \(-80\) m, accounting for 100% of the same permeability range, and the water permeability of rock strata accounts for 76.19% of the same permeability range in 10-100 Lu segment. The water permeability of rock strata in 5-10 Lu segment accounts for 67.11% of the same permeability range. This shows that the segment above the elevation is strongly permeable. In the elevation of \(-80\) to \(-120\) m, the water permeability of rock strata accounts  
Figure 3: The plane position diagram of the axis of the curtain. for 16.67% of the same permeability range in 10-100 Lu segment, and the water permeability of rock strata accounts for 18.42% of the same permeability range in 5-10 Lu segment. This shows that the segment is a medium permeability segment. In the elevation of \(-\)120 to \(-\)150 m, the water permeability of rock strata accounts for 7.14% of the same permeability range in 10-100 Lu segment, and the water permeability of rock strata accounts for 14.47% of the same permeability range in 5-10 Lu segment. This shows that the segment is weakly permeable. It can be seen that the water permeability of rock strata in the curtain protection area decreases with the increase of the depth of strata, mainly because the degree of development of karst decreases with the increase in the depth of strata, and the low density of karst cracks in the deep position of strata leads to the decrease of the water permeability of rock strata. Figure 4: The statistical results of karst revealed by drilling. Figure 5: The statistical results of the subsegment and sub-elevation of the water-pressure test in Shang-Lun formation on curtain axis. Engineering Application of Prediction Method of the Unit Grouting Quantity in Karst Curtain Grouting Based on the Water Permeability of Rock Strata  
According to the characteristics of karst development, the curtain grouting project divides the construction area into two curtain grouting sections: the south and the north. Among them, the northern curtain grouting area is an area of strong karstification, while the southern curtain grouting area is an area of weak karstification. The curtain grouting project mainly includes two parts: the curtain grouting test and the curtain grouting construction. The purpose of the field grouting test is to provide sample data for determining the comprehensive coefficient of karst curtain grouting (\(K\)) in the theoretical relationship equation between the unit grouting quantity and the water permeability of rock strata in karst curtain grouting (Equation (16)). At the same time, it also provides relevant technical parameters for formal grouting design and construction. The grouting technology and parameters adopted in the curtain grouting test are determined according to the actual conditions of the construction area and the practice of similar karst curtain grouting projects. In the grouting test section, double-row linear holes are used, and the row spacing is 3 m. First, a row of holes on the side of the mining area (west side) will be constructed, and then a row of holes on the side of the Qianjiang River (east side) will be constructed. Each row of holes is constructed in two sequences. First, the first sequence hole is constructed, and then the second sequence hole is constructed. In the grouting test, the top of the curtain body is this position, which is 2 m above the boundary between the rock and soil, and the elevation of the curtain bottom is \(-150\) m. The opening diameter of grouting hole is not less than 110 mm, and the end diameter of grouting hole is not less than 75 mm.