## 4 Discussion  
### Parameter Analysis  
In the theoretical relationship equation between the unit grouting quantity and the water permeability of rock strata in karst curtain grouting, the comprehensive coefficient of karst curtain grouting (\(K\)) is introduced, which simplifies the form of the relationship equation. The key to the success of the grouting prediction model is that it must reflect the main attributes and characteristics of the grouting project. The comprehensive coefficient of karst curtain grouting (\(K\)) is a complex coefficient, and the physical quantities it contains basically reflect the three controlling factors of slurry diffusion, namely, the characteristics of slurry fluid, the characteristics of grouted rock strata, and the technical factors of grouting, which theoretically ensure the rationality of the grouting prediction model proposed in this paper. The comprehensive coefficient of karst curtain grouting (\(K\)) describes the quantitative relationship between the unit grouting quantity and the water permeability of rock strata. In the typical case of the karst curtain grouting project studied in this paper, the unit grouting quantity in the northern curtain grouting area is obviously larger than that in the southern curtain grouting area. The main reason for this difference is that the degree of karst development in the two curtain grouting areas is different. The northern curtain grouting area is an area of strong karst development, so the three controlling factors of slurry diffusion are more complex, and the comprehensive coefficient of karst curtain grouting (\(K\)) is larger. The southern curtain grouting area is an area of weak karst development, so the three controlling factors of slurry diffusion are relatively simple, and the comprehensive coefficient of karst curtain grouting (\(K\)) is smaller. The comprehensive coefficient of karst curtain grouting (\(K\)) reflects the sensitivity of the unit grouting quantity to the water permeability of rock strata in karst curtain grouting. The unit grouting quantity in karst curtain grouting is affected by many factors, most of which have the uncertain characteristics of randomness and fuzziness, and many of them often influence each other. In the theoretical equation, the comprehensive coefficient of karst curtain grouting (\(K\)) is used to comprehensively reflect the influence of these factors on the unit grouting quantity, but it is difficult to solve its value theoretically. Therefore, how to simplify the influencing factors of the model in order to realize the theoretical solution of the coefficient is worthy of further study. In this paper, the field test and data fitting are used to determine the value of the comprehensive coefficient of karst curtain grouting (\(K\)), and the engineering application proves the feasibility of this parameter-determination method. In the theoretical relationship equation between the unit grouting quantity and the water permeability of rock strata in karst curtain grouting, the power of the water permeability of rock strata (\(\omega\)) is 1.5, which is a constant. This constant is inferred on the basis of the existing theoretical formula. Figure 9: Core samples before and after grouting in southern curtain grouting area. (**a**) Core samples before grouting; (**b**) core samples after grouting. In engineering application, the fitting equations (Equations (17) and (18)) suitable for different karst development conditions are obtained by field tests and data fitting. In the process of data fitting, both the parameter \(K\) and the power are free quantities. When the fitting converges, it is obtained that \(K\) is 24.37 and the power is 1.5 in the area of strong karst development, and \(K\) is 16.51 and the power is 1.5 in the area of weak karst development.