## 3 Influencing Factors and Data Preprocessing  
### Selection of Influencing Factors  
The Ordos Basin is currently China's main coal-producing and energy strategy implementation region [11; 12; 13]. As the scale and intensity of the Jurassic coal seam mining in the Ordos Basin increase, it has gradually entered deep mining. Due to the complexity of geological structures and aquifers, accurate prediction of the height of water flowing fractured zone has become an important content of water-preserving mining.  
Based on the engineering geology and technical mining conditions of the Jurassic coal seams in the middle and deep part of the Inner Mongolia-Shaanxi border area, five influencing factors, i.e., mining method, the ratio of the thickness of hard rock layers and soft rock layers in the bedrock, buried depth, mining height, and working face length, were used as the model's input vectors. The measured height of water flowing fractured zone was used as the model's output vectors. The reasons for selecting these factors as predictive features are as follows:  
1. Mining method (I\({}_{\rm m}\));  
The mining method has specific requirements for the mining height. Different mining methods selected under different geological conditions have different effects on the damage degree and damage range of the roof.  
2. The ratio of the thickness of hard rock layers and soft rock layers in the bedrock (I\({}_{\rm r}\));  
The bedrock in this area is thick, the soft and hard rock layers are distributed alternately, and there are many key strati in bedrock that control rock strata movement and mining-induced fracture development, which brings great difficulty to the accurate prediction of the height of WFFZ. Rock strata with a Platts coefficient (the value is 1/10 of the uniaxial compressive strength limit of rock or soil) less than 3 were defined as soft rock, and rock strata greater than or equal to 3 were defined as hard rock. In the process of working face mining, soft rock is apt to produce plastic strain, closes the overburden fractures, in turn, makes the height of WFFZ decrease. While hard rock strata are prone to cause deformation and failure in a larger range after fracture, resulting in a highly nonlinear mutation of the WFFZ. Therefore, the ratio of the thickness of the hard rock to the soft rock within the range of bedrock is chosen as an index reflecting the structure of the overlying rock.  
3. Buried depth (I\({}_{\rm d}\));  
According to the theory of rock mechanics, the deeper the coal seam is buried, the greater the stress on the overlying rock, and the more drastic the degree of deformation and destruction of the corresponding overlying strata after mining.  
4. Mining height (I\({}_{\rm h}\));  
In the empirical formula for calculating the height of WFFZ, the mining height is an essential parameter. The larger the mining height, the greater the scope of plastic failure zone of rooves.  
5. Working face length (I\({}_{\rm l}\)).  
The length of the working face is an important factor affecting the development of the WFFZ. Before critical mining is achieved, the height of the water-flowing fractured zone increases with the increase of the working face length [14].