## 5 Discussion  
This study mainly focused on the absolute permeability and simulation of seepage process of Malan loess by CT scan images combined with the volume average method. The results of seepage experiment and seepage simulation were compared and the results of permeability coefficient calculated by simulation were compared and analyzed with the results measured by the ring knife method. In order to explore the pore morphology characteristics of the intact Malan loess, CT scanning technology was used in this study to scan the samples of intact Malan loess and to extract the pore morphology parameters of intact Malan loess [9]. It was found that the vertical pores of Malan loess were strongly developed and the center of gravity was evenly distributed in the vertical pores through the distribution of center of gravity coordinates. In the lateral direction, the coordinate distribution was normal. This also proved that the vertical permeability coefficient of intact Malan loess was larger than the lateral permeability coefficient [10; 11]. [PERSON] et al. measured the permeability coefficient of Malan loess in Jinya Township, Lanzhou, China using the ring knife method; the permeability coefficients ranged from 0.62 \(\times\) 10\({}^{-4}\) cm/s to 1.67 \(\times\) 10\({}^{-4}\) cm/s [8; 31; 47]. The permeability coefficient in the vertical direction calculated by using the CT scan image of intact Malan loess combined with the volume averaging method was 2.791 \(\times\) 10\({}^{-4}\) cm/s and the horizontal permeability coefficients were 3.093 \(\times\) 10\({}^{-5}\) cm/s and 7.23 \(\times\) 10\({}^{-5}\) cm/s, respectively, while the permeability coefficient of the soil samples around the samples measured with the ring knife sampling was 1.42 \(\times\) 10\({}^{-4}\) cm/s, which was slightly smaller than that of the permeability coefficients calculated by the simulation, because the ring knife may smash into the loess during the sampling process, thus compacting the loess and resulting in the permeability coefficient to become smaller. Calculating the permeability coefficient of Malan loess by sampling using the method mentioned in this paper can effectively avoid the measurement error due to the disturbance of the loess during the sampling process. In order to investigate the seepage process in the intact Malan loess, this study extracted the specific yield of the intact Malan loess using a homemade seepage device and observed the preferential conduction of water flow along the connected macropores on the surface of the intact Malan loess sample. This indicated that, given a certain head action, water flowed preferentially along the connected macropores in the intact Malan loess; then, the water filled the surrounding pores. This experimental method could also be used in the study of other experimental materials and could be used to study the seepage process of different porous media [3; 48; 49]. During the study of the porous media seepage process, the physical model was generally generalized and the model accuracy was not high. The CT scan section of the intact Malan loess sample was extracted by computerized tomography. The 3D pore structure of the intact Malan loess was reconstructed and the 3D pore morphological parameters of the intact Malan loess were extracted, which provided the base model for the water flow simulation and made the original black box model into a bright box model [9]. Comparing the seepage simulation model with the actual seepage experiment proved the reliability of the simulation model. The absolute permeability could be calculated by the seepage simulation and the absolute permeability tensor could be extracted, which provided a new idea for the calculation of absolute permeability. To perform the seepage simulation model with higher accuracy requires a higher accuracy CT scan of the sample to obtain a CT scan slice with higher resolution.