## 4 Discussion  
Comparison of the pore parameters reveals significant differences in the pore structure of the intact and remolded specimens formed through different processes. Overall, intact loess generally exhibits a more uniform structure with better pore connectivity compared to remolded loess. The Q\({}_{3}\) loess shows higher connectivity and greater heterogeneity than Q\({}_{2}\). Additionally, the heterogeneity of the F1 remolded loess is more pronounced with the poorest connectivity. These characteristics are visually illustrated in Figure 14.  
For the Q\({}_{3}\) loess, large pores exhibit a heterogeneous distribution across all three directions (XY, XZ, and YZ projections) (Figure 14a), which enhances pore connectivity. For the F1 specimen, the heterogeneity is particularly pronounced, with grain-concentrated regions observable in the XY, YZ, and XZ directions. In contrast, the pores in the Q\({}_{2}\) loess are evenly distributed, contributing to a more uniform microstructure. The C1 specimen, due to its higher dry density, is more compacted.  
It is observed that there exists a \"space pore\" or \"overhead pore\" both in the Q\({}_{3}\) and Q\({}_{2}\) loess, which has a diameter larger than the surrounding particles [36,52]. These voids are created by the loose accumulation of particles. It can sustain stability under natural dry conditions. However, the structure may lose stability under pressure and water infiltration conditions, which weakens the bonding or connection strength between particles, causing particles around the pores to collapse into the voids, and leading to collapse deformation [36,39,52]. The prevalence of the overhead pore in the Q\({}_{3}\) loess implies an under-compacted state with low strength and stiffness. In comparison, the Q\({}_{2}\) has a more dense and uniform structure with fewer space pores. The Q\({}_{2}\) loess experiences long-term evolution under the influence of climate factors (i.e., precipitation, evaporation), biological activity, etc. The infiltrating water can dissolve soluble salts, causing transportation and reprecipitation of calcium carbonates and reinforcing existing pores through cementation [53,54]. The prolonged period of water seepage promotes the formation of connected pores [55], contributing to a more uniform and connective structure.  
Figure 13: Absolute permeability of the tested specimens (**a**) Diagram of the numerical permeability experiment; (**b**) Permeability results.  
On the other hand, the remolded loess is more compacted with smaller pores. The F1 specimen from the GMRL site has more isolated pores, more heterogeneous structure, and poorer connectivity than the C1 specimen from the MECC project. For the remolded loess in the GMRL project, the soil was not uniformly and systematically compacted before utilization (e.g., planting [9,13]). The soil underwent complex wet-dry cycles and was influenced by plant root systems, leading to numerous particle aggregates, isolated pores, and poor pore connectivity. In contrast, at the MECC site, the remolded loess underwent standardized compaction treatments, and external force was applied to achieve the desired state.