## 4 Infiltration Mode and Stabilization Mechanism  
The results of the tests performed in this work showed that the ADNB polymer was an effective soil stabilization material which infiltrated the soil and formed a protective shell of a certain thickness on the soil surface. The process of infiltration and the stabilization mechanism of the polymer emulsion are shown in Figure 9. The untreated aggregates were composed of numerous particles and contained pores of varying sizes benefiting the circulation of air and water (Figure 9a). In contrast to the penetration behavior of water in soil, viscous polymer emulsions enclosed soil particles through bonding during infiltration. The thickness of the polymer emulsion on the outer aggregate particles was more important than that of emulsion on the inner particles (Figure 9b). Figure 8: Aggregates treated with 0.5% ADNB (left) and 5.0% ADNB (right). Figure 7: \(K\) values of the different aggregates treated with ADNB. The polymer emulsion first adhered to the external soil particles, which reduced the number of pores in the surface soil layer. On the other hand, water, which has a low viscosity, first reached the inner aggregates and filled the pores, which prevented the continuous infiltration of the polymer emulsion. Therefore, the quantity of infiltrated polymer in the interior of the aggregate was greatly decreased. As a result, an increasing amount of polymer emulsion gathered on the surface of the aggregate (Figure 9c). Inside the aggregate, the water would prevent the polymer from adhering to the inner soil particles. When the aggregate had been completely infiltrated by water, the polymer emulsion could not be driven by water to continue the infiltration due to the lack of water flow potential. Without ADNB, the internal soil particles could not be stabilized (Figure 9b). When the water in the solution evaporated, polymer coated the soil particles and formed a soil-polymer matrix that acted as a stabilized shell of a certain thickness (Figure 9d). SEM images of the aggregates showed two ways for ADNB to stabilize particles: a membrane structure and chain bonding. The surface of the aggregate treated with 2% ADNB is shown in Figure 10a, which indicated that a smooth surface morphology had formed resulting from polymer molecules filling the pores and the bonding between particles. Figure 10b shows the surface of the aggregate treated with 5% ADNB, where a membrane could be observed that had completely adhered to the particles and filled the pores. SEM images of the interior of an aggregate are shown in Figure 11. Only a small amount of polymer emulsion had reached this zone, which was insufficient to form an integrated membrane structure and instead just formed chains. The chain bonding was weak compared with the membrane structure. Because of the excellent elasticity of ADNB, the integrated memb  
Figure 10: SEM images of the aggregate surfaces: (**a**) treated with 2% ADNB; (**b**) treated with 5% ADNB. Figure 9: Illustration of the infiltration and stabilization mechanism of the polymer emulsion on the surface of the soil aggregates: (**a**) untreated aggregate; (**b**) polymer emulsion infiltrated the soil; (**c**) polymers gathered on the surface; (**d**) soil-polymer matrix formed after water evaporating. and/or filled in soil pores played a major role in protecting the aggregates from collapsing when immersed in water. The particle-polymer matrix significantly improved the water stability. When a modified aggregate was immersed in water, the water molecules could not immediately penetrate into the interior because of the stabilized shell. The water first completely infiltrated the membrane that coated the soil particles and/or filled the pores and then further entered the interior of the aggregate. During this process, the aggregate remained stable in the water. Thereafter, the aggregates would become saturated with water, and swelling of the soil particles would then generate an inner expansion pressure (Figure 12a).