## 1 Introduction  
Clayey slopes are extensively distributed in southern China. The topsoil of a clayey slope is easily washed off by rain due to its loose structure and weak water stability [1]. The loss of topsoil of clayey slopes causes great damage to the environment. With the loss of soil, the clayey slope becomes unstable due to the reduction in soil strength and the lack of reinforcement of plant roots. Traditional methods to protect the slope surface include physical methods and inorganic chemical stabilization methods. Physical methods, such as geotextiles, support the external forces without modifying the soil properties [2; 3; 4; 5]. Although inorganic chemical stabilization methods can greatly improve the engineering properties of soils and have been widely applied [6; 7; 8; 9; 10; 11; 12; 13], the inorganic materials in soils will inhibit plant growth, which is unfavorable to the ecological development of slopes [14; 15].  
In recent decades, non-traditional chemical additives such as polymers, enzymes, ionic substances, lignocellulosic, salts and petroleum resins have been studied [16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. Non-traditional soil stabilization additives consist of a variety of chemical agents that are diverse in their composition and in the ways they interact with the soil. Many researchers have studied stabilization additives to improve the physical and engineering properties of soil to meet the requirements of different engineering practices [28; 29]. Calcium carbide residue (CCR), a by-product of the acetylene production process, was investigated for its ability to improve the engineering properties of clays [30]. A new calcium-based powder additive named SH-85 was used for the stabilization of a tropical residual laterite soil [31]. Xanthan gum was proposed as an environmentally friendly stabilizer that could improve the engineering properties of both low- and high-swelling clays [32]. SS299 was a liquid polymer stabilizer used as a compaction aid or a stabilizer for soil improvement that could increase the unconfined compressive strength of kaolin [20]. Biosolids have been reported to modify the aggregate stability [33]. Polyacrylamide could improve the water stability of clay aggregates [34; 35]. However, these studies were all based on the method of mixing stabilizers and soils.  
An effective way to protect the topsoil of a slope is to spray the stabilization additive onto the surface of the slope without any disturbance. In this case, the stabilization additive should be able to dissolve or disperse in water, unlike organic solvents, which are harmful to the environment. Therefore, it was important to conduct a survey to fully understand the effective infiltration depths of stabilization additives. A new soil additive named aqua-dispersing-nano-binder (ADNB) was applied in this work. Efforts were made to study the mechanism of the water stability of silty soil that had been modified by the polymer emulsion. Various tests were performed with different polymer contents including infiltration tests to obtain the effective depth that the polymer could reach, water stability tests to estimate the water stability of the modified silty clay and scanning electron microscopy (SEM) to analyse the possible mechanism that contributed to the stabilization process. Furthermore, the infiltration mode of the polymer emulsion was identified, and the possible stabilization mechanism was discussed based on the infiltration process and SEM results.