## 1 Introduction  
Soil surface treatment can improve soil erosion resistance, strength, and stability, which is of great significance in soil-water conservation and dust prevention. It is practical to improve the soil surface using physical methods (such as covering dust-proof net) and using chemical substances (such as cement, lime, fly ash, gypsum, surfactant, polymer, asphalt products, waterborne polyurethane, etc.) [1]. In recent years, the application of MICP in soil improvement has attracted extensive attention [2]. MICP technology mainly uses bacteria to produce urease to the hydrolyze urea and generate CaCO\({}_{3}\) to achieve cementation and reinforcement. Although MICP technology presents greater implementation complexity due to the use of living organisms, and has a higher cost compared with traditional technologies [1], it has broad application prospects in soil improvement, concrete crack repair, erosion prevention, cultural relic restoration, and heavy metal pollution control [3; 4; 5; 6; 7] due to its environmental friendliness and sustainability [8; 9]. MICP can effectively cement soil particles together and improve the performance of soil. [PERSON] et al. [10] used surface filtration technology to place bacteria and cementation solution. Under high permeability, bacteria and cementation solutions could be used alternately many times to fix bacteria in a column of more than 1 m, and the homogenization of the improved sand column reached a reasonable degree. [PERSON] et al. [11] used MICP technology to carry out a reinforcement test on a 100 m\({}^{3}\) large sand foundation, which effectively improved the bearing capacity of the sand foundation. Moreover, soil surface could also be reinforced by MICP. [PERSON] et al. [12] used a mixture of calcium salts, urea, and bacterial suspension to make a crust on the surface of the sandy soil, which reduced the permeability of the sand layer from 10\({}^{-4}\) m/s to 16 \(\times\) 10\({}^{-7}\) m/s (14 mm/d). [PERSON] et al. [13] used a surface spraying method and an MICP technique to surface treat a series of model slopes prepared by different grades of sand, which effectively reduced the rainfall erosion of sandy slopes. [PERSON] et al. [14] applied MICP treatment to five groups of soil slope model samples, and showed that MICP treatment is an effective method to control the surface erosion of clayey soil by analyzing the soil erosion pattern and soil loss rate. [PERSON] et al. [15] studied the application of the MICP technique in different grades of silica sand and carbonate rocks, determined the optimum reagent concentration, and investigated the variation pattern of shear strength and resistance to wind erosion after a number of different treatments. The wind tunnel tests showed that the treated crustal sands could remain stable at a wind speed of 20 m/s. The desired result of surface reinforcement should be a significant increase in soil strength within the shallow layer [16]. However, the existing MICP treatment solutions, such as grouting or surface penetration, may be difficult to achieve this desired treatment due to their higher permeability, which is more suiTable for deeper treatment. Due to the large permeability of the soil to be treated, existing studies generally use micro-dose injection of MICP solution in order to make the MICP treatment solution and to more precisely reinforce the shallow soil. In addition, in order to achieve the desired treatment effect, the MICP solution is generally infiltrated several times. [PERSON] et al. [17] injected the bacterial solution and the cementing solution into the soil 18 treatments. In the experiments of [PERSON] and [PERSON] et al. [18], they also made multiple infiltrations to reach the target due to the large permeability. Materials such as hydrogels (xcan, ganlan) or polyvinyl alcohol (PVA) can reach such shallow depths of cementation, whereby the crust is formed by cementing the shallow layers to improve the soil surface [19]. [PERSON] et al.