# Experimental Study of Erosion Prevention Model by Bio-Cement Sand
## 3 Results and Analysis  
### Penetration Test Results and Analysis  
In the absence of initial reinforcement, subsequent applications were conducted three and six times, after which penetration resistance was assessed at eight designated points on the sand surface of the sandbox mold. Sand samples from these measuring points were extracted using a ring knife and subsequently analyzed in the laboratory, with a primary focus on quantifying both the average thickness and calcium carbonate content within the cemented body obtained via this method. The results of these tests are summarized in Table 1 below. Figure 7 illustrates the variation in penetration strength across a sandy soil slope reinforced through microbial spraying at different frequencies of application. As shown in this figure, there is a pronounced increase in strength at each measuring point following three rounds of reinforcement, with nearly all points demonstrating significant enhancement after six rounds. Importantly, this increase exhibits notable non-uniformity; specifically, strengthening occurs more rapidly along the slope boundary compared to slower rates observed within its central region treated by microbial spraying. After six applications of reinforcement, it was determined that strength augmentation near the edge of the model slope is twice that recorded for its middle section. The maximum penetration resistance achieved after three reinforcements reached 515.55 kPa, while after six reinforcements, it peaked at 1106.66 kPa. Therefore, reinforcing sandy soil slopes through microbial spraying markedly enhances their penetration strength--exhibiting lower values centrally, while higher values are noted peripherally. The penetration strength exhibits a positive correlation with the number of reinforcement applications. However, the rate of increase in penetration strength diminishes as the degree of reinforcement escalates. This observation suggests that the sample can attain a higher strength after undergoing three rounds of reinforcement. Cemented sand adjacent to the test point was extracted using a ring knife, and the thickness of the hardened shell was measured. The weight of calcium carbonate was quantified via a drying method. Subsequently, the calcium carbonate content in the sample was calculated by dividing the dry weight of the sand sample packed within the ring knife box without reinforcement. The maximum calcium carbonate content achieved after three reinforcements reached 9.16%, while that attained after six reinforcements increased to 12.24%. The maximum cementation depth recorded following three reinforcements was 9.18 mm, whereas for six reinforcements, it measured 13.23 mm. A dense cementing  
Figure 7: Spatial distribution characteristics of penetration resistance in sand models with different reinforcement degrees. stratum constituted by calcium carbonate deposition was established on the sandy soil slope reinforced through microbial spraying. The depth of cementation ascended in line with the augmentation of reinforcement instances. Owing to the continuous infiltration of microbial solution and cementing fluid into the soil, calcium carbonate precipitation was perpetually generated and accumulated. The study of the effects of microbial spraying on the reinforcement of sandy soil slopes indicates that the distribution of calcium carbonate, along with reinforcement depth and penetration resistance strength, demonstrates considerable variability. This phenomenon can be attributed to several factors. Firstly, achieving uniform penetration of microbial slurry and cementing fluid via a manual watering can presents significant challenges, often leading to an uneven distribution of calcium carbonate precipitates that adversely impacts the consistency of penetration strength. Secondly, the stability of sand models reinforced through microbial spraying is intricately linked to soil characteristics.