Effect of Rotational Speed on the Reinforcement of Cement–Soil Mixing Piles in Building Foundation

In soft soil areas, cement–soil mixing piles are widely employed as a building foundation treatment measure, and their construction parameters directly influence pile uniformity and the stability of foundation reinforcement. However, visual and quantitative methods to verify on-site improvement effects are currently lacking. This study aimed to improve the mixing uniformity between jet media and soil layers and proposed a quantitative evaluation method based on numerical simulation and image recognition. Taking the silty soil in the Nansha area in Guangdong Province, China, as the research object, combined with flow tests and discrete element simulations, an experimental simulation based on a linear model of adhesive rolling resistance was established. First, the entire process of the wet water spraying soil mixing method and visualizing particle behavior was simulated. Based on the Danckwerts mixing index, image recognition technology was applied to quantify the uniformity of cement–soil mixing at different rotational speeds. The simulation results revealed that increasing the rotational speed within a certain range (0–100 r/min) significantly improved the uniformity of cement–soil mixing by 33.3%. However, increasing the rotational speed still further (100–200 r/min) resulted in only a 15.8% improvement. Furthermore, excessive rotational speed caused a significant loss of cement within the designed diameter of the pile. Second, based on the cement retention rate inside the pile, a speed balance range suitable for the working conditions of this study was obtained. A good balance was achieved between the effective cement content inside the pile and the uniformity of cement–soil mixing, further ensuring the consolidation effect of the cement–soil pile.