Experimental study on the diffusion characteristics of cement grout in sandy considering soil unloading and grouting condition effects

Grouting method is widely used in fields such as foundation reinforcement and building rectification. However, there is currently a lack of systematic research on the impact of grout diffusion on the stress field and grout reinforcement range within the unloaded soil under different grouting conditions. This paper conducts a series of grout diffusion experiments in sandy soil using a self-developed three-dimensional grouting system, and systematically analyzes the influence of water-cement ratio, grouting pressure, grouting volume and soil unloading degree on the stress increment in soil, the shape of grouting body, the grout diffusion radius and the grout reinforcement ratio. The results show that the most significant changes in soil internal stress caused by the slurry are located at the same burial depth plane as the grouting port, followed by the soil above the burial depth of the grouting port, and the soil below the burial depth of the grouting port has the smallest changes in soil internal stress. The average attenuation amplitude of the average stable stress increment in the soil after grouting is about 30% compared to the average peak stress increment in the soil. The average stress increment in the soil shows a trend of first increasing and then decreasing with the increase of water-cement ratio and grouting pressure, while the average stress increment in the soil increases with the increase of grouting volume and soil unloading ratio. The overall shape of the grouting body under different conditions is ellipsoidal, and the planar diffusion shape formed by the side wall grouting is approximately elliptical with a “large top and small bottom”. The equivalent diffusion radius of grout increases with the increase of grouting volume, soil unloading degree, and water-cement ratio, while it shows a pattern of first increasing and then decreasing with the increase of grouting pressure. For the average soil stress increment and the equivalent grout diffusion radius, the grouting volume exhibits the greatest influence within the tested parameter intervals, while the soil unloading degree shows the least effect.