Large-scale test of sleeve valve pipe grouted overwet subgrades

Due to the intense capillarity action on low-liquid limit silt subgrade, the subgrade is often overwet. The technology of sleeve valve pipe grouting is an effective reinforcement method of the overwet subgrade. However, there are limited studies on the reinforcement mechanism and its effects. In this study, four large-scale subgrade models were set up. Distributions of moisture content and physical mechanical indexes of soil in different silt subgrades were analysed. Integral stiffness and deformation characteristics of the subgrades were studied by cyclic step loading tests. The subgrade models were excavated after tests to see the spreading pattern of the grout slurry. The reinforcement mechanism of the sleeve valve pipe grouting was analysed based on Vesic's cavity expansion theory. The results indicate that the integral stiffness and stability of the subgrade decrease due to the capillary action. The vertical plastic deformation of the wet subgrade rapidly increases with the increase in vehicle load. Sleeve valve pipe grouting produces bottom-expanded micropiles, and also horizontal reinforcement layers, which can block the capillary water from rising and form a space frame with the bottom-expanded micropiles to bear the load with the soil together. This increases the subgrade stability, and the reinforcing effect is more significant than with the traditional grouting technology.