Side post-grouting bored-pile foundations are widely used in geotechnical engineering. However, few studies have focused on analyzing the shear behaviour of soil and concrete while considering the grouting process. A total of 48 groups of self-developed, large-scale direct shear experiments were conducted to investigate the shear behaviour of sand-concrete interface with side-grouting, focusing on the effect of soil stress unloading and the on-site roughness measurements of bored pile. The influence of the grouting volume V, unloading rate α and interface roughness R on the shear behaviour are discussed, and the grouting modes and shear band deformation are investigated. The experimental results indicated that the grouting volume has a limited effect on improving the shear strength, and an optimal grout quantity will exist in post-grouting engineering. In addition, the unloading has a non-negligible influence on the grouting modes.
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