Abstract: The explosion replacement method is an effective treatment for weak soil layers exceeding 15 m in thickness. To investigate the effect of explosive deposition depth on treatment efficacy, model tests involving silt blasting were conducted, and vane shear tests were performed using an automatic cross shear apparatus. The effects of explosive deposition depth on the undrained shear strength and water content of silt were examined. Additionally, the soil microstructure before and after blasting at various depths was observed using a scanning electron microscope. The results indicated that blasting disrupted the soil structure around the explosion point, increasing the void ratio and causing a sudden drop in undrained shear strength, thereby forming a blasting disturbance zone. The soil outside the disturbed zone was compacted, resulting in increased undrained shear strength and forming a blast-compacted zone. After blasting, soil water content decreased; the farther from the explosion center, the more significant the decrease. When the explosive deposition depth was 0.3 times the soil layer thickness, the reduction in undrained shear strength was most significant at about 27%, and the disturbed zone was largest at approximately 19.2d (where d is the explosive diameter), making the explosion most effective. Therefore, there exists an optimal deposition depth of the explosive, which makes the best explosion treatment effect and the largest range of disturbed soil. And, the range of blasting disturbance can be determined by undrained shear strength. The results of the study can provide technical support and reference for the design of explosive deposition depth in related projects.

Key words: explosion replacement method, explosive deposition depth , vane shear test, undrained shear strength, water content, void ratio