Simplified and modified algorithms for dynamic compressive stress in mixed soil-rock fills under dynamic compaction

Dynamic compaction is one of the most convenient methods of ground improvement. It is crucial to reasonably analyze additional dynamic compressive stress on the compacted soil in practice. The typical mixed soil-rock fill in Chengdu plain is investigated in this study. The vertical dynamic stress at different depths in the soils subjected to dynamic compaction with an impact energy of 4 000 kN center dot m is tested in situ. Considering the difference between the observed results and those using the existing calculation methods, simplified and modified algorithms for the dynamic compressive stress are developed. On the one hand, parameter sensitivity analysis and linear regression analysis are conducted to simplify the existing complicated formula via eight parameters characterizing the surface impact stress including the mass of rammer, fall height, radius of the rammer, soil density, dynamic shear modulus, Poisson's ratio, damping ratio, as well as impact velocity loss rate of the rammer. On the other hand, based on the pseudo-static method, a modified formula of the vertical dynamic stress at different depths of the soil is provided via introducing a transfer index into the elastic static stress dispersion equation, and the modified formula can be employed to analyze the effective impact depth. The example of the mixed soil-rock fill from the field test demonstrates a transfer index of 1.673 57 and an effective impact depth of approximately 8.0 m..