On Porous Bonded Residual Soil in Natural and Dynamically Compacted States Through Plate Load Tests

Aspects related to differences in the behavior of plate load tests (PLT) bearing on highly porous, lightly bonded weathered clay in its natural structured and dynamically compacted states are addressed in this paper. Dynamic compaction is a ground improvement technique involving the release of a substantial weight from an elevation to the ground. The studied bonded residual soil presents specific characteristics, such as high stiffness at small deformations due to natural cementitious bonding, high porosity (higher than 50%), and high hydraulic conductivity (about ${10}^{-5}\mathrm{m}/\mathrm{s}$). Due to dynamic compaction, soil stiffness is reduced at small strains from the breakage of cementitious bonds caused by the impact of the heavy weight. Additionally, porosity is reduced from 55% to approximately 49%, and the degree of saturation is increased from approximately 73% for the natural soil condition to approximately 90%. The angle of internal shearing resistance (${\varphi }^{\prime }$) increased from 30.5° to 35.4°. The applied pressure-displacement results of PLT that rests on natural and dynamically compacted soils were assessed. The young modulus from PLT ($E_{field}^{\prime }$) for the naturally bonded state is higher than $E_{field}^{\prime }$ of PLT on a dynamically compacted state for displacements up to approximately 20 mm. This phenomenon occurs because the latter displayed the bond damage due to tamping that overcame the effects of porosity reduction. In contrast, at large displacements, the effects of the soil porosity reduction caused by heavy tamping are more effective than the effects of bond breakage that ends up increasing the bearing capacity of the PLT from 215 kPa on naturally bonded soil to 297 kPa on dynamically compacted soil.