Vibro stone column installation and its effect on ground improvement

Results of installation accompanying measurements of the in situ stresses, the ground stiffness and the ground surface vibrations in various test fields are presented. Following the installation, the stone columns are subjected to group loading whilst the instrumentation remains active including load pressure cells and settlement transducers. The results show significant alteration of the stress state and the soil stiffness during penetration of the depth vibrator and the subsequent stone column installation. Two major effects can be distinguished: the displacement of the ground due to the creation of the stone column body and the ground vibration with associated changes within the soil due to the movements of the depth vibrator. The results of the measurements are used to model the installation effects in numerical analyses using the finite element method. Comparison between the numerical results and the findings of the measurements as well as the load test results are used to calibrate this numerical model. Finally parametric studies are undertaken to estimate the additional improvement effect of the installation process on the total ground improvement factor for vibro stone column measures.