Numerical Simulation of CPTu: A Vacuum Preloading Case Study

Vacuum preloading is an effective method of ground improvement for soft soils. Because of difficulties in obtaining high-quality undisturbed soft soil samples, Piezocone tests (CPTu) are usually carried out before and after the vacuum preloading process. CPTu data collected before improvement are used to determine design soil parameters utilizing various empirical correlations. CPTu data after improvement are used to evaluate the soil improvement results. In this study, CPTu is simulated using the geotechnical particle finite-element method (GPFEM). The numerically simulated CPTu before improvement shows its capability to verify design soil parameters by matching the response of cone tip resistance (qt), sleeve friction (fs), and pore-water pressure (u2) with the in situ measurement. With the same soil parameters, the vacuum preloading process is modeled using a standard finite-element formulation. The settlement prediction from this model shows good agreement with the observed data. The soil in situ stresses and preconsolidation state after soil improvement are then transferred to the GPFEM to simulate another set of penetrations, and again in situ measurements could be reproduced, confirming that the amount of improvement can be anticipated through numerical analysis in early design stages.