This study presents a soil parameter validation procedure using numerically simulated CPTu, employing GPFEM to simulate the Piezocone (CPTu) test under undrained conditions in soft estuarine clay. Soil parameters are derived from high-quality undisturbed samples collected at the NFTF in Ballina, Australia. The main objective is to improve confidence in parameter determination by comparing simulated CPTu results with in-situ measurements. Three distinct simulation depths within the same soft clay layer are analyzed, with results showing good agreement between simulation and measured data at all depths. A sensitivity analysis is also conducted, addressing uncertainties in parameter determination. The study demonstrates the effectiveness of this approach in enhancing constitutive parameter determination, especially for projects with limited or unavailable high-quality undisturbed samples.