A numerical study addressing CPTu inversion in organic soils containing gas

¹ Department of Civil and Environmental Engineering, Politecnico di Milano, Milano, Italy
² Department of Geoscience and Engineering, Delft University of Technology, Delft, The Netherlands

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Soft organic soils often contain gas pockets generated by the chemical decomposition of organic matter. The gas content fluctuates seasonally with temperature and barometric pressure, can alter the soil mechanical response and complicates the interpretation of cone penetration test (CPT) results. The influence of gas on CPT response remains poorly understood, resulting in a critical gap in knowledge that can potentially lead to either unsafe or overly conservative engineering design. This study starts investigating the role of gas content on CPT results, using a numerical approach based on a coupled hydro-mechanical particle finite element formulation. In the analysis, the gas volume fraction is incorporated by adjusting the compressibility of the fluid that saturates the pore space. The findings demonstrate how accounting for gas content enables more accurate interpretation of CPT results and more reliable estimation of shear strength. A strategy for simultaneously estimating gas content and undrained shear strength in organic gassy soils using CPT data is proposed. The study further suggests that both the gas volume fraction and the cone factor can be theoretically inferred from the spatial distribution of pore pressure, providing a practical means to enhance design safety and cost-effectiveness in soft soil engineering.