This thesis provides an advanced interpretation procedure to assist site investigations of offshore oil/gas explorations, where layered soil profiles are frequently encountered. There are three penetration probes studied: T-bar, ball and cone penetrometers. Through centrifuge image analysis and large deformation finite element analysis, the soil flow mechanisms around the probes are revealed. This revelation has prompted new interpretation frameworks for the penetrometers, which is capable of interpreting in-situ soil strength more accurately than existing methods. The development can provide better soil parameters for safer and more economical offshore foundation designs.