In this thesis research is presented on the influence of multiple thin soft layers on the cone resistance and an attempt has been made to develop a correction factor from numerical and physical models. The presence of thin layers causes difficulties with determination of the liquefaction potential of sand deposits containing thin clay layers using cone penetration testing (CPT) data, including the cone resistance. Understanding the behaviour of the cone resistance in layered deposits and correcting the cone resistance is believed to help finding a solution. In this research numerical models are presented to simulate the cone resistance in deposits with multiple layers. Using numerical models a range of correction factors is determined for different soil compositions, concluding that correction factors for the cone resistance depend mainly on the ratio of characteristic resistances of sand and clay. Physical modelling has been performed for validation of the numerical models and for correction factor determination. Layered samples were artificially built and tested using a cone, which besides measuring cone resistance also contained a friction sleeve and an u2 pore pressure transducer. Cross-sections have been made of tested samples to obtain an indication of the penetration process. Since a limited amount of test results were obtained complete validation was not possible in this research, although the available test results could considerably well be simulated using the numerical models. Feasibility of performing tests on layered samples and obtaining results has been demonstrated.