In this study, the excavation process of a low pressure vertical impinging jet in cohesive soil has been investigated. Mass flow excavation is a hydraulic, low pressure, subsea excavation method whereby a large volume flow is applied to the seabed through which the seabed is eroded, and the soil is transported. The erosion process of a cohesive soil by impinging jets depends on many variables (e.g., jet flow velocity, standoff distance, grain size, undrained shear strength). The erosion processes, especially for dynamic pressures of lower than two times the undrained shear strength, are not fully understood. It is still unknown what the influence of different soil and jet parameters are. As a result, it is still unknown what the expected scour rate will be during a mass flow excavation process of cohesive soils. The goal of the research is to quantify and be able to predict the production of a mass flow jet on cohesive soils. For this purpose, the relevant parameters of cohesive soil erosion are investigated, and fluid velocity profiles of the jet are related to clay bed failure mechanisms. Special attention is put on the effect of the consolidation coefficient on the erosion process. Based on literature and experimental research, different soil failure mechanisms have been investigated. The main result of this study is a relation between the main jet and soil parameters, and the erosion velocity development.