Gu, L.; Ni, F.; Xu, L., and Li, Z., 2018. Determining the threshold pressure of clay-cutting by a mobile jet for coastal construction.Trailing suction hopper dredgers (THSD) are widely used in channel excavation and coastal construction projects. In such projects, clay is a common soil that is difficult for the drag head of THSDs to dredge. Jet-cutting using a mobile jet is often adopted to improve the efficiency of the drag head, since it can create grooves into the clay surface and reduce cutting forces for the drag head. The jet pressure is an important factor for jet-cutting, so it is necessary to accurately grasp the threshold pressure of clay-cutting by the mobile jet. In this paper, clay samples with three different strengths (undrained shear strength Su = 16 kPa, 35 kPa, and 51 kPa) were prepared, and clay-cutting experiments using a mobile jet were conducted. The effects of parameters such as the nozzle diameter, the moving speed, and the jet pressure on the cutting results were investigated, and the cutting depths under different jet pressures were measured. The threshold pressure was measured, and the cause of clay failure under jet-cutting was analyzed. The results show that the nozzle diameter and the moving speed changed the cutting depth via the exposure time during the clay-cutting, and that the cutting depth increased linearly with cumulative cutting time. The threshold pressure was independent of the jet diameter and moving speed and only increased linearly with the undrained shear strength of the clay. In the cutting process using a mobile jet, shearing slippage was the main failure mode of clay, and the jet was only able to effectively cut the clay when its pressure was higher than the ultimate bearing capacity of the clay bed.