Abstract: Hydraulic jet trenching technology has been widely used in submarine pipeline and optical cable embedding engineering. However, jet trenching construction in stiff clay is difficult. In order to elucidate the mechanism of soil breaking, the physical simulation experiment of submerged vertical jet trenching was carried out. During the process of soil breaking, it is found that there are some differences between the development characteristics of scour hole in soft clay and stiff clay. Shear-compression stress is the main factor of soil breaking in stiff clay and the breaking mode in stiff clay can be explained by the Prandtl foundation ultimate bearing capacity theory. Based on this, the model of jet to break hardpan is established, and the diameter of hole's neck is proposed to replace the diameter of scour hole as a prediction index.

Key words: submerged jet, trenching, bearing capacity