Experimental study on scouring by submerged pulsed waterjet vertically impinging on cohesive bed

To enhance the efficiency of marine structure installation and river dredging projects, meeting elevated standards, an experimental investigation on the vertical submerged pulsed waterjet scouring cohesive beds was conducted. This study involved the design of a specialized experimental apparatus and the exploration of various factors influencing scour performance. Employing different proportions of kaolin and quartz sand to replicate cohesive beds with varying permeability, the impact of jet pressure, standoff distance, scour time, soil properties, and nozzle structure parameters on scour performance were studied. The experimental findings reveal distinct characteristics of the pulse waterjet's scouring effect. Notably, the scour hole's size along the water jet direction surpasses that in the radial direction, forming a circular erosion hole. The relationship between scour hole depth and variables such as scour time, jet pressure, and standoff distance exhibits distinct patterns: logarithmic, linear, and quadratic, respectively. Higher quartz sand content strengthens the cohesive bed's shear strength, reducing its susceptibility to scour. Through an orthogonal test, the optimal parameter for submerged pulsed waterjet scouring cohesive beds as A1B2C3D2, that is, the standoff distance of 15 mm, jet pressure of 3 MPa, oscillation cavity length of 5.2 mm, and downstream diameter of 1.8 mm. The hierarchy of factors influencing scour performance is established as jet pressure, standoff distance, downstream diameter, and oscillation cavity length. Notably, pressure significantly affects scouring performance, while standoff distance, oscillating cavity length, and downstream diameter exhibit no obvious impact. The study contributes to understanding the interaction mechanism between pulsed waterjets and cohesive soil, offering substantial potential for applications in engineering, including dredging and anchor extraction from sediments. •The mechanism of vertical submerged pulsed jet scouring cohesive bed was studied.•The influence of various factors on the scouring performance is summarized.•The size of the scour hole in the jet direction is larger than the radial direction.•The optimal construction parameters are obtained by orthogonal test.