The erosion process of cohesive soil due to a submerged inclined water jet

Abstract

This thesis investigates the erosion process of cohesive soil due to a submerged, moving, inclined water jet. This study provides a visualization and description of the failure mechanics of cohesive soil due to a submerged inclined water jet and develops a new equation for estimating the erosion process of cohesive soil while including the angle of the water jet as a parameter. Figures providing support to this new equation are also provided in Chapter 7. The primary variables tested are jetting angle, stand-off distance, forward velocity, and jetting velocity.

The study is guided by two primary research objectives. First, to visually and descriptively understand the failure mechanics of cohesive soil subjected to a submerged inclined water jet. Second, to develop a method of predicting the erosion process of cohesive soil, considering variable jet angles, stand-off distances, forward velocity, and jet velocity of a submerged inclined water jet.

Experimental testing was conducted in the "Dredging Lab" of Delft University of Technology. The experiment involved eroding cohesive soil blocks using half of a circular nozzle placed along the wall of a flume. This nozzle configuration allowed for the nozzle to be visible during testing. I designed several half nozzles that were tested in a flume provided by TU Delft. Nozzles with a variety of nozzle diameters were designed to have either a 25, 45, 65, 90, 115, 135, or 155 degree jetting angle. Seventy-two clay blocks with a known undrained shear strength were used as the cohesive test soil, allowing for immediate replacement after each test. Detailed experimental procedures are outlined in Section 5.3, offering insights into the design and execution of the tests.

The data analysis provides evidence that the jetting angle has a notable impact on the erosion process of cohesive soil. This includes a “deflecting jet” failure mode, the formation and prediction of the sediment plume, and the estimation of the erosion cavity depth. The failure mode of the soil can be seen in Section 5.5 and data analysis figures are provided in Chapter 6. Section 7.1.2 provides a new estimation for the erosion depth of cohesive soil using an inclined water jet (Equation 7.17). This study contributes to our understanding of cohesive soil erosion and methods of estimating erosion processes. The findings emphasize the crucial role of the jetting angle and provide a foundation for future research aimed at refining erosion prediction models and exploring additional parameters influencing the process. Practical applications may include improved design considerations for projects involving water jet erosion such as deep-sea mining, water injection dredging, trailing suction hopper dredgers, as well as other dredging processes involving water jetting.