Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Experimental study on cutting hard soil with new hob draghead of TSHD
Shuai Jiang, Jifu Yin, Zhongwei Zhou*, Minhua Shu

National Engineering Research Center of Dredging Technology and Equipment, Shanghai, China

ABSTRACTINTRODUCTION

As the main construction vessel of dredging project, the TSHD (trailingsuction hopper dredger) has low efficiency when dredging hard soil. It
is because that the cutting depth of the draghead is limited, theconcentration of suction slurry is low. Therefore, researchers propose a
new draghead scheme, which changes the traditional mode ofhorizontal movement of single row of teeth into the mode of rotary
cutting with multiple rows of teeth, which can greatly increase thecutting depth and dredging efficiency. At the same time, the new
cutting method has also brought great changes to the structure andprocess parameters of the whole draghead. But in fact, researchers havelittle understanding of the cutting mechanical behavior and thecorresponding process parameters, and the hob draghead is far fromachieving field application. Through laboratory experiments, this paper
analyzes and grasps the influence law of several key factors such as soil
cutting depth, hob rotation rate and moving speed on hob cutting effectwithin the range of construction parameters. The experiment results
show that the deeper the hob is embedded in the soil, the greater theforce on the rake teeth and the power consumed. The increase of hobrotation rate can greatly reduce the force on the rake teeth, but the totalrequired power increases a little. The lower the rotation rate, the larger
the block or slice after soil failure, and the greater the probability oflarge instantaneous cutting force. Reducing the moving speed canquickly reduce the cutting torque and power. Although increasing thecutting depth, hob rotation rate and reducing the ship forward speed caneffectively improve the dredging efficiency of the draghead, it is worth
noting that these factors are limited by the equipment and operation ofthe suction dredger. For example, the TSHD needs a certain speed tomaintain its heading stability, and the power of the ship's main engine
needs to be reasonably distributed. Therefore, the research anddevelopment of the new hob draghead is a complex and systematic
research work. The research results of this paper can provide importantreferences for the structural design and the determination of processparameters of the new draghead.

The TSHD (Trailing Suction Hopper Dredger) is the main operation
ship of dredging engineering, which plays an important role inreclamation of land from the sea, channel dredging and other projects.
As one of its most key dredging machines and tools, the draghead is
directly in contact with the seabed to excavate soil and transport it to
the cabin, which affects the operation efficiency and dredging capacityof trailing suction hopper dredger. Taking the California draghead as anexample, its structure is shown in Fig. 1. The seabed soil is excavatedmainly through the horizontal movement of a row of rake teeth
installed at the draghead bottom. The cutting angle of the rake teeth canbe adjusted through the movable cover, and high pressure water jet is
equipped to pre-cut the soil.
During the dredging of the draghead, on the one hand, when the
draghead moves forward with the rake pipe and hull, the high-speed
water flows through the gap between the bottom edge and the soil
bottom to wash the soil down and enter the draghead. On the other
hand, the high-pressure water will be sprayed from the nozzle on the
draghead to disperse the soil, and then the soil is cut by the teeth. The
soil is suspended by the interaction of washing and cutting, and then thesuspended slurry will be suctioned by the vacuum pressure difference
generated by the slurry pump, and is transported to the slurry tankthrough suction rake pipe. Among them, the cutting process directly
determines the ability of excavating the soil. For the soil with low
strength, the traditional draghead can easily deal with it. However, for
high-strength hard soil, such as dense fine silt or hard clay, thetraditional draghead often has low output and high cutting resistance,
resulting in low dredging concentration and efficiency. It is difficult fora single row of rake teeth to maintain a large penetration depth duringtranslation cutting, and the cutting resistance also increases
significantly. At the same time, hard soil are often broken into large
pieces during excavation, which are easy to block rake head grille andmud pump. Although the output of the whole draghead can beimproved by increasing the jet pressure, its effect of the rake teeth isstill very limited. Therefore, a new challenge is posed to the draghead,
and it is need to be improved urgently.

KEY WORDS: Experimental study, TSHD, new hob draghead,cutting hard soil

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