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Dredging Methods and Equipment

John Huang, Ph.D., PE and John Poullain, PE

This four-hour online course provides general guidelines and design considerations used for dredging operations, selection of dredging equipment and disposal of dredged material. The course provides an overview of the types of equipment, their advantages and limitations, the required tests, and the dredging techniques employed. Concerns and precautions for the prevention of adverse effects on the environment and animal habitats and utilization of dredged material for beneficial disposal are considered. Remedial actions and activities performed at the work sites must comply with federal, state and local regulations to protect water quality, fish and animal habitat.

Dredging basically has two functions, to obtain material, to excavate holes and to provide greater water channel depths. There are several methods of excavation, which include cutter head suction and hopper suction dredges and mechanical excavators. Cutterhead dredges have suction pipelines to pump the dredged material into disposal areas, barges or hopper barges for longer distance transportation. At least one cutterhead dredge in the US is electrically powered via power cables from shore side substations. The all electric dredge has a 34-inch diameter suction pipeline and is powerful enough to pump very long distances without using booster pumps, one of the longest discharge distances was about 18,000 feet. Another type of dredge, the hopper suction dredge, drag suction heads along the ocean floor or marine area to be excavated. The dredge material is deposited in the hopper and transported to disposal areas, making them a good choice for long distanced disposal areas, which usually requires pumping assistance with booster pumps.

Channel excavation may require blasting to break rock masses into more readily excavatable strata. There are a few excavators, which have enough power to breakup rock without blasting; one of the biggest has perhaps 370,000 lbs. of breakout force. The bucket teeth are used to break into rock gaps in order to reduce a rock mass to smaller pieces for ease in removal and loading. They are similar to the land based excavators and have hydraulically controlled booms and 26 cu yd buckets.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

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