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What Is Clamshell Dredging?

Your Questions Answered

In the world of dredging, there are a lot of tools and machines that can be used. To most people, these are just large pieces of equipment, and one looks much like another. To the expert, however, these machines have specific purposes. One important machine is for clamshell dredging, a unique process with specific areas of application.


What Is Dredging?

This is the act of removing sediment and debris from the bottom of a body of water, including harbors, lakes, rivers, and ponds. This process is necessary because as sedimentation (sand and silt) washes downstream or from shore, it gradually fills in these areas.


The purpose of dredging is to ensure that navigation channels, berthing areas, or anchorages are the right depth to allow ships and boats to safely pass through them. Since many ships and boats bring in imported goods from around the world, they are an important part of the local and global economy and need to move easily to get to their ports and destinations.


Another role of dredging is to reduce exposure to contaminants and to ensure that those contaminants don't get into other bodies of water. This process protects fish, wildlife, and humans. The disposal of the sediment that is taken out of the body of water is managed and accomplished by local, state, and federal governments. In some cases, private entities such as port authorities will also be involved in this task.


What Is Clamshell Dredging?

The machines used in the dredging process are called dredges. Clamshell dredging is done by a particular dredge that has a self-filling and discharging scoop or bucket. It is attached to a crane, which is also where the engine and controls are also located. Sometimes, this is also referred to as “grab dredging.”


A clamshell dredge will have a rotating cab or a fixed A-frame that is mounted to a barge. A driver controls the system and uses a bucket that is lowered into the water to grab, or clamshell, the sediment. The term clamshell refers to the action, which looks a bit like the two sides of a clam's shell clamping together.


After the bucket closes or clamshells around the material, the bucket is hoisted out of the water using the crane and cables and then deposited onto a barge where it can be taken for disposal.


This different from backhoe dredging, which uses a backhoe to dig out the sediment, or suction dredgers, which basically act like a giant vacuum. Clamshell dredging is normally done with equipment that is stationary and fixed at the excavation site with spuds or anchors. In some cases, the cranes can be placed on self-propelled hoppers which transport the materials for disposal rather than placing them on a barge.


Are There Advantages to Clamshell Dredging?

The advantages of using a clamshell dredger is that they can be used in fairly deep waters, they are great for precise spot dredging, and they can remove isolated areas above grades along dock walls, in the corners of docks, and in the navigation prism.


Clamshell dredgers can be used to take out cobbles, sands, clay, gravel, and occasionally broken rock. They aren't particularly helpful in fine silts because these have a tendency to slide out of the bucket. However, even this can be overcome with specially sealed buckets when necessary.


Where Are Clamshell Dredgers Used?

Large clamshell dredges are typically used for bulk dredging, but smaller ones can be used for special jobs that include harbors that are hard to access, for sand and gravel mining, and in moraine areas where large rocks may be expected.


Looking for a Clamshell Dredger?

If you have any clamshell dredging needs, then contact United Dredging. We have the skill and equipment to help with any dredging project you might have.


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