All About Clamshells

Clamshells are used primarily for handling loose materials such as sand, gravel, crushed stone, coal, etc., and for removing materials from cofferdams, pier foundations, sewer manholes, sheet-lined trenches, etc. They are especially suited to vertically lifting materials from one location to another, as in charging hoppers and overhead bins. The limits of vertical movement may be relatively large when they are used with long crane booms.

Clamshell buckets are available in various sizes, and in heavy-duty types for digging, medium-weight types for general-purpose uses, and lightweight types for rehandling light materials. Manufacturers supply buckets either with teeth than can be removed easily or without teeth. Teeth are used in digging the harder types of materials but are not required when a bucket is used for rehandling purposes.

The capacity of a clamshell bucket is usually given in cubic yards. A more accurate capacity is given as a water-level, plate-line, or heaped-measure, generally expresses in cubic feet. The water-level capacity of the bucket, if it were hung level and filled with water. The plate-line capacity indicates the capacity of the bucket following a line along the tops of the clams. The heaped capacity is the capacity of the bucket when it is filled to the maximum angle of repose for the given material. In specifying the heaped capacity, the angle of repose usually is assumed to be 45 degrees. The deck area indicates the number of square feet covered by the bucket when it is fully open.

Because of the variable factors which affect the operations of clamshell, it is difficult to give production rates that are dependable. These factors include the difficulty of loading the bucket, the size load obtainable, the height of lift, the angle of swing, the method of disposing of the load, and the experience of the operator.

Each piece of heavy equipment on a construction site is specially suited for a specific task or tasks. The clamshell is not the only piece of excavating equipment available to construction companies by a long shot but when it comes to loose materials like gravel, coal, sand, and crushed stone, the clamshell beats the rest of them hands down.