Earth-Moving Machines, equipment used in heavy construction, especially civil engineering projects, which often require the moving of millions of cubic meters of earth. The removal of earth or material from the bottoms of bodies of water is performed by dredges.
The primary earth-moving machine is the heavy-duty tractor, which, when fitted with endless tracks to grip the ground and with a large, movable blade attached in front, is called a bulldozer. Bulldozers are used to clear brush or debris, remove boulders, and level ground. A scraper is a machine that may be pulled by a tractor or may be self-powered. It consists of a blade and a box or container.
Dirt is scraped by the blade into the container; the dirt may then be released so as to form an even layer of a predetermined thickness, or be carried off for disposal elsewhere. Scrapers are used to level and contour land, as in road construction.
Somewhat similar to scrapers are graders, self-propelled, wheeled machines with a long, inclined, vertically adjustable steel blade. Graders are primarily finishing equipment; they level earth already moved into position by bulldozers and scrapers.
In excavation, a grader is a precision finishing vehicle for final shaping of surfaces on which pavement will be placed. Between its front and rear wheels a grader carries a broad mechanically or hydraulically controlled blade that can be extended from either side. Either end of the blade can be raised or lowered. Graders may be used for shallow ditching, but most models are used to assist other earth-moving equipment and to smooth roads, fills, and cuts.
Lightweight tractors fitted with wheels in place of tracks are used for comparatively light construction jobs. Equipped with a backhoe, which is an open scoop attached rigidly to a hinged boom, such a vehicle can dig shallow trenches; equipped with a front-end loader, a scoop shovel affixed to the front of the tractor, it can lift and carry gravel, stone, sand, and other construction materials.
Draglines and power shovels are the primary forms of excavation equipment. A dragline is fitted with an open scoop supported from the end of a long boom by a wire cable. The scoop is dragged along the ground by the cable until it is filled with earth, which is then dumped elsewhere.
Draglines are used primarily to excavate deep holes. Power shovels are fitted with buckets called clamshells, which dig into the earth and shovel it up. The bottom of the clamshell opens to dump the dirt into a truck for removal.
