Earthwork Operations

Pioneering refers to the first working over of an area that is overgrown or rough. This makes the area accessible for the equipment needed for the project.

In pioneering, the operations of clearing, stripping, grading, and drainage are all done essentially at the same time, rather than performed as separate operations. A dozer starts out along a predetermined route and leaves a road behind it. This may be a haul road which trucks and equipment will use in later operations.

Suppose you, as a dozer operator, get the job of cutting a road on the side of a mountain to be used for access to a proposed airstrip or to reach a mountain stream to be developed into a water supply system. Where should you start and how should you proceed? A survey party will stake out the route your mountain road is to follow. Start your road at the highest point possible and let the force of gravity help the dozer.

In clearing on sidehill cuts, cast brush and trees far enough to the side of the road that they will not be covered with the earth. It is even better if you can cast them over the edge with an angle blade of the dozer when the road is cut. When cutting the road, do not watch the grade stake immediately ahead or you will find yourself below grade. Instead, watch the third or fourth stake down.

NOTE

It is better to be above grade and come back and cut down to grade than to be below grade and have to come back and fill.

Clearing is a construction operation consisting of cleaning a designated area of trees, timber, brush, other vegetation, and rubbish; removing surface boulders and other material embedded in the ground; and disposing of all material cleared.

Clearing, grubbing, and stripping are different in every climatic zone because each has different types of forests and vegetation. The nature of a forest can be determined from records of the principal climatic factors, including precipitation, humidity, temperature, sunlight, and the direction of prevailing winds. The types of forests can be generally classified as temperate, rain, monsoon, or dry, according to the climates in which they exist.

Clearing usually consists of pushing uprooted trees, stumps, and brush in both directions from the center of the area to be cleared. Clear so that you place debris, also known as spoil material, in a designated spot with only one handling. In clearing landing strips, for example, it is generally necessary to dispose of material along each side of the strip outside the construction site. If the site permits burning, you can reduce the haul distance by piling brush, stumps, and trees on the site and burning them. Production in this field must be estimated, rather than calculated.

Grubbing is uprooting and removing roots and stumps. In grubbing, burn or blast stumps that are difficult or impossible to pull out, even with winches. Your supervisor will decide the method. If the stumps are to be removed by blasting, call upon a qualified blaster to do the job. If they are to be burned, you may be assigned the task. Green stumps require continuous application of heat before they catch fire. Check with your supervisor about safety measures to keep the fire from getting out of control if you have to do any stump burning. Remember, it may take as long as three or four days for a stump to burn out. Keep a check on the burning during this period. If a project has a high priority and time must be saved, you will probably blast stumps, rather than burn them. After removing stumps, fill the holes and level the area to prevent the accumulation of water.

Stripping is removing and disposing of objectionable topsoil and sod. It may either follow or be done with clearing and grubbing. Actual earthmoving begins with stripping; surface soil and rocks are removed from the area to be excavated. Deeply embedded rocks and large boulders may have to be blasted before they can be removed.

The material removed by stripping is called spoil. Unless otherwise directed, dump spoil along the area to be excavated within range of the earthmoving equipment. If the spoil will not be put to some use like turfing or finishing the shoulder of a road or runway, waste it along the edges of the project, as shown in Figure 6. Take care not to disturb necessary drainage.

Equipment commonly used in stripping consists of a dozer, a scraper, and a grader. As mentioned earlier, the dozer is the most often used when removing trees. Dozers can handle all short-haul excavations up to 300 feet. For long-haul excavations over 300 feet, use scrapers. You may also use a scraper on fine soils for shallow stripping. Use a grader mainly for shaping and finishing a stripped surface. It is adaptable also for ditching, side casting, and sloping banks.

Drainage is the construction of facilities needed to allow excess surface and subsurface water to flow from the construction site. Properly designed and constructed drainage systems are one of the most important parts of a construction project. Without proper drainage, rainwater and water running off the surrounding ground could turn the area into a lake. It is also necessary to drain off surface water that would soak down and wet the subgrade.

The elements determining drainage needs for a road or project site are the amount of annual rainfall in the area and the routes or areas that can be used to collect or channel excess surface and subsurface water. These areas include lakes, ponds, streams, or voids such as gullies.

The type of soil is critical to the design and construction of a road. It is poor judgment to construct a road over or through clay, sand, or other undesirable material if it cannot be properly compacted. Bypassing this type of material is best.

If a road surface is to endure continued use for years, it must have firm support from the subgrade. Remove all organic materials, such as living or decayed vegetation, from the area of the subgrade unless the road is for emergencies or is temporary, such as a detour or military road. In designing and building a road, consider the type of drainage, the type of soil, and the amount of clearing or grubbing necessary.

To facilitate drainage, excavate diversion ditches to conduct all surface water into natural channels or outfall ditches. Construct outfall ditches to drain low or boggy spots. At the point or the end of the system where the accumulated runoff discharges into the disposal point, the runoff is technically known as discharge. The discharge point in the system is called the outfall. This preliminary drainage work is done at the same time the area is cleared and grubbed.

The finished drainage system usually consists of ground slopes, ditches, culverts, gutters, storm drains, and underground water drains. Use open channels to intercept or control surface water. These should be dug by bulldozers, scrapers, backhoes, or motor graders, depending on the circumstances. Construct culverts to drain water across a construction site. Subdrains to drain groundwater are usually excavated with ditchers or backhoes. The drains used are French drains, which are perforated or open-joint tile pipes. Figure 7 shows typical covered and French drains.

Remove runoff water from rain or melted snow from the area by constructing an adequate transverse slope or crown. This runoff collects in ditches and drains into the nearest natural drainage channel. Drainage for construction sites can be provided by building the ends of the site sloping towards the middle or sloping from one end to the other. These types of drainage construction are shown on the runways in Figure 8.