STRIPPING

Stripping consists of 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, you should dump spoil along the area to be excavated within range of the earthmoving equipment. If the spoil will not be put to use, such as turfing or finishing the shoulder of a road or runway, it should be wasted along the edges of the project, as shown in figure 15-64. 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), scrapers should be used. A scraper may be used also on fine soils for shallow stripping. A grader is used mainly for shaping and finishing a stripped surface. It is adaptable also for ditching, for sidecasting, and for sloping banks.

DRAINAGE

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, such as lakes, ponds, streams, or voids (i.e., 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. It is best to bypass this type of material.

If a road surface is to endure continued use for years, it must have firm support from the subgrade. All organic materials, such as living or decayed vegetation, should be removed from the area of the subgrade unless the road is for emergencies or is temporary (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. Outfall ditches are constructed to drain low or boggy spots. At the point or the end of the system when 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 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. Open channels should

Figure15-64.-Stripping. 15-40

be used to intercept or control surface water. These should be dug by bulldozers, scrapers, backhoes, or motor graders, depending on circumstances. Culverts are constructed to drain water across a construction site. Subdrains to drain groundwater are usually excavated with ditchers or backhoes. The drains used are french drains (perforated or open-joint tile pipes). Figure 15-65 shows typical covered and french drains.

Runoff water from rain or melted snow is removed from the area by constructing an adequate transverse slope or crown. This runoff is collected in ditches and drained 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 15-66.

Figure 15-65.-Typical sections of covered and french drains.

Figure 15-66.-Longitudinal drainage of runways. ,-