Bulldozing

Bulldozing (drifting) is the process of pushing materials straight ahead in front of the dozer blade. Bulldozing is most efficient when the blade pushes as much material as possible, as shown in figure 11-25. The maximum working distance for dozer production depends on the speed and blade capacity of the dozer. However, the maximum working distance is usually 200 to 500 feet with 300 feet being normal for a medium-size dozer.

To maximize the amount of material pushed, push downhill whenever possible. With the assistance of gravity, a bulldozer can push a far greater load downhill than on a level grade. When you are dozing down a steep hill, a separate full-length pass with each load is unnecessary; instead, push and pile several loads at the brink of the hill and push them all to the bottom in a single pass.

Figure 11-25.-Bulldozing.

Figure 11-26.-Side-by-side dozing.

Figure 11-27.-Slot dozing.

Side-by-side dozing (fig. 11-26) and slot dozing (fig. 11-27) maximize the amount of earth drifted by reducing or preventing spillage around the outer edges of the blade.

SIDE-BY-SIDE DOZING.- In side-by-side dozing, two dozers work abreast with blade edges as close together as possible, preventing spillage around one blade edge on each dozer. Side-by-side dozing requires time-consuming maneuvering of the dozers; therefore, it is impractical for hauls of less than 50 feet and more than 300 feet.

SLOT DOZING.- Slot dozing is done by first building a pair of windrows with the spillage of several passes. As shown in figure 11-27, the windrows serve as barriers to prevent spillage around the dozer blade ends. Under favorable conditions, slot dozing can increase production up to 50 percent.

Figure 11-28.-Spreading.

Figure 11-29.-Culvert backfilling.

SPREADING.- Dozers are ideal for spreading fill material brought in by haul units (fig, 11-28). Position the blade in a straight position, so the material is drifted directly under the cutting edge.

BACKFILLING.- Backfilling is the process of replacing excavated earth, as shown in figure 11-29. When a culvert is backfilled, the dozer should not cross the culvert unless there is at least 12 inches of compacted material on top of the culvert. If a bulldozer is used to bacfill a culvert, the best method is to make diagonal passes over the material, ending each pass with a swing that brings the blade in line with the culvert.

The angle blade is preferred for bacfilling a trench, because material can be side cast into the trench while maintaining a steady forward motion, as shown in figure 11-30.

Figure 11-30.Trench backfilling.

When a pipe trench is bacfilled, fine material is placed around the pipe and coarse material above it, so the pipe is supported by well-compacted material. However, covering the pipe to full depth in short lengths may concentrate weight and break pipe joints; therefore, cover the pipe in successive layers, rather than all at once.

NOTE: Be careful in pipe trench bacfilling to avoid dropping large rocks directly on the pipe.

FINISHING.- Whether clearing or spreading material on a roadbed, no job is completed until it has been smoothed and drainage is established. This is called finishing and should be done at the end of each Shift.

Blade the job lightly with about a half of a blade of dirt. This fills in any low spots or holes. Leave a windrow on the side that you are working toward. At the start of the next pass, cover half the blade width. Continue in this fashion over the project or section of the project you have worked that day before you shut down for the day. Finishing the project in this manner supports drainage and prevents having to walk over piles of dirt or through mudholes.