 For the most part, betuminous pavement failures are pretty easy to recognize. And in many cases, the corrective action is pretty simple too. For example, this situation can be taken care of with a pothole repair. And sealing the cracks here will add years of life to the pavement. But this situation is a great deal more complicated. As you can see, a portion of the pavement has settled below the surrounding roadway. That alone tells us that the activity called for here is base repair. In this program, we'll take a look at how these situations are best corrected. Keep in mind that the most important part of the corrective action is to eliminate the cause of the failure. In some cases, removing and replacing some of the base material may be enough to solve the problem. Other times, a drain may have to be installed to channel water away from the road. In any case, the cause of the failure has to be corrected, if the repair is to last. Basically, base repair involves first determining how much of the damaged pavement should be removed. Then, excavating completely through the pavement to the base course. The next step is to determine the cause of the failure and the appropriate solution. After the corrective action is made, one to two inch material is placed and compacted. Followed by a bituminous mix, placed and compacted in six inch lifts. OK, those are the basics. Now let's go through each step of the procedure in detail. As with any other maintenance activity, the first step is to set up all the proper traffic control devices. Because of the size of the grader, you'll always have to close at least one lane. So you'll need a lane drop symbol sign if two or more lanes will remain open to traffic. Or a one lane road ahead sign if traffic will have to alternate through the work area. And of course, cones are needed for all lane closures. OK, the next step is to determine how much of the pavement should be removed. By marking the area, the grader operator will have better reference points for the limits of excavation. And you'll be able to determine if you have enough of the proper type of material on hand. During excavation, be careful not to undercut the remaining pavement. The sides of the repair area should be as vertical as possible. Also, take care not to disturb any of the material under the pavement. During this phase of the operation, only the damaged roadway should be removed. That's because the next step is to determine what corrective action should be taken. And the less you disturb the underlying material, the better you can see what caused the problem. In this case, an underground spring has eroded away the base material. So the best corrective action here is to install an underground drain. Causes of base failure include such things as plugged culverts, proper drainage along shoulders, cracks in the pavement, or anything else that inhibits the flow of water away from the road. As you can see, water is the primary cause of base failure. So in many cases, the solution is to repair something along the road rather than under it. With that in mind, let's go back to the repair. Because the damage here is caused by underground water, a drain has to be constructed to keep the water away from the road. The major things to keep in mind are first, to extend the drain completely through the shoulder. And second, to give the drain a slope of at least an inch per foot. Once excavation is complete, backfilling can begin. Be sure to use a minimum of one to two inch material like this so the water can drain easily. This material should also be used to replace any sub-base material that had to be removed. After backfilling, be sure to compact the material. Remember, this will be the foundation of the new pavement. It's equally important to compact the material in the drain. Settlement in the shoulder has to be avoided too. Now the base material can be placed and compacted. In many cases, you can reuse the material that was excavated. Just be sure that it's dry and free from soft or spongy substances like clay. You'll almost always have some hand work to do during this step. Because this too is part of the foundation, be sure the thickness of the lift is uniform throughout the area. And be especially careful not to overfill the repair. The new base material should be only as thick as the original base. That way, you can maintain the support as well as the pavement thickness. As with the sub-base, the base material should also be compacted as much as possible. Now, before the pavement is reconstructed, apply a thin coating of tack material for a few inches along the existing pavement and to the sides and bottom of the repair area. This procedure will help bond the new pavement to the existing pavement. In order to get the most compaction for the new pavement, you'll normally have to place it in two lifts. The foreman's handbook says that no lift should exceed six inches. So, if the reconstructed pavement will be about eight inches thick, place two four-inch lifts. Here again, the thickness of each lift has to be uniform and compacted as much as possible. The top lift, however, has to be fine-graded first. Pay special attention to all the transition areas. The new pavement has to match the existing pavement all around. You'll find that it's a good idea to compact the material after each grading pass. That way, you can better determine how smooth the transitions are. After fine-grading, the steel wheel roller can be used. This, of course, provides the final compaction, but it also smooths the transitions as much as possible. And that's it for the pavement. But because a drain was constructed here, the shoulder also has to be fine-graded and compacted. During this step, the two most important things to keep in mind are that the slope of the shoulder has to allow for drainage and the edge of the shoulder has to be flush with the pavement. Remember, one of the major purposes of base repair is to eliminate the cause of the failure. And here's the completed job, a reconstructed pavement over a firm foundation that provides for proper drainage. Try to keep the points you've seen here in mind. And remember, if you can't find the cause of the problem under the pavement, examine the surroundings. Anything that inhibits proper drainage is likely to be the cause.