There are a number of methods to control the final finish of a road surface by using motor grader. No matter which method issued the motor grader will set the Moldboard to the trimming tilt and at 45°. With this tilt the cutting edge is almost vertical to the road surface and only scrapes the surface. It is also advisable to use new cutting edges or reasonably flat surfaced edges. By lightly moving over the surface the material is trimmed from the high sections and deposited into the lower sections. The motor grader should start at one edge and move to the other side of the road using several passes. A roller should follow the motor grader to compact the surface and care should be taken not to let the surface become dry.
Methods of Control.
If the final road surface level is not required to be accurate but the finish surface is to be smooth, as in maintenance work, then this straight edges method is suitable.A profile board can be constructed for this purpose. This board is constructed to have a 3 percent difference from one end to another and is generally about 2 meters in length. The board is used with a spirit level to find the cross fall and without a spirit level to see any variations in flatness along the length off the road. This board can be easily carried in a Site Engineer’s vehicle for spot-checking.
This method is acceptable for most classes of roads and has the advantage of being very quick when working with the motor grader. It however requires a surveyor or technician to do the initial setting out. Once the setting out has been done it should not have to be done again other than to replace damaged pegs. Two wooden pegs of say 1 to 1.5 meters are securely placed outside the shoulder edge on both sides of the road. A nail is then driven into the side of each peg at reduced level that has been calculated to give a height 300mm above and parallel to the designed finish road surface. A string line is strung between the upper and lower nails, for straights and between the two nails for curves. The Site Engineer/Site Supervisor then reads a tape measure vertically down from the string line and informs the motor grader operator as to the depths of cut or fill required.
This is a very accurate method of control but is very time consuming. So it is not used extensively any more. After the material has been placed and compacted, the surveyor or technician hammers small wooden pegs into the surface at the correct reduced level. The motor grader operator then trims to the tops of the pegs. This method requires a laborer to clean the top of the peg after every pass of the motor grader in order that the operator can see the peg. Pegs can also be knocked out and have to be replaced. As the material is already compacted the pegs are very difficult to hammer in to place.
This is only used in highly specialized areas such as Freeways leveling and not in general use. This method would include Laser leveling etc. The manufacturer’s methods would have to be followed and the Motor Grader fitted with the special controls.