If the roads are to be paved with gold, you want to get it right the first time. The sub-base and base also must be prepared with utmost precision.
Fortunately, the roads are not paved with gold, as turn-of-last-century immigrants metaphorically imagined. Yet, with some of the high-value material being placed on roads, highways, parking lots and airport runways it may seem that way.
Site-prep contractors today are feeling the squeeze in terms of tighter deadlines, higher quality results and skinnier budgets. Sounds depressing enough to want to drive a motor grader off a steep cliff . . . but the problem is that very often the cliff is what needs to be graded.
Ready to run
Laser augmentation for GPS-based 3-D grade control systems has been developed as another option for achieving very precise, vertical grade for jobs with tight tolerances. Contractors today have the option of using a robotic total station 3-D system or adding laser augmentation to their GPS-based system.
Using laser augmentation can increase vertical accuracy to 0.01 to 0.02 ft (3 to 6 mm), which should satisfy even the most stringent finish grading requirements. By comparison, those using GPS-only systems see their accuracy at 0.1 ft (20 mm to 30 mm). Clearly with the sub-base and base being more precise it allows for the more accurate placement of the overlay.
So, how does laser augmentation work? The system requires a laser transmitter, which is a standard rotating laser typically set up on a tripod. The best systems do not require the placement of the laser transmitter on a known design-plan mark but allow the transmitter to essentially define itself as the benchmark base. The setup for a flat laser plane is that simple.
Once set up, the system is configured to be aware of the orientation of the laser plane. It is then possible to receive laser-augmented grade on the system. Then, horizontal positioning can be received from the GPS grade control system, and high-quality elevation control is achieved through the laser-augmented grade system.
The world is not flat
Unfortunately, not all jobsites are flat. The site may be hilly. To optimize the laser-augmentation system, a sloping laser plane needs to be set by tilting the tripod-mounted laser transmitter to properly orient it. It is critical to define the orientation in order to benchmark the system.
A critical technical issue is to make certain the laser plane is precisely aligned and benched or grading errors will occur because of the incorrect orientation. There are some grade lasers available that include both a grade-match mode and automatic axis alignment to make setup for single- and dual-slope grade work easy.
The receiver is typically mounted on or integrated into the machine’s mast. Some systems make the machine operator’s task easy by enabling the laser setup from the operator compartment. Additionally, the operator can select the position of the transmitters using “cross hairs” selection from the plan view.
Great for the grader
Laser augmentation offers its greatest use on motor graders, although there are contractors who use it exclusively on dozers and some are finding advantages when it is used on excavators.
In the race to save time without compromising quality, laser augmentation for GPS 3-D machine control is certainly a significant player. Time is saved because contractors can perform both rough and finish grading using one machine. Additionally, there are the safety and time-saving advantages of operating in a stakeless environment.
It is quite simple: Once the bulk grading is completed, the contractor can set up and orient the laser transmitter and use the same machine for complex final grading—good as gold.
