Site Control - Principle 1
1. If at all possible, hire the engineering firm that designed the project to place your site control.
Your earth moving project site was surveyed and designed by the engineer on a virtual grid, really no different than the graphing paper you used back in school. Quantum's modelers take the engineer's plans and create a 3D model for your grading equipment that is referenced to the virtual grid originally laid out by the design engineer's surveyor. Site control is what allows your GPS equipment to know where you are on the engineer's design and places your machine control model in the correct place both horizontally and vertically. This leads us to our first principle of good site control.
Why hire the design Engineer's surveyor, you ask? There may be someone that will do it cheaper, faster or you want to help out your brother-in-law's new surveying business. All of those are great reasons to hire someone else, but not good enough. The engineering firm that designed the site is the only one that has all of the information necessary to set your site control and the authority to figure out how to fix it if there is a bust.
If getting it right the first time is not a good enough reason here are a few more (the list continues to grow) real world examples, courtesy of our clients to help you understand how important correctly placed site control is.
On one of his first GPS jobs Contractor A took the low bid from a surveyor to place site control. He completed rough grading and excavated trench foundations, which were poured…only to find out his site control, and all of his work, was rotated 2.8 degrees from the correct orientation….. The design engineer's surveyor immediately found the issue as soon as he set up onsite.
Contractor B thought he would save a buck and just use the control he found on one of the plan sheets - referenced to a couple manhole centers and a fire hydrant. What he missed was that vertical control was based on a railroad spike in an electric pole. When the design engineers surveyor staked the building it was 0.2' low. The elevations numbers on the manholes and hydrant were from old city plans. The $800 bucks Contractor B saved by setting his own control did not pan out He had to haul in thousands in rock to raise buildings and parking lots 0.2'.
Contractor C worked on a large residential project that was in state plane control - or it seemed to be. Turns out the job had switched engineers a couple times. The original firm set up their site control and design in a "modified" state plane system. Somehow they started off a couple feet from true state plane control but went ahead and used that setup for design. The low bid surveyor hired to place the contractor's site control put it in the true state plane system. When Contractor C set up on site the machine control file and existing roads were not quite matching up. Contractor C lost 2 weeks of production by the time they figured out the issue and hired the design engineer to place control.
Contractor's D through Z tried to use single point control on their engineered projects….. No need to share the stories here. It just never works right.
Contractor's A, B and C would have avoided costly delays and unplanned material expense had they chosen to hire the design engineer's surveyor. In every case the design and machine control model were correct and in the right location.
Principle 1: If at all possible, hire the engineering firm that designed the project to place your site control.