My commute now days takes me along most of a 10 mile stretch of highway that was largely obliterated by tropical storm Irene a few years ago. They rebuilt the portions that were completely gone (taken by a river...pavement, sub base, guard rails...everything gone...looked like it must have in 1750. At any rate, this year they are completely resurfacing the entire length to the tune of $1 million/mile--close to $12 million in all.
After they ground the upper 4 inches off and hauled it away for reprocessing, they brought in enormous "roto-tillers" with 4' diameter grinding toothed cylinders and rototilled the remaining pavement and sub base material down nearly two feet. Then they rough graded and vibrator rolled it, followed by a "cut and fill" team consisting of another two graders, and two more rollers.
I talked to the project manager the other day about the equipment they were using. It looked like all Topcon; brand new...they had at least one, if not two base stations set up near the areas that they were staking out and grading. The finish graders and one rollers each had what I guess are called "rovers", as did the guys staking out.
I stopped and asked about the accuracy; he said that as soon as he turns his on and gets a lock (took about 30 seconds when I was there), he checked and said he was good to a tenth in elevation and 3 tenths horizontal, but that it gets better the longer it's on.
He had the entire length of the highway in his data collector, and it showed him exactly how high the base for the forthcoming asphalt should be. He said the entire operation: the graders, the rollers, the stake out guys' rovers etc. could all be observed in real time back at the trailer. Haven't been there yet to check it out, but will soon.
Is this "RTK"? "Differential GPS"? They the same thing? Other than my commute now being nearly entirely on a dirt road all summer, it's very cool to see this work.
All hail Trimble, All hail Trimble.
Thats the way its going. google intelligent compaction. Thats what your seeing on the roller. Theyre not just eliminating the stakes, the testing will be gone soon as well. Mark my words operators will be next.
That is generally known as "machine control". RTK is a part of it. Surface modelling is another.
To add to that, they are also using what topcon calls their "millimeter system" which uses a rotating laser combined with gps to guide the grader. It uses the laser for vertical and the gps for horizontal position. It would amaze you how tight it will grade. For really accurate work Trimble has a robotic system that a robotic total station tracks a target on the grader. The gps guided machines are usually +/-.05' when measured properly, and that is "close enough" for most of the work we are doing in my neck of the woods. It is like anything else in the tool box though, there has to be lots of quality control being performed at all times. Sadly, it has ruined much of this generation of equipment operators.....
We tried out the millimeter GPS a couple of weeks ago on a milling machine and an asphalt paver on some roadwork. When it works, it works well. However, we spent the better part of a week trying to get it to be consistent, and never did. The first thing they always tell you about is the airports they have used them on. We are in West Ky, and there are very few roads here that have that kind of clear areas to set up the lasers where you can get much use out of them. The theory is good, the logistics are not. The limiting factor was the 15' maximum height difference between the lasers and the receivers on the equipment. Those on the equipment are already mounted 12-13 ft. high to clear traffic, people and trucks. We were testing it on a 24' wide road that was on a 15' fill, so the only place to set the lasers was on the shoulder, which appeared to be too close to work with. Had control points every 250', 4 lasers, but still had trouble with consistency. Might check good for awhile, then switch lasers and be off. Another limitation was that the lasers had to be set on a control point. We've got a 3 mile road project with variable depth overlay, that will have traffic running on one side or the other the whole time. Would take an enormous amount of control.
Going to be trying the Trimble robotic system soon. It's more expensive, but I'm thinking the logistics of where you can set the robots will work better.
The Trimble UTS system is good, I am a Trimble man all they way, but it too has quirks. The actual setup of the robot and connection is easy, keeping the machine calibrated and cutting right is another issue. We have 22 machines currently outfitted with dual mast GPS and 19 base/rover setups. We grade large light industrial sites, warehouse type sites with buildings in the million square foot range, and 95% of the time with plenty of checks and adjustments we do all our finish work including grading base stone with GPS.
I'm with the machine control crowd here. It took me a couple projects to convince me, but it does seem to work.
Just need the RLS to set control, and then verify things as the project moves on. Likely sign off on something at the end. No problem and it beats bending over to pound hubs. But it is the RLS's control, so that is key.
No different than setting a hub for a curb or MH with some cuts on it. I'm not so sure I'd want to be creating 3D files for MC guys though, but I will set the control. Pass the baton downhill and let the PE deal with it..... :-S
Our county purchased a BOMAG reclaimer a few years ago. That is the overgrown rototiller thingamabob you mentioned. It is impressive to watch in action. They will chew through dirt, asphalt and concrete. Warning: they do not chew through cast iron objects, such as manhole lids. They are tough but they are not indestructible.
The county has used theirs in several ways. One is to tear out sections of unpaved roads that are crushed rock over dirt to allow recompacting to smooth out serious potholes. Another way it is used is to make multiple passes of several inches in depth to completely break up old chip and seal roadbeds for proper recompaction and a couple layers of new chip and seal. One use this year has been to mill an inch or so off old chip and seal roads prior to applying a new coat to smooth out ruts and such caused by heavy wheel traffic over time.
I believe the one they have cost upwards of $300,000.
Yeah, you don't want to be too close downwind of one of those babies in action. The fumes and dust are enough to choke a horse . . . or cow. 😉
Sophisticated Elevation Notification System
In addition to the Topcon Hiper GA system used to sculpt the highway, I noticed they're using these Hi-tech natural light, optically reflective, celulosic Centerline-to-shoulder gradient advisement panels.
Can you buy these at a surveyor's supply outfit?:-D
"...Gradient Advisement System..."
Love it!
I'm going to start calling my stakes that.
(Reminds me of the straws I pick up at Starbucks to blow the drill dust out of lead and tag holes in concrete: "air channelizers". Makes 'em tax deductible.)
