824’s versus 825’s. “Method Spec” compaction theories. “Let the scrapers and the water pulls take care of it.” I’ve seen a lot of mass grading contractors take different views on compaction when building big fills.
Personally, I don’t trust anything but a sheepsfoot or a vibratory compactor to compact a fill.
I have no respect for rubber tired dozers as compaction machines. RTD’s are made for cleaning up load-out floors in mines and pushing slobbers into the crusher that the haul trucks leave behind. I don’t believe in them on scraper projects. Some may argue that if you fill the tires with calcium chloride they work great. I disagree.
To clarify with some of the Californians; 95% of the material I’ve seen in California is so evenly graded in it’s composition that thin lifts underneath rubber tires will work. But that’s a very isolated situation; I’ve not seen many other places like California.
Any material that an RTD can sufficiently compact, a sheepsfoot can do as well, if not better in most cases.
There are far too many horror stories of contractors who built big fills, only to have them settle 3-5 years later due to improper compaction techniques. I don’t want to tarnish my reputation like that.
Wolper Construction is one contractor that branched into the mass grading sector a few years ago, did some residential work involving some big fills, and then got kicked/walked off the project (depends on who’s side of the story you hear). A different contractor came in and finished.
Five years after completion, some people backyards slipped away from their $1 million+ house and slid down slopes, houses settling and basements cracking, roads falling apart and numerous utilities problems. A little core drilling and some material sampling later showed a lot of problems in the bottoms of the fills: all because of the corners cut in the compaction department (and some very poor choices regarding fill material). Last I heard the lawsuit filed against them for the problems in their fills was $10 million.
This is only one of many horror stories I’ve heard about compaction failures, often due to improper equipment utilized during construction.
A lot of times, it is the general contractors/developer’s fault for not policing the contractor. But I still don’t think it’s excusable for any contractor to cut a corner like that just because there was no dirt cop out there checking compaction.
Many residential projects will have no inspectors monitoring the big cuts/fills. No nuclear moisture/density tests taken until you’re into the AB grades in the streets. Too many contractors cut corners and take advantage of this to cut the cost of a compaction machine working full time. Or at most, put an RTD on the fill because it’s a cheap machine.
As you get into projects like transportation/railroad you start seeing an inspector monitoring the fills and testing randomly. Specifications that have to be met and adhered to, etc. Overall, a lot better level of quality control. In most transportation projects, DOT’s won’t approve RTD’s as compaction machines. They used to, but its becoming rarer and rarer every year. They greatly prefer to see a sheepsfoot or some type of vibratory compactor building their roads.
I’ve done some refinery site development projects where the 657’s were required to lay down 8” lifts (measured by a GPS), compacted with a sheepsfoot compactor, and pass 95%+ compaction throughout the entire fill, up to 20’ in some cases. Not hard to achieve with an 825, but I’d love to see an 824 do it.
I’ve also seen some projects where 94% and lower would fail you, and 100% would fail you. Try achieving that with an RTD. A lot of times you don’t need a vibratory compactor as in many materials a sheepsfoot will accomplish that.
Articulating soil compactors/sheepsfoot’s are a lot more expensive to purchase and maintain than RTD’s, but I think it’s a justified expense that a lot of contractors cut the corner on. I’d rather make up for the extra expense of a sheepsfoot somewhere else on the project, versus reducing the cost, using an RTD, and risking a compaction failure.
The other big change being seen is the utilization of GPS on compactors. Nothing beats a skilled operator in an 825H with a GPS. I’ve seen some very good operators in 815’s, 825’s and 835’s that can finish large pads to +/- .1’ with no assistance from a grader or paddlewheel if the machine is equipped with a GPS.
Having the sheepsfoot on the fill finish the grade to spec beats the hell out of having a blade and paddlewheel follow the scrapers and balance all the pads to finish grade.
I always laugh when I see companies putting GPS systems on 824’s or 834’s. Those machines are not very good at maintaining grades compared to a sheepsfoot and can’t push nearly as much material.
I’ve seen several good sheepsfoot hands that can get their machines onto fill slopes and maintain slope grades quite well. Anything less than a 3:1 is pretty manageable for a sheepsfoot to maintain as long as the fill is relatively small/narrow (roads, railroad grades). Excellent operators can get onto 2:1 slopes and keep them graded to within spec.
Larger pad fills will require a dozer on those slopes to maintain the grade of the fill slope while the compactor focuses on the lift compaction.
I’ve been on some shot rock jobs where the fill dozers working the slopes can’t make the slope look decent until the sheepsfoot walks the entire slope to break up any larger rocks, pack them into the slope so that the dozer has some fines to work with to take the slope to finish grade.
Overall, I think any company that does mass grading projects, is far better suited to have a good sheepsfoot compactor (preferably with GPS) to build all fills, regardless of type of material. They’re more versatile, and in the long run are a lower cost alternative to those damned RTD’s.
