Good compaction of fill is essential if you are to avoid subsidence. The Romans and Egyptians knew it and so did the so-called “primitive” tribes of Great Britain. While the ethos remains the same, the equipment used to achieve it has evolved considerably. By Richard Campbell
While feet, oxen and sheep used to provide compressive force on earth fill areas, like so many other pieces of earthmoving equipment, the modern compactor owes its invention to Robert G. LeTourneau.
LeTourneau produced his first compactor, a towed sheepsfoot type, in 1928. It was built, as were so many other of his inventions, to overcome a problem he had encountered on an earthmoving job. Stunningly simple in design, LeTourneau called it a sheepsfoot roller after the design and shape of its feet. Fabricated from two welded steel drums with rows of peg-like projections, the item was quite heavy and performed the task it was invented for admirably. Extra weight could be added to increase the compactive effort.
LeTourneau realized he was onto a very good idea and investigated other types of foot designs to cope with varying types of soils.
Most significant of the new designs was the “wedgefoot” compactor which, along with its weight and the shape of its feet, asserted a kneading action on the soil, packing it in tightly.
Also, the wedgefoot was more effective than the sheepsfoot in breaking up clumps of earth and small rocks.
Other equipment manufacturers were not slow in picking up on LeTourneau’s idea and soon there was a great proliferation of compactors, offered by an even longer list of manufacturers. These compactors were all tractor-drawn, had few moving parts, and were very ruggedly constructed. Requiring practically no maintenance they could be towed behind almost any tractor that had sufficient horsepower and flotation to pull them. Because of their simplicity, examples of sheepsfoot, wedgefoot and grid-type compactors from this early era can still be found in daily use today, many, many decades after they were first sold
Manufacturers of these early compactors included all the major ancillary equipment companies of the 1930s and 1940s such as LaPlant-Choate, Bucyrus-Erie, Garwood, Baker, Isaacson, Vickers-Onions, Hyster, Allied, Ateco, Southwest, Carco, Wooldridge and of course, LeTourneau.
It wasn’t until the late 1950s with the increase in size and scope of earthmoving projects that self-propelled compactors first appeared. One of the pioneers in this field was Hyster, of Portland, Oregon who fabricated and fitted both wedgefoot and sheepsfoot compaction drums to “war-weary” motor scraper tractors in place of their drive tyres. Particularly popular machines used as compactors were early Caterpillar DW20s and Euclid FDTs which leant themselves to this kind of conversion readily, and Hyster correspondingly sold a lot of conversion kits to customers who needed to speed up and modernize their compaction operations.
Another company to see the potential of scraper tractors as compaction units was the Rome Plow Corporation who fabricated a series of sheepsfoot discs which could be fitted in place of the scraper bowl on job-weary motor scraper tractor units thereby turning the machine into a self- propelled compactor. Rome called this invention the “Roman Wheel” and they sold quite a few units, especially in the south western United States where large earthmoving projects abounded.
As for purpose-built self-propelled compactors, the debate is still out on who actually introduced the first production self-propelled compactor. LeTourneau had been experimenting with its diesel-electric ‘Power Packer’ series machines since 1959 when the first prototypes made an appearance. These were very large compactors intended for big projects but the machines were complex, expensive to fix, and sales were correspondingly low.
Another manufacturer who offered a true self-propelled compactor early on was Rex-Pactor.
Introduced in 1963, and of an unusual tricycle wheel design, the original Rex 3-30 had a GM/Allison powertrain and weighed around 16 tons. Utilizing an open ring design on its wedge-shaped feet, the machine compacted from the bottom up and was very manoeuvrable.
The operator sat sideways so he could keep an eye on comings and goings in the fill and steered the machine hydraulically with a simple tiller control.
The machine was also fitted with a hydraulically controlled dozer blade so the operator could maintain the fill and drift material into low spots if necessary. As an added bonus, the blade could also be used to assist machines that had become stuck on the fill. This simple addition started a trend as a blade is now a commonplace implement on self-propelled compactors.
The compactor had come of age!
As was the case with the towed compactor, very soon other companies were offering their own versions of a self-propelled compactor and by the mid-1970s, most of the larger manufacturers had one or two in their catalogues.
Some of the more notable candidates included Bomag, who offered quite a range of machines, Ray-Go, (who eventually became part of Caterpillar), Dynapac, FWD-Wagner, Komatsu, (whose first effort, the WF22A was a bit of a disaster), Hyster, who offered a 22 ton monster called the C-455A and of course, Caterpillar.
Caterpillar was a late starter into the self-propelled compaction field but eventually ended up dominating it.
Caterpillar’s first compactor was a conversion of it’s 824B wheel dozer, which was itself a modification of the 988A wheel loader.
This proved to be successful design and several other models were soon introduced starting with the smaller 815 (17 tons) and the larger 835 (35 tons), both introduced in 1970.
All of the Cat compactors have wedgefoot wheels and have matured over the years into excellent compaction machines.
Far removed from the towed compaction rollers of the 1930s, the self-propelled compactor of today is a sophisticated and specialised piece of equipment, designed to quickly bring fills to strict compaction requirements. It should be noted at this point, that during the evolution of the self-propelled compactor a further, even more specialised machine was born – the trash compactor.
Unfortunately, these machines fall outside the scope of this article.
The New Zealand connection.
New Zealand contractors were not slow in recognising the benefits of good compaction and were using products imported from the UK and USA, plus many items sourced from US armed forces war surplus by the end of 1945.
Along with these imports, several enterprising New Zealand companies began manufacturing their own versions of towed sheepsfoot and wedgefoot compactors. Hewco, Pacific, Moore and CWF Hamilton have all produced home-grown compaction equipment worthy of note. These compactors can still be found around the country putting in a useful day’s work.
In addition, New Zealand’s isolation and “number 8 wire” ingenuity has also produced some other interesting compaction pieces, some based on crawler tractors! These are indeed rare and precious gems if you ever run across one!
For the model collector
Although the compactor is a specialized piece of earthmoving equipment, many model manufacturers do have examples of compactors in their ranges, mostly to 1:50 scale. These are generally readily available and the author recommends both DHS Diecast and Buffalo Road Models as a source for these should you require one for your ‘spread’.