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|Log Skidder with roller|
Road maintenance requires the usage of some type of compaction. We've all heard of 'steam rollers' and seen various rollers around. Actually steam rollers have gone the way of steam shovels. Gone! there was a time when these machines had steam engines on them, but that time is long gone. There are actually quite a few types of rollers and the one seen here is not all that common.
Many rollers are self propelled, implying that they drive around under their own power. The roller seen here is NOT of that type. It is a towed roller that is pulled along like a trailer. Of the towed rollers the most common in the Pacific Northwest is the "Hyster Grid Roller", probably because Hyster was in the good old days, a Portland, Oregon company. The Grid roller was similar in appearance to this, but instead of being 'smooth bore' the roller part was a 'grid' of about 4 inch mesh. The unit was then weighted with concrete weights on both ends and typically pulled with a Cat.
The roller shown here is of Italian manufacture and is much more 'hi-tech' than a grid roller in that it is a vibrating roller. It has approximately a 100 HP air cooled Deutz diesel engine (German made) which turns an out of balance shaft in the center of the roller. The main frame of the roller is vibration isolated from the roller via some concealed 7.50 x 16 pickup tires which connect the roller to the roller frame. When running you can feel the ground shake for 50 feet or more away and the manufacturer says that it is effective in compaction up to 15 feet deep.
This is not the kind of a roller you might use to roll down asphalt, but when applied to a pit rock road it does a good job of setting the rocks and bashing down the high ones effectively smoothing up the road. It is also very effective in getting rid of the 'tire busters' that show up on a pit rock road. On a hard surface road it will break up even the hardest of the basalt rocks or smash them into the road surface. We like to put it over our roads in the spring while the roads are still a little soft. At that time the road will still be flexible and have a moisture content suitable for compaction and the road can sort of be 'set for the summer'. Likewise, a well compacted road is very resistant to taking water implying that it will hold up much better the following winter. By using this technique, we can generally avoid applying crushed gravel to the road which increases the roads costs considerably since you have to get crushed rock from a rock crusher site which is further away and more expensive both in freight and in cost since it has been processed.
Popularly called 'steam rollers', there is actually a variety of compaction equipment on the market. Towed rollers are not all that common any more. Most are self propelled, and not by steam. The trash compactor will likely have the general appearance of a large front end loader (usually with a blade instead of a bucket and will have iron wheels instead of rubber tires which do the compaction. A common type of compactor for doing subbase compaction is a single drum roller with a 2 tired unit with an engine articulated on the other end. this provides driving tires to propel the machine around and a drum to do the compaction. They get around a little better than a double drum roller which is often used in asphalt compaction, but their ability to navigate is still limited. The only real advantage of the towed roller is that you can hook it behind a dozer or what ever (we use a large log skidder) and go compacting places that the fair weather compactors won't go. You will also see rubber tired compactors used on Asphalt, but they like the double drum ones clearly are not for loggers.
The next difference in the compactors is the drum type. The smooth drum is a necessity for asphalt, but is not necessarily the best for subgrade and logging road compaction. Alternatives include a sheep's foot roller and a pad foot roller. The sheep's foot roller has essentially spikes on the roller. The idea here is that spikes will stick into the ground and compact at some depth, but at the same time stir up the surface. A pad foot roller uses short rounded protrusions on the roller which provide added pressure (over a smooth roller), but because they are rounded, they don't agitate the surface like a sheep's foot.
The question of when to compact is a tricky one. Part depends on what you are trying to accomplish. Compacting soil is like making snowballs. If the material is too wet or too dry nothing happens. The science of road compaction involves determined the optimum moisture content and applying the compaction at that time. If the material is too dry you will be looking for a water truck, and if it is too wet you will be out plowing it on sunny days trying to boil off some of the water. On a pit rock road, however, a logger may go about the matter differently. A favorite time for the roller is when it is entirely too wet to compact properly. The reason for this is that when you are trying to do is to push the big rocks down and emulsify the ground a bit to create a surface which is even and in filled between the rocks with native soil. This makes the relatively smooth even surface. Then you get off the road and stay off of it until it dries to a compaction optimum, and return and compact it. Using this two stage compaction method you can create a usable driving surface out of fairly large rock.