Road improvement project 3

Things went quiet for a few days, but behind the scenes various resources were being lined up and schedules filled in. A roadwork operation takes good coordination between several different entities. [Thumbnail pictures are linked to larger ones.]

The low point of the road may not have had great drainage before, but the old drywell must have been doing something because now with it gone and the new structures sealed over with plates and relatively impermeable soil, the road wasn't draining at all. Modest amounts of rain had created a long-lived mud pit. The local grade had changed a little anyway since more material had been placed back over the infiltration pits than used to be there before. That minor factoid became important later on.

The crew figured to get a little head start on the regrading needed near the entrance to the new subdivision. The original road profile went over a fairly large hump just before the intersection, which needed to be cut down about 18 inches to make the required design grade and the turn into the entrance beyond a little more level. First, the fairly hard upper surface was loosened up with a little excavator work.

The bobcat operator went at further cutting and shifting of dirt with much enthusiasm! Apparently this is the only way to get a nice deep dig with a small skid-steer loader, especially when the packed soil was still giving him a bit of a fight.

They continued working the hump for a while, pushing most of the material down-slope to level the downhill side of the intersection as well. That's why this process is called "cut and fill"...

If I crouched down quite low, I could see where the laser level reference plane was peeking out from behind some of the interim piles of dirt. This was about the only time I was able to catch the laser spot in a picture, as it rotates past pretty quickly.

A brief attempt was made to bring some of the dirt over and fill in the muddy area a little, but this was soon decided to not be worthwhile as main grading was about to fix all that anyway.

A fairly severe cut into the closest abutter's front lawn was needed, but fortunately it already had a retaining wall of railroad ties so they didn't have to re-engineer a slope.

A survey crew from the engineering company arrived to re-establish the exact road boundary limits, which had been done several months before but only in a rough way and many of the old marker stakes were already missing. This was a more thorough run to lay out the exact lines for the revised plan. As I half-heard them talking on the radio I realized that they were working with very fine position differences that the transit was able to distinguish at hundreds of feet away, such as the guy at the reference marker saying "move 2 inches to your left and 3 towards me".

They were using a Nikon/Trimble DTM-521, an instrument referred to as a "total station" that not only shoots distances and angles at something better than 3 seconds of arc resolution, but does most of the math needed right on board to determine linear distances between arbitrary points where the reflector pole is moved to. I couldn't find a manual for this specific model but this one for the DTM-502 is very similar and describes how they work. Two known reference points were enough to determine all the rest of the ones they needed.

The guy doing the walking had the pole with the corner-reflector on top and a bundle of stakes to drive in, and they mapped several accurate positions up each side of the road to establish the lines. Each stake was then painted bright orange and labeled "2 feet off edge of pavement", indicating the absolute limits of work. It was fortunate that the official boundary would just miss a line of fence whose chances of survival had been in question for a while, as well as my own line of little trees out front.

They were done with all this on the early side, so I went out for some errands after they'd wrapped up for the day. As I returned back into the neighborhood I spotted a little nest of unusual heavy equipment quietly resting in a side pull-off along the road. And there was the fearsome Pulverizer they'd been talking about! An odd-looking beast indeed, and apparently named the "Recyclesaurus". It was clear that all hell was about to break loose on the street the next morning.

    Return to dirt

The next day began cool and crisp, and crews started arriving. Soon I could see the Pulverizer arrive at the top of the street where it was going to begin doing its thing. Half the street already had existing pavement that was only a few years old, but it had been decided to newly pave the entire run rather than just the dirt stretch. So it all had to get redone.

They wasted no time getting started, as this piece of equipment is in high demand for other jobs around the area. The machine is a Wirtgen WR2500-S referred to as a soil stabilizer, but there's little technical difference between "cold recycling" of bituminous paving or other top-layer material and making sure the soil base underneath is of a known uniform consistency. The mechanism is the same. These machines and the surrounding methodology are becoming much more mainstream in modern repaving operations, as they are fast and generate no waste. The picture here links to a short video; click to download or play it. There's a better and longer HD video here of the same type of machine running, that someone in some western-US locale took during high-altitude mountain road work.

This is the guts of the monster: a big powerful drum festooned with lots of carbide-tipped teeth. This drops down into the old pavement and about four inches beyond, scraping up a mix of everything. That's basically all there is to it -- the material gets broken up and mixed in one clean operation as it passes over the top of the drum. One key is that the drum spins fairly fast, throwing material vigorously all over the place inside the shroud around it. Take a moment to consider the power that's going on under here... The guy driving it paused to raise the covers and crawl under to check the drum every so often, which was when I could grab this picture. He said that he does lose a tooth tip or two here and there and has to check after every two or three passes, and has boxes with plenty of spares to bolt on.

This is what the reclaimer leaves behind, decorated along the edges with the tracks of its monster tires. It's all so fluffed up it sits quite a bit higher than the original surface, but that's all the product consists of -- exactly what was there before, sort of aerated and thoroughly mixed into a fine aggregate. No need to truck any old pavement away and recycle it elsewhere, which is one of the major benefits of this process. And the machine is surprisingly quiet while doing all this, considering that it's ripping up eight or more inches of hard bitumen and dirt and whatever else is there.

The output is very soft, and would obviously need to get rolled down again to form the new substrate layer.

The first pass reached the end of the paved part, turning a little less than half the roadway width back into uniform dirt. It took all of about fifteen minutes. Right about then the grader zipped [relatively] around it and entered the picture to start working on the dirt part of the road.

The recycler raised up to lift the drum chamber clear of everything, and headed down to the subdivision intersection to turn around. It steers from both ends, giving it a fairly tight turning radius despite its size. While it looks "bigger than a house" in this shot it isn't, quite, but some of Wirtgen's large-scale mining machines definitely can be.

The grader could now start merging some of the recycler output into the rest of the dirt stretch, building a more uniform slope from the hill down toward the engineered lowest point.

In the process of prepping the edge of the roadway for the recycler, other equipment had torn up a bunch of poison ivy growing along the side. Hopefully nobody got it on themselves, either directly or by, say, touching the dump of the bobcat later while it still had the urushiol oils on it. Nasty stuff, I thought maybe should have walked up here and nailed it with Round-Up years ago but it's not on my land.

A little preliminary roller compaction was done on the loose stuff, but there would be much more of this later on. Even after that, the recycled part was still sitting above the original surface.

Hang up and roll ...

The second recycler pass established the other edge of the roadbed, leaving just a narrow strip in the middle.

Which was taken care of and blended right in on the third and final pass. After this the Recyclesaurus drove its ponderous bulk out through the subdivision to get loaded onto the flatbed to take it away to the next job. [It hadn't come in that way because that crew didn't know about the special temporary construction-equipment entrance off the nearby highway.]

A new end of original pavement was established at the top of the hill and around the bend a little, as a neat ridge which got bermed up just enough to let cars go over it. This was taken a little later after everything got post-treated.

Now the grader could attack the whole roadway, and started working all the material back and forth, up and down, to gradually mold the new shape of the roadbed according to the plans. It's another one of the types with the leaning front wheels. In an idle moment the driver explained that it's a really useful feature to not only counter the thrust of the plow, but give much better stability and tracking when one whole side of the machine is rolling in a roadside ditch.

The grader is quite the piece of engineering. This box sitting up on the main arm, looking like something off a NASA project, connects out to a bunch of sensors on all the motion axes of the machine and enables full computer control of everything it does. Instead of trying to explain it to me on the ground, the driver had me stand on top of the blade and raised me right up to cab level, so he could show me the display and control instrumentation [no pix but they're actually not that exciting]. It not only shows exactly where the blade is, it can accept some amount of programming, such as "go from depth X to depth Y at this camber over the next 200 feet". Optional modules can also automatically follow a laser level, allowing almost entirely hands-off grading. It's kind of funny how the crew guys get pretty friendly when you start asking good questions about their gear.

The roadbed level at the lowest point next to the catch basins needed to be way down in the hole at the tiny bit of orange tape on the stake [blue arrow]. The grader driver made an honest try to dig in and get there, but stopped for a re-think when strange stuff started appearing under the blade. It was a little too low, and getting too far into the infiltration area.

As a result, some of the filter cloth got ripped up and exposed the drainage stone. Not good; the grade would need to leave substantially more dirt over all this.

As the grader tried to work this a little more, an additional headache appeared in the form of more old pavement, buried under the dirt area, that nobody had any idea was there!

At one point a long piece of this cracked loose and slid right along some old railroad ties that used to be the edge of the lawn here. Evidently more of the road used to be paved but over the years became covered up with the dirt/gravel aggregate that the town brought in more of each spring to resurface the roadbed.

So the guys were like "okay, now what do we do with this". The reclaiming machine was long gone by then, so having it recycle more of the roadbed wasn't an option.

Answer: break up the pavement some more, fling the chunks out into the middle of the roadbed and go over it with the "meat tenderizer" attachment on the grader. This is the old-school way of reclaiming asphalt, albeit not as elegant as the cold-recycling method.

Grading passes had reached the top of the infiltration structures; concrete and the little lifting cables were seeing the light of day again. Something needed to be done to cover this back up, because they couldn't pave right over it let alone install anything else on top.

Almost inexplicably, part of the answer was to *remove* some excess material from the whole area. Recall that a little too much dirt had gotten put back over the infiltration pits in the first place, and that was somehow throwing off the whole operation of getting a proper gradual slope down to the catch-basin area. The grader left a ridge of extra dirt in the middle, for the loader to come along and grab. Eight or nine bucket-loads went away into the subdivision to get dumped onto the big piles of spare fill back there.

The loader operator took an idle moment for a photo-op. Same enthusiastic guy featured prominently throughout all these pages, who does everything and never stops! He was even on the site some weekend days taking care of tasks needed to try and meet schedules.

The amount of total material in the roadbed seemed about right now, and the grader kept working it back and forth, up and down, and got the area over the drainage straightened out while working closer to a good overall rough grade for the whole stretch. As the operator put it, "I'll bat it around a little more." I was wondering how he was finally going to get rid of the ridge in the middle as it looked like he just kept pushing the same dirt back and forth, but eventually it spread out and disappeared.

Despite the minor setbacks, a workable basic grade was established toward the end of the day and the path that water would take toward the catch basins wasn't compromised.

    Shakin' all over

Then came the part that had me terrified. A lot of vibratory compaction had been done on the subdivision roadbeds some months before, which rattled the crap out of all the abutters' houses even at some distance away. Code requires this to stabilize any disturbed base soil under paving so they had to do some quantity of it, but I was concerned enough about what might happen when it was right in front of our houses that I filed an official letter with the town hall Planning staff and even escrowed a batch of "before" pictures with them from all around my foundation as proof of pre-existing conditions should it become necessary.

I read up on the subject a bit. I asked about any possibility of seismic monitoring during this procedure, as suggested by this damage guide for homeowners. As opposed to the short impulses from blasting and pile-driving, continuously vibrating rollers at certain frequencies can set up resonances inside structures that amplify the motion effects. Lower frequencies are generally worse than higher ones even at the same peak particle velocities, which is why "slow" events like earthquakes cause more damage. No plans for monitoring were about to happen, but the head of the town Public Works department tried to assure me that vibratory compaction for roadwork is done all the time in residential neighborhoods and while it might feel pretty annoying to nearby residents and make loose items walk around a little, he's never heard of it causing actual structural damage.

So roll they did, and I shot one of the closer passes from inside the house just to see if a recording could capture the effect. The picture here links to the video; click to download or play. Bass response on a point-n-shoot camera microphone can't come close to doing it justice, of course, but a few things can be heard rattling along with. The periodic metallic scraping is from the roller itself, possibly contacting its own plow attachment a little as it goes around. For all my apprehensions, however, the vibration didn't seem all that bad this time.

The key thing to note here is what happens when the roller comes to a stop. The vibration is done by a spinning eccentric weight inside the roller, which has to ramp up and down to its normal running speed and stops when the roller itself stops. It's during those brief transitions that the frequency becomes much lower and the shaking effect is *much* more profound. I was hoping that all the rolling passes would begin and end farther away from where I was, and here the guy just stopped in the middle of everything, backed up a little, and then just sat there. WTF??

It turned out that the machine had simply throttled itself down and wouldn't move or vibrate any more, because the throttle control solenoid on the engine had failed somehow. Throttle controls on something like this are sort of an on/off thing, not really about fine control but just a fixed setting that keeps the running RPM high enough for the required output. Apparently this is common and has happened before, so they reached in and bypassed the throttle linkage with a bungee cord and kept on working.

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