What I laughingly called a driveway for twenty-plus years of living
here was basically just an area of dirt next to the house, which stayed
bare enough to park and even do car maintenance on but still grew enough
grass and weeds that I had to mow it. The surface was quite firm
and for the most part it was perfectly adequate, but even with the good
drainage around here some of it would basically turn into a mud bog
in every March snow-melt and I almost got the car stuck a couple of times.
Throwing down a little more gravel didn't do much. And the recent
road paving job
had left me with sort of a klunky interface to the street and questionable
water-runoff management. But now that they were done with all that it
made sense to think harder about a better driveway and a more integrated
connection with the new asphalt out front.
But I didn't want to just go with a generic asphalt job for my own piece, where I'd have to be worried about pitch, runoff, and frost heaving. Water-permeable systems with good drainage underneath are basically immune to frost issues, as the water doesn't become trapped enough to push upward. I stopped by the local Planning department to ask about permitting and any impermeable-surface limitations, which they don't really care about as long as it's not too close to wetlands, and when I floated the idea of a permeable system they were like "well, then you'd be totally all set". A little research found that I could have a system of nice flat paving blocks with permeable joints in between, but *not* the kind with big holes through the middle that grass grows up through. I wanted something that would act like an asphalt driveway but still drain water straight through itself.
This idea had been in the back of my mind for a while, and in fact I still had flyers from a couple of companies I'd run into at the local home-shows a couple of years ago. I measured out a sensible perimeter to get an idea of square footage and started making some inquiries, and after a little discussion decided that it was worth going ahead with. This would be an integrated system built with a sensible water-handling structure underneath, not just a few bricks stuck into the ground. My shopping-around wasn't really all that far-ranging, because the fellow from Premier Pavers I happened to chat with explained it all way better than anyone else I tried to contact. Some time later we put pen to paper and scheduled it up.
This is how it went, in four parts. Page navigation is at the bottom. Click any thumbnail for the larger picture with more detail, and use your "back" button to return.
|The "before" shot, on the morning the project started.|
|The project manager arrived in the morning to confirm the paperwork and mark out the boundary of the job. He drove some stakes near the corners and ran some string between them to set up the lines.|
|The strings served as a guide for spray-painting the boundary on the grass, using that ubiquitous orange construction marking paint that I'd seen so much of in use this year. For the piece extending closer to the house, we had decided that a gentle S-curve would be most compatible with turning a car through that area so he just roughed that in by hand.|
|Next was to "shoot" some final-grade heights, using a laser level and its companion beeper-on-a-stick. We had two non-negotiable height reference benchmarks: the high side of the street intersection, and the concrete slab in front of my side stoop diagonally opposite. Everything else was derived from those. I also wanted to try and make most of the middle field as level as possible, thinking ahead to where I'd be working on cars and such.|
An initial take on the final grade was marked on the stakes and the
string moved to that level. The string was in part to indicate the
limit of excavation, which would generally end six inches outboard
of the intended driveway boundary itself.
We actually decided to lower that far back corner a couple of inches, as the land slopes off fairly quickly there and we agreed that full dead-level height all the way out would make a huge "shelf" that would have to be backfilled. So we sort of split the difference.
In the meantime, a couple of guys arrived from the subcontractor slated to
do most of the excavation work to get a look at the job before arriving
They seemed sort of undecided about being able to do it, as their truck was
in for repairs and they weren't sure when they'd have it back. The PM said
he could just skip to one of the other four or so subs they normally bring
in, and left the decision up to them.
That was all that happened in the morning, but other things were also in the works behind the scenes as far as materials procurement. That's one of the parts of a job like this that the client doesn't really see, unless it's in the form of a project manager wandering around a jobsite on the phone to suppliers most of the day.
|And sure enough, a huge flatbed rig wormed its way into the neighborhood that afternoon to deliver the pavers themselves. I wasn't sure why these were brought in first as plenty of other stuff would have to be used beforehand, but here they were and we already knew where to stash them out of the way.|
|It was sort of funny to see the load straps flying off by invisible hand, like flat yellow snakes, as the driver on the other side released the ends and flung them over.|
|He has a dead-simple but clever aid to spooling up the straps onto the ratchets -- a cordless drill with the long end of a hex wrench clamped in the chuck. Since there's a hole in the end and the sides of the ratchet reel fitting, he just cocks the bent end into there and lets 'er rip with the drill in the "unscrew" direction.|
|Then he dropped the forklift off the back, and picked up the "grabber" attachment on the forks.|
It works like ice tongs, the more lifting force applied the tighter it
grips the object. The side rails have hard rubber faces for plenty of
friction onto stone type material. It works in sort of a click-on /
click-off way, e.g. drop the pickup point to open and a stop keeps the
pantograph from closing for the next lift, drop one more time to release
the catch and swap over to lifting mode. This mechanism was a little
flakey and he had to bang it down a couple of times to get it to
With the side pressure it looked like the bottom layer was about to explode downward, but it was all held by steel strapping.
|Here's the ingenious little part, which allowed placing the bundles out beyond the string line without actually having to roll out that far: little extender feet that drop down just beyond the wheels. This change in fulcrum allowed the body of the forklift to counterbalance the considerable weight of the paver bundle as the entire fork assembly slid forward over the wheels.|
|Bundle placement continued, and I realized that there would be just enough space for them as the forklift sort of got in its own way and couldn't place them too close together, and the guy didn't seem to want to stack them up the allowable two-high. Maybe that risks gouging them up more?|
|To get to the second half he had to move the whole truck to the other side of the street, because the forklift couldn't reach all the way across the flatbed. In all, ten bundles got dropped around the periphery of the worksite, conveniently distributing them close to where the installation would happen.|
|And this is what we got. More details can be found on the company's webpage about them, and later on I found their in-depth technical info which describes theory and maintenance.|
|Speaking of random bricks stuck in the ground, I already had some. The remains of a brick walkway were mostly buried in the dirt leading toward the stoop, and I wanted to save those when the excavation happened. We had a note about this on the paperwork so they wouldn't get disposed of as part of the fill, but later that afternoon I decided to just uproot them all and stash them aside my own way.|
The excavation crew arrived in the morning. I already knew it wouldn't be the same guys who had stopped by before, from email the PM had sent the previous evening, so I ran them through my same small bit of intro information about stuff like expected soil composition, surface pitches we were aiming for, fill recovery caveats, where the bathroom is, etc. This actually wasn't easy because this crew was all Brazilian, and only the head guy understood enough English to discuss things in any detail. But it soon became clear that this was a tight-knit group well used to working together, with its internal communications in rapid-fire Portuguese.
Okay, I thought, this was going to be interesting. On one hand it wouldn't really allow me to ask that many questions, and on the other hand it wouldn't allow me to ask that many questions. That made sense, didn't it? What it really meant was that I'd have to come up with more of my own guesswork about what they were doing and why.
|First thing off the trailer was "the machine", a Bobcat equivalent that would do most of the work. Then came a big roll of geotextile and a bunch of tools. While this wasn't a bobcat from the official Bobcat company, I'm going to just generically refer to it as the bobcat like the rest of the industry does anyway. Think kleenex, xerox, thermos, etc.|
|The bobcat backed out again toward the street but ... Oops! Lost something?|
No, it wheeled around to pick up its fork attachment, which could then
lift the *cutest* little roller out of the back of the dump truck. Clever
transportation hack. It looked a little dicey driving the roller onto
the forks under its own power, but it worked.
This wouldn't necessarily work with just any dump truck; this one had a dual-hinge tailgate with locking pins to allow opening in the appropriate direction or even complete removal, to use it as sort of a walled flatbed.
Soon after, with the bucket safely clipped back on, ground was
ZOMG, here we go!
|The dirt area had at some point long in the past been a gravel driveway, using fairly rounded stone that seemed to average about 1.5 inch size. Very much like the same "river pebbles" type that I was using for various drainage projects. So while its surface had silted in over the years it was still heavily laced with those, and I wanted to save a little bit of that to have on hand -- either as a source for more of that type of stone if I wanted to sieve it out, or just generic fill. But I didn't want the bobcat driving over the septic and the moss toward the back where I was aiming to store the pile.|
|I grabbed one of their wheelbarrows and had him load me up with some top-layer scrapings, and huffed it out back to make a nice little out-of-the-way heap. Heavy stuff! I only wanted two or three loads, so I was done with this in about ten minutes and got out of the way. They were totally cool with this, although I think they might have been hoping I had someplace to dump *all* the fill. Eep.|
|Nope ... the rest of that volume would have to be hauled away, as agreed. Their dump truck was pretty small, and didn't take long to fill up. The other guys climbed up to help level the load as it formed and they went as high as they could, but soon had to roll the wind cover over it and take off for the dump site.|
|Excavation could continue while the truck was off-site, and the driver worked more of the hole and just piled the dirt up temporarily in another part of it.|
|While the guys driving the bobcat were capable of artistic exactness, the actual edge at the orange spraypaint got sliced open by hand to make sure it was accurately shaped.|
|I made sure to stress protecting the roots of the big pines along the side as best as possible, i.e. not just ripping up or cutting any large structural ones. They were on board with this, understanding that pine trees are the first ones to go over in the Big Storm, and were clearly pushing the bobcat very carefully while working along that edge. But to make a cleaner cut, a few of the small roots we found just got neatly sliced off. We only found one significantly large one, and it was out near the end where the bottom grade could rise to just over it anyway.|
|Loads continued to fill and go out, albeit fairly slowly. Evidently the site they found that would accept the fill was fairly far away, and it took quite a while for the truck to return each time. There was some bit of hurry-up-and-wait going on around this, but the guys remaining on site kept fairly busy anyway. They all knew what needed to be done and just worked toward whatever they could in the meantime.|
|The hole was starting to look vaguely squared off, with a uniform depth.|
|And look at this wonderful dirt! We were down to the same lovely high-percolation sandy soil that so favored the street upgrade and the related work out there, and it was looking like the entire bottom of the pit and beyond was this stuff. This would yield great infiltration capacity.|
|A typical cross-section could be seen here: about six inches of darker more organic topsoil on top, and then the sandy subsoil. It was also about now that I realized that slab at the bottom of the stoop was quite a bit thicker than I thought. Glad it was remaining in place.|
|As digging neared the street, tossed-up dirt had made it completely unclear where the asphalt ended and more importantly, where that little water-shedding berm sat. To make it more visible to the guy in the bobcat, I took a shovel and carefully slotted a line all the way across to show him where the limit should be.|
He didn't plant the bucket right on that line, but while coming close was
using sort of a back-and-forth technique with the bucket tilted sharply
down to make a more angular cut. He'd push down a little and then drag
backwards, rather than pushing the dirt up which would risk taking the
asphalt with it.
Asphalt really isn't very strong stuff.
|Upon reaching the berm itself, it was back to good ol' hand pick work.|
|After a while, the entire pit was open with only a minor pile of dirt left to still go out. Wow. I now had a big squared-off hole in the ground.|
A first short run of filter fabric was laid across by the street.
|Because the next thing to show up was a load of mixed aggregate, which would form the foundation structure around the new driveway's edge. Part of that would remain right here under where it got dumped.|
|Now they stretched out more thin pieces of geotextile, and started loading the aggregate onto it.|
|The bobcat brute-forced its way across the pile to make a little ramp for itself, to load the remaining fill dirt out, and the truck was sent off for the last dump run. Next thing was to distribute the aggregate onto the filter-fabric layer taking shape all around the edge.|
|One of the guys asked me about a water supply, and I realized that I hadn't thought of that at all but obviously they were eventually going to need one -- they'd brought a cement mixer, after all! So I set up a hose from downstairs and ran it out front through my special little pass-through tube [shown here near the middle]. With that they began wetting down the aggregate, to make it pack better. They had formed it into a well-defined shape, which would effectively serve as a solid footing.|
|The aggregate was then compacted down with this funny little plate vibrator. This isn't like the big road rollers, its frequency is actually quite a bit higher -- maybe 50 or 60 hertz, but definitely does the job.|
|The wetting and vibrating left the aggregate *very* hard. Well, they do make rural road surfaces out of this stuff, so no real surprise there. The magic component is probably the fine stone dust that's in it, allowing very high packing density. It's not concrete, but has similar broad-area compressive strength.|
|After a first compaction run around, a second layer was dropped on and spread.|
|The border of aggregate was leveled and compacted all the way around. This formed what's called the "bond beam", a firm containment for the rest of the drainage structure to come. Meanwhile the bobcat was making final grading tweaks to the bottom of the pit.|
Because the dirt in the bottom had gotten fairly chewed up and was thus
no longer "undisturbed earth", they rolled it nice and flat. I'm not
sure if this would have lost it any infiltration capacity, given the
type of soil it is, but it's just part of the standard prep.
The Unilock technical guide talks about this some, but dwells more on stability than permeability. It also talks about "proctor density" and the moisture content vs. compactibility of aggregates, which helps explain the hosing-down.
|So for a while it was a whole lot of sprayin', rollin', and shakin' all going on at once. A total festival of playing in the dirt.|
|Which left the whole perimeter structure ready for the next step, conveniently at the end of the workday. Some of the aggregate was left as a more gentle ramp at the street end, to facilitate driving down.|
Which they used to store most of their stuff in the space overnight,
since they'd be right back again the next morning.
None of the neighbors commented on this, but I was ready to respond with "hey, ya like my new dump truck?"
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