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. |
Day 1
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. |
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
for real.
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. |
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. |
Then he dropped the forklift off the back, and picked up the "grabber" attachment on the forks. |
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. |
Day 2
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. |
The bobcat backed out again toward the street but ... Oops! Lost something? |
Soon after, with the bucket safely clipped back on, ground was
officially broken.
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. |
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. |
The hole was starting to look vaguely squared off, with a uniform depth. |
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.
Why there? |
Now they stretched out more thin pieces of geotextile, and started loading the aggregate onto it. |
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. |
After a first compaction run around, a second layer was dropped on and spread. |
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. |
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