Saturday, September 17, 2011
So, where did I leave off? Ah, that's right, Pile Driving!
As mentioned before, this house was built on top of old, unstable fill. And there is an old stream below this area, which means there is the potential for peat. During the purchase, I had a geo-tech bore test holes and from that determined that there was no peat to be found (good!), but the soil was fairly unstable in the upper layers. This means that I would need to either use a *LARGE* shallow footing foundation, a slab foundation, or pile piles with a grade beam.
With either the shallow footing or the slab, I would need to excavate to soil that would compact and in my case, I knew that wasn't likely. So that would mean over-excavating and then bringing in fill and compacting it. That sounded like a massive and unknown pain in the ass, so I chose to go with pin piles. This would have the potential to be more expensive, but it would also mean a fixed installation schedule and I wouldn't have to worry about the underlying soil, I could just dig and be done with it.
And bonus, if you use 2" pin piles in Seattle, testing is not required, so the homeowner can install them! And you all know how much I like doing this kind of stuff. So again, here is a picture of my pipe that I'll be using. It's 2" schedule 80 galvanized pipe. I didn't have to use galvanized, but it will last *a lot* longer than black and it wasn't that much more expensive, so, what the hell. All told I ended up buying 80 10ft lengths. Unloading these was a pain in the ass as they each weighed about 50lbs.
I bought the pipe from a pile driving contractor who also sells the supplies for "self-installs". So when I placed the order, I also ordered couplers and caps. When I picked up the order, I realised that I could easily fabricate the couplers and caps and save a shit ton of cash.
Specifically, they wanted $25 per coupler. A coupler was just a piece of schedule 80 1.5" and schedule 80 2" pipe welded together.
I realised the material cost for each coupler was less then $5, and the same thing for the caps (which were slightly less at $20 per unit). And to put this into perspective, I would need at least 48 couplers and more likely 60+ and 48 caps.
So I could earn about $2k in sweat equity fabricating them myself. And bonus, I like to weld!
Here is an example of the couplers I made.
Here, you can see the piles I've started on the outside of the house. In total, I would be driving 40 piles from the exterior and another 8 from the interior of the home.
When I started, I rented a 90lb jackhammer from Aurora Rents with a special pile driving bit. In total the hammer with bit weighed somewhere over 110lbs or so. So imagine balancing a jackhammer on top of a pipe, 10ft off the ground and trying to keep it all going straight, while not falling off a ladder.
In addition, the goddamn pipe would mushroom in the tip and I would need to beat the pipe with a sledge to get it out of the tip before I could drive the next pipe segment.
Suffice to say, I don't have any pictures of these escapades, but it was foolhardy at best, and *REALLY* f'n slow. It took me roughly 8 hours to install the first 2 piles. Admittedly I was slightly defeated, until I picked myself up and started calling around questions and I found something that made me believe in man / machine love.
THIS IS IT! The tool of my dreams. It is a 140lb pile driver. It's entire job is to sit on a pipe and beat it into the ground, without me needing to balance it.
I could only find one for rent in King County, and I ended up renting it for an entire month for $900 and it was worth every penny. EVERY PENNY.
This tool saved my sanity and gave me hope.
Remember how I told you it was 140lbs? Well it's almost entirely cast iron, and it's a bitch to lift. Even as burly as I am, I knew I couldn't keep lifting it all of the time, especially when I am running 10ft segments of pipe. So I fabricated a tall stand with a chain winch. This allowed me to easily lift the pile-driver to the top of the pipe without killing myself.
Remember how I said the homeowner can handle the install of 2" piles? Well the catch is that the city requires someone to inspect the pile installation and ensure that they are driven to the geo-tech's refusal criteria. This means I had the privilege of paying a guy to watch me install the piles and make sure that they moved less than 1" in 1 minute for 3 consecutive minutes.
And now, a video of the pile driver in action!
Posted by Jeremiah at 5:17 PM