As those of you that have been reading this blog probably know by now, I like to know how things work. This leads me to ask a lot of questions, and yesterday Tony (the site superintendent) and I got to talking about helical piles. Naturally, I found myself asking "So, what are helical piles?" To answer my question, we took a field trip outside and into the area enclosed by the construction fence (an area I normally avoid due to the heavy machinery and, well, mud). And that is where I learned (and now you get to learn, too!) all about how the house is being supported during construction.
You see, since the house is being extended out in two directions, holes had to be dug adjacent to the existing structure for the basement areas that are being added. In the center of the first picture, you can see the very bottom of the french doors that lead out of the library onto what used to be a patio. Obviously, that is where the ground used to meet the house. The "trench" or hole they dug (where the ladder is going) extends down to the bottom of the basement and the actual foundation of the house. The dirt that used to be there before they dug the trench is really important, since the ground is a large part of what was holding the house up and in place. Removing it leaves the house vulnerable, and so supports had to be added to hold up the house before pouring the foundation for the new addition.
Enter helical piles. Helical piles are giant augers (sort of like screws) that are drilled into the ground next to the foundation. In the picture to the left (a close up of the same area as the first picture), the two pipes coming out of the ground are the tops of the helical piles.
A metal "clamp" is then attached to the top of the pipes. The third picture (left) shows a close-up of the clamp (that's not the technical term for it, but I don't know how else to describe it). The clamp has a flat metal piece that extends out from the pipe and under the base of the foundation. This forms what looks like a little shelf that the foundation sits on, which provides extra support from underneath the concrete.
The helical piles are regularly spaced along the foundation to provide even support. On the wall in the pictures (the library wall), there are about four helical piles. I didn't get close enough to see how many run along the dining room, but I'm guessing about 6, based on the length of the wall. This same system can be used to repair homes in which the foundations have settled or cracked because, once the supports are under the foundation, they can adjust the tension and thus move the house up or down (kind of like a car jack).
Here's a picture of our helical piles from another angle. (For the curious reader, the dark metal "cage" surrounding the shiny silver helical pile is installed prior to pouring the concrete footings, which they poured late Friday afternoon.)
If you're interested, there are some better pictures of a similar system at this site: http://www.piertech.com/residential/solutions.htm
I love these updates. What will the net gain be once the renovations are finished? More bedrooms? New chapter room? Can you post some of the architectural renderings of how it will look?
ReplyDeleteAmy, awesome questions, which are probably running through the minds of several readers. Not to delay the fun, but let me get this info together in a regular post so its more accessible. I'll also see if I can scan some drawings (but I'll have to see if I have any of a scan-able size).
ReplyDeleteOkay, quick answer: eight new bedrooms (bumping capacity up to 85-90), new dorm-style bathrooms in the basement (like the ones upstairs), new large chapter room, and remodeled kitchenette. Because more students will be living in the house: more computer room space, larger dining room (room for the whole chapter!), expanded cold dorm, second laundry room. New paint and carpet throughout the house. New roof. Fire sprinkler system (YAY!) in new and old (DG requirement, and just plain good idea for safety).