2004-5 Pipe

2004 12 22

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So, this week we ran into our first complication.

Some of you may already know that 50-60 years ago there was an artificial pond on our property, formed by a concrete dam. This dam is now buried and runs under the front deck of the house and is under a bit of the front (river side) of the house itself. An enormous amount of concrete rubble and "engineered fill" went into the pond before the first house on the property was built, and the same happened again when the current house (ours) was built 9-10 years ago.

When the existing 24" concrete pipe was put in along Charmian Road it was cut through the top 6-7 feet of this dam.

I knew about this and the engineer and contractor were made aware of the existence of the dam. What we were not aware of was the size of the dam.

This week we found out. It's 15-16 feet tall, about 18-20 in thick at the top, and perhaps 6-7-8 feet thick at the bottom. It's big.

The new 60" concrete pipe has to go through this dam considerably lower in the ground than the existing 24" inch pipe. This was known at the outset, and a "time and materials" contingency clause was put in the bid to cover concrete cutting.

That's where we are now. Concrete cutting will commence Monday. You might be wondering how you cut concrete that is several feet thick. It's done with what looks like a very thick (1/4 to 3/8 in.) piece of wire that has industrial diamond coated beads on it spaced about 3 in. apart. A hole is drilled though the concrete, the wire is threaded through, and then threaded onto a series of what look like pulleys that maintain the tension in the wire as it is forced sideways through the concrete. It will take 2-3 days to make either 2 or 3 cuts in the dam, and then the free piece will be knocked over and hammered apart. It's not being hammered apart in place to keep the vibration from being transmitted into our house or the neighbors. I have learned that concrete weighs about 150 lbs per cubic foot, and that about 300 square feet of cutting can be done with one of these wires before it's used up. All of the rubble will be "lost" in the trench for the new pipe.

(I am including this link simply because it mentions the "Mega Demo" at the "World of Concrete" convention, both of which are superb names. I'd love to go to the "World of Concrete" convention.)

Here are a couple of snaps of the pipe that has been laid so far, and the dam.

First, a snap of the old pipe headwall, the new pipe (no headwall yet) and the temporary black plastic pipe used to keep the water out of the way.

The face of the dam. What looks like a crack about an inch up from the bottom of the photo is the bottom of the dam.

The top of the dam.

I can hardly resist saying "Dam. This is fun."

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