Pebble Hill Observatory

[jimt]

See if a magnet will stick to any of those "pebbles". You know just in case. I can't help it. Watched too many episodes of meteorite men.

Jim

[Galileo3269]

My goodness, meteorites that big would probably pay for that observator he,s building plus some......

Steve

[Joe Timmerman]

DSCN3902.jpgAfter the holes were dug, we dragged our frame back over the holes and cribbed it up to the proper elevation. We used a transit to make sure the frame was level. The tops of the sonotubes will be attached to the top of the frame on Sunday. We also made sure everything was square. As I mentioned before the frame was designed to have two sides of each sonotube supported at the correct height and exactly where my 4 x 5 support posts will be centered.

One nice thing about the sonotube frame was everything was screwed together. When dismantled all lumber will be reused in the construction of the observatory. Little to no waste.

So far so good. It was time to BBQ steaks and drink beer.

[ChuckWalters]

Looks great so far! A nice big open field to view from. Steaks? Be right over!

[Joe Timmerman]

DSCN3910.jpgDSCN3908.jpgFull disclosure - This post describes events that happened over a month ago. I did not want to begin posting this thread until I actually felt there was a chance I would be successful in this project. As you will see, there were some real challenges

The next day (May 20, 2012) we woke up to clouds and the threat of rain. Since I only had Troy for the weekend, we decided to proceed with attaching the sonotubes to the frame, getting them vertical, putting some gravel at the bottom of the tubes, and backfilling the tubes.

We immediately discovered that some of the holes needed to be expanded. Occasionally while we were digging with the skid steer, the auger would hit a large enough rock to shift the auger over. To keep our holes in the proper place, we had to hand dig out the rock and expand the holes so the tubes would be vertical and in the proper position. It was quite a job.

While doing this work, it started to mist. We kept working. Then it started to gently rain. We kept going at a little faster pace. Then it started to POUR, and the site turned into a mess. We finished as best we could setting the tubes and pouring 4 inches of gravel in the bottom and around the base of each tube.

That night it rained 3 inches. The next morning to tubes were flimsy and soaked. The site (because of heavy soil) was a disaster. There was no way I could pour cement. Troy left Monday morning (May 21) and all I could do was wait for things to dry out.

[Joe Timmerman]

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After two sunny days, things begin to dry out. I haul a trailer load of sand from the local sand and gravel pit and use it to mix with my soil to backfill the rest of the tubes. Amazingly the sonotubes survive the heavy rains and I feel confident they will hold up ok. We mix and fill all 16 tubes in about 4 hours.

The pictures show the tube layout for the observatory, attached garden shed, and the gantry. I went with 8 inch tubes only after my local architect assured me they would carry the load. They are buried almost 4 feet deep and sit on about 4 inches of gravel. They stick out of the ground from 8" to 16" due to the slope of the ground.

[ChuckWalters]

Glad you had some good weather to dry things out. Your OBS is going to be big! Looking forward to watching this be built.

[Joe Timmerman]

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Disaster strikes. It had been a very wet spring and our ground was saturated. My wife's rain garden was full of water and local rivers were way up. One of the reasons I chose putting the observatory on piers instead of a floating slab was I did not want to build my site up enough to get good drainage away from the building. I felt I could just let the water run under the building by elevating it.

We got over 6 inches of rain in a month. I live in an area that normally gets 30 inches of precipitation in a year. After pouring my tubes the rains returned. It rained and rained and rained. My site was so wet that even with tubes buried 4 feet down, they were unstable. I had a pole barn full of lumber and started thinking about using it to build an ark instead of an observatory.

This was the low point of my build. I had serious doubts about success.

I knew I had to keep water away from the site. I dug two trenches to divert water away from the building site, lined them with landscape fabric, and filled them with sewer rock. I also covered by building site with thick plastic sheeting and covered it also with the same rock.

Luckily my skid steer neighbor also owns a small dump truck. He let me use it to haul the rock and I spread it with the tractor. This work was done in one long day.

[Joe Timmerman]

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Finally in the last week of June, I was able to start construction of the wooden foundation. The rains have let off and the site is dry. I have a vapor barrier installed and the diversion ditches and base are covered with rock.

The foundation is 2 x 8 treated timbers mounted on 4 x 6 (actually 3.5 x 5.5) posts. Even with trying to level the tops of the sonotubes, I still had a slight differential in the tops of the tubes. I leveled everything by mounting everything to the posts. I have a double beam running down the center. Joists are 16 inches on center all attached with joist hangers.

This part is easy and fun.

[ChuckWalters]

Just one word to describe it. Incredible!