Pier failure
Some time ago we wrote an article about one of our observatory piers had become loose with cracked concete and that we had patched it with liquid concrete patch last summer. Well, it did not fix it and yesterday we decided to pull the pier and convert the area into a Dobsonian scope visual observing area instead of a small schmidt on a pier scope. It came out easier than we thought… that was the bad news. Here are images of the results: total wood rot.
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The pier was 2×4 pressure treated wood assembled, glued and screws together leaving a hollow core.
It was dug into the ground as far as we could go on residential lot fill (lots of rock and stone), maybe 2′ with a lot of post concrete in with it. After that the hollow core was filled with sand to help reduce and damp vibration and add some mass. We believe that the problem was both the cracked concrete and very high water tables in the spring. This pier was installed in the fall of 2002 and has been subjected to water over and over. The fear now is the sister pier, about 6′ away.
So… moving along quickly, we still wanted to repurpose the robodome area. So we removed the robodome patform, cleaned up the area and reused the rotted pier by trimming the bad stuff off, cutting 1/2: off each side and inserting it into the larger 2×6 constructed in ground pier that was used for the 20cm lx200 in the robodome.
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It was a tight fit, then secured with eight 3″ screws on all four sides. The top was removed and filled the hollow with sand again. Today’s jobs include a new coat of varathane and some silicon sealing around the interface between old and new piers.
We plan on putting another Schmidt-Cass scope on it dedicated to astrophotography. The buried PVC conduits bring 110vac, usb and 1 serial cables from the observatory.
The last piece of the picture is to design and build a wood box large enough to cover the scope, similar to a design we have seen in some past issues of Skynews, or Sky&Telescope … sometimes in the last 5 years 🙂