Hi IIS'rs
Well a year in planning and research, the time finally came during the week for Nicky & I to begin the install of our pilot observatory. When researching IIS, CN, AM and a plethora of individual observatory sites, we kept seeing again and again, a reliance on the use of concrete for Observatory structure and Pier footings.
Its 2017, and I couldn't help but think there was a better way. While trawling youtube I found a video showing the installation of a wind turbine mast on Kangaroo Island here in Australia.
Sure enough no use of concrete for the mast footing, but something different.
I investigated more and found the Australian company that supplied the footings for the turbine project, - without concrete.
http://www.surefootfootings.com.au/
After speaking to them, and subsequently 4 different teams / customers that had utilised them for everything from house foundations building, light masts at sports grounds, wind turbine masts etc I bit the bullet and purchased some units.
We wanted to be sure that the footings would be vibration dampened, as well as free from any sort of harmonic vibration, and these fit the bill given their proven installation history working with Wind Turbines.
The observatory was to be located in a rural area, and we didn't have time for a soil test, so we figured we would have to experiment. All that was required was a 1800w Jack Hammer, 2Kw portable generator, extension cord, post attachment, and some elbow grease.
Oh and about 1 hour of our time for Nicky & I to get the whole job done!
We decided on 8 x SF 150 units for the Obs (4 x Walls and 4 x Roll Off - Roof Trusses) and 1 x SF500 for the pier footing. Each unit utilises 1600mm 2" posts for the driver posts. therefore my footings would be at least 1.6m deep per post, and generating a root ball of approx 3m diameter of stabilisation and security. The Obs walls and Floor are independent of the Pier Footing and Pier to remove any vibration or interaction between the two assemblies.
We opted for the SF 500 Pile Cap unit for the pier footing as it has to secure a Pegasus Pier as well as 160kg + of Mount, Telescope and imaging payload. The 500 units are rated for Up to 330kN. the SF100 Pile Cap units for the wall joists and Roof truss assembly are rated for 110kN. These footings are also removable, which you cannot say for concrete.
Each footing has a leveling plate so we could raise or lower the structure depending on the topology of the Obs site, or alternatively based on the Pier height required.
Step 1 - Attach Pier to SF500 and position. We used a Digital and an Analogue compass to make sure the footing was facing as close to true south as feasibly possible.
Tap 4 x posts in on corners with a mallet and get your jack hammer. Drive each corner in equally, checking the levels of the pier on the way. A laser level is handy here as well as a trusty square level.
Step 2 - Once all 4 corner posts are 1 foot from the base drive all the remaining posts in.
Step 3 - Remove the Pier, and drive the last remaining post straight down in the centre of the Plate for Torsional stiffness. The SF500 has 13 x 1600mm post securing the Pier into the ground.
Step 4 - Drive all posts flush to the guide tubes and Tek screw them in place. Each guide tube has 3 tek screws to secure the posts once driven in.
Step 5 - Reinstall the Pier on top of the SF500 plate, level, and you are done.
Step 6. Repeat as necessary for the other SF150's. these only have 4 posts each as they are load bearing for the Roll off roof truss assembly and walls for the Obs.
Lessons Learned.
1. Rock : Our greatest fear was hitting rock and finding that the 1800w jack hammer which we got from Bunnings wouldnt cope. We did discover though, that when we did hit rock (which happened 7 times), all we needed to do was give the post a good whack with a sledgehammer to break the rock, and then continue driving the posts in with the Jackhammer. We figured this out after struggling with the first 3 posts and realising we could be here all day!
I do believe at one point I exclaimed that the "instructional videos on the SureFoot website were BullS%$!" and there was no way we would get this done in an hour. We found the solution with the sledgehammer.
2. R&D : Dont be afraid to experiment. Everyone one we spoke to said to use concrete. The issue was that by the time you add up the cost for the concrete - especially of your obs is in a remote location, add in the formwork, add in the curing time etc we just found it was both time and cost prohibitive compared to our proposed approach.
3. Cost. I think all in including delivery to Sydney metro I was up for $700+ dollars and an hour of our time to install.
4. Next time: I would definitely recommend this approach, but would recommend a bigger jackhammer with more juice.