Now that I have a pier (thanks Phil!), I need to start thinking about the footing. I've heard that you need at least 1 cubic metre, and then I've heard that you don't need anymore than 100mm deep. It's hard to know which advice to listen to, especially when what works for one might not work for another due to other variables.
So... how big is your pier footing? How would you describe the soil in which it sits (clay, sandy etc)? How often do you need to re-align your mount?
My soil is fairly sandy. I was more or less thinking of digging down until it got hard and using that as a gauge.
Depends on payload and size of mount, general rule of thumb is around one cubic meter. I found that too be a bit of a overkill for my setup and settled on 700mm^3.
I used 1 cubic metre each on all of my pier supports. In sand you will need to go fairly deep. Maybe go down to 700mm and see what is there.
I have not had to realign my first mount ever in 4 years since it was installed.
Great, thanks Paul :-)
Quote:
Originally Posted by Manav
Depends on payload and size of mount, general rule of thumb is around one cubic meter. I found that too be a bit of a overkill for my setup and settled on 700mm^3.
Thanks Yugant :-)
I'll be using an either an RC8 or an ED80 NEQ6Pro and I'm unlikely to be getting any bigger scopes, though I suppose I may upgrade the mount at some point. Not really sure what that weighs in total.
If my math is correct, I think 1m^3 will require roughly 1080kg of gravel, 720kg of sand and 360kg of cement, not to mention water. Man, that's a lot of hard work right there. My planned site isn't readily accessible to large vehicles so that would have do be done by hand (with a mixer preferably).
I might need to reconsider my planned site because I'm allergic to hard work ;-)
I am using only about .25 cu m.
But my soil is non existent and my sub base is granite covered by chocolate rock.
In two years it has moved not at all and it has no resonance even if I jump up and down on the ground near it.
It really is a matter of how well your bond is with the surrounding substrate.
Driving star pickets at angles into the hole base helps to increase integration
Can you get a small truck in there? Google "small concrete trucks".
You can get small pumps too.
Cheers
Thanks Chris :-)
Possibly, I'm not entirely sure. To be honest I didn't think we'd get the ute up there but the wife is confident we will and I'm a bit spatially retarded so maybe.
I didn't know about those small pumps, that could be a winner if we can get the ute up there with a trailer.
Might consider a site closer to the house that would be more accessible, but I might have to cut down some trees then.
Quote:
Originally Posted by jenchris
I am using only about .25 cu m.
But my soil is non existent and my sub base is granite covered by chocolate rock.
In two years it has moved not at all and it has no resonance even if I jump up and down on the ground near it.
It really is a matter of how well your bond is with the surrounding substrate.
Driving star pickets at angles into the hole base helps to increase integration
I think I might try something a little bit left field. I might try building the footing out of besser blocks and hebel. Should greatly reduce labour and be fairly cheap. If worst comes to worst and it proves ineffective I'll just cover it up and do another one nearby.
And of course now that I have everything dismantled, we have the first clear night (while I'm actually home) we've had in donkeys.
Do you have a soil report for your block? If yay then use that as a guide. Otherwise consult your local council and enquire about soil types in your area. have a look at this site. http://www.build.com.au/building-reactive-soil-sites
My site is only slightly reactive, and top soil is shallow. My footing will only be 600 x 600 x 700 deep. because it can be.
I think I might try something a little bit left field. I might try building the footing out of besser blocks and hebel. Should greatly reduce labour and be fairly cheap. If worst comes to worst and it proves ineffective I'll just cover it up and do another one nearby.
And of course now that I have everything dismantled, we have the first clear night (while I'm actually home) we've had in donkeys.
It's all about the mass, and block footings for a pier are not going to have the density of a solid block of concrete. Hebel blocks are aerated concrete.
Your going to have to dig the hole anyway, so why not use concrete. The big labour is in digging the hole. You can get concrete delivered and save on the mixing labour.
Do you have a soil report for your block? If yay then use that as a guide. Otherwise consult your local council and enquire about soil types in your area. have a look at this site. http://www.build.com.au/building-reactive-soil-sites
My site is only slightly reactive, and top soil is shallow. My footing will only be 600 x 600 x 700 deep. because it can be.
I don't, but that's a very good point. Thanks very much :-)
Quote:
Originally Posted by glend
It's all about the mass, and block footings for a pier are not going to have the density of a solid block of concrete. Hebel blocks are aerated concrete.
Your going to have to dig the hole anyway, so why not use concrete. The big labour is in digging the hole. You can get concrete delivered and save on the mixing labour.
All good points Glen, but the problem is I don't think I can get that delivered due to limitations in site access, as described above. Nearest water will also be 100m away (the dam, with no pump available to draw water to the site either), so there's a number of complications there.
I've seen this done with besser in the US, apparently without problems. I think there' more too it than just mass, there's going to be a lot of variables here. Inertia is important but only if there's forces acting on object. If the soil isn't very reactive I can probably get away with less. Additionally, who's to say that we actually need these massive 2000kg footings? Maybe similarly sized footings of 500kg is enough. I suspect we generally over-engineer things.
I'm going to give it a shot... if it proves ineffective you can tell me "I told you so!" :-)
Well I won't tell you that because my pier and footing are under spec according to the experts - good luck and try to use some star pickets in the construction if you can.
Well I won't tell you that because my pier and footing are under spec according to the experts - good luck and try to use some star pickets in the construction if you can.
Thanks mate :-) It might not work but it'll be cheap and relatively easy to try so I don't think there's a lot to lose.
That's one thing I meant to clarify above but forgot about. How is it best to integrate star pickets into the construction?
Minimum 1 cubic metre for astrophotography......visual......?
Cheers Tom
Sorry I'm not sure I understand exactly. Are you suggesting that minimum 1m^3 for astrophotography but visual you're not sure? Or are you asking whether I'll be doing AP or vis? If the latter I'll be strictly AP, with both an RC8 and an ED80.
Additionally, who's to say that we actually need these massive 2000kg footings? Maybe similarly sized footings of 500kg is enough. I suspect we generally over-engineer things.
I'm going to give it a shot... if it proves ineffective you can tell me "I told you so!" :-)
I reckon you're pretty right about that. Unless you have a scope the size of a mule I'm sure something the size you're talking about will work fine.
Mine is in clay, so I went 1 cubic metre, over two years now It hasn't moved, and by the way the hard work is definitely digging the bloody hole!
Clear skies.
I reckon you're pretty right about that. Unless you have a scope the size of a mule I'm sure something the size you're talking about will work fine.
Thanks :-)
Quote:
Originally Posted by Neil
Mine is in clay, so I went 1 cubic metre, over two years now It hasn't moved, and by the way the hard work is definitely digging the bloody hole!
Clear skies.
Spot on there, digging the hole certainly wasn't fun! I've only gone 1100 square by 500 deep for the hole. Footing will finish about 100 above the ground, giving a total size of 1100L x 1100W x 600D.
Top 200-300 was nice, soft, sandy stuff, then we hit a layer with a fair amount of rock, below which was clay. Hopefully this'll do the trick, because even that size was hard enough yakka for an office slob like me ;-)
I have a local guy coming in to do the concreting tomorrow morning. He was going to get a truck in but after seeing the site he confirmed my suspicion that it wasn't possible and will have to be done by hand.
Turns out since starting this thread my mount has changed again and it'll now have an EQ8 sitting on top of it. For the moment I'm literally going to set the pier tripod it came with on top.
