Pier pad requirements

[The_bluester (Paul)]

Following a few other people's efforts I have been thinking more and more bout putting in a pier for my Celestron CPC scope. Most people seem to have gone a different direction to what I was thinking to set it in the ground though. I was looking for any advise if I might be opening myself up to potential problems.


My plan was that next time we hire a dingo digger for works around the place, use the auger to make a 600mm hole for the pier of around 800mm depth to directly set the pier in concrete. Will that be an adequate and movement/vibration free way to set a pier in the ground or would I be better casting a larger pad and bolting the pier on top?

I was thinking to keep the concrete away from vibration inducing feet and to allow me to build an isolated floor right up to the post if I get to enclose it in an obs.

[el_draco (Rom)]

Originally Posted by The_bluester

My plan was that next time we hire a dingo digger for works around the place, use the auger to make a 600mm hole for the pier of around 800mm depth to directly set the pier in concrete. Will that be an adequate and movement/vibration free way to set a pier in the ground or would I be better casting a larger pad and bolting the pier on top?

I was thinking to keep the concrete away from vibration inducing feet and to allow me to build an isolated floor right up to the post if I get to enclose it in an obs.

Some people swear that bolting a plate to a pad does not cause vibration but others will disagree totally. Its your call. I am designing an observatory at the moment and will use a cavity under a wooden floor that will be isolated from the pier totally.... just in case.

Pier may be bolted to a concrete block or perhaps a "surefoot" anchor plate; not sure yet. I like the idea of zero concrete for a range of reasons including the obvious cost and environmental issues. I guess bolting a pier to a block means you can just bury the block if the scope goes or your needs change.

Good luck, its a time consuming process.

Rom

[ZeroID (Brent)]

The general consensus from the totally committed Astroholic is something like a 1 cubic meter reinforced solid cube under ground with an integral pier cast with rebo included to the mounting plate or a bolt down pad at the concrete cubes surface. Or similar, you get the idea.
I think the isolation issue is primary, keep pressure away from the scope support but the cube is a bit overkill. It seems to have been derived mainly in the USA where frost heaval of the ground subsurface is an issue.
A 600mm hole of 800mm depth would be pretty substantial IMHO dependent on the all up weight of whatever you end mounting at the top and the ground soil properties of the location. More information needed I guess.

[frolinmod]

Depth of footing is definitely based on depth of frost line. You want to go deeper than the frost line to prevent frost heave. Here where I am I have no frost and no frost line, so I could place the footing on the ground if I wanted to. A cubic yard (about 90cm X 90cm) of concrete is what folks around here pour for a pier footing.

[icytailmark (Mark)]

i just finished building my pier and i concreted my pier in the ground. Its just alot easier to do.

[The_bluester (Paul)]

No frost line to speak of here unless the winters get colder. It very occasionally snows here (only a couple of times in a decade)


For the foreseeable future it would mount my cpc925, possibly on a wedge. Perhaps down the track remounted on an NEQ6, but that would be about it, I am more interested in visual so there is no great value in building the ultimate pier for AP, but on the other side of the coin, if I put one in it might as well be solid enough to not be the limiting factor in AP with my existing gear.

That is one benefit I can see to boxing up and pouring a cube with the pier bolted to it. If I need a bigger pier later it is a simple unbolt and replace proposition.

[sheeny (Al)]

600 diameter x 800 deep sounds pretty good to me. Mine is 350 x 350 x about 700ish (but I stopped cause I hit rock).

The only issue you should have is if you have a clay layer below the bottom of the 800. If you don;t have that your pier should be fine.

Al.

[The_bluester (Paul)]

I could well find rock here too, plenty of it about.