Moving pier....any advice please.

[paul mc c]

Hello all,i have built an observatory which houses a permanent pier.Origionally every thing was built with a Meade lx 200 12" sct in mind,but i have replaced this set up with an NEQ6 Pro and 9.25.

My problem now is because the latter set up is far lower than the Meade i now have walls that are to high,restricting my view greatly.

I have raised the top plate to a point that there is vibrations now,so my only option is to move the pier.

Now the pier is set in concrete about 18" below the surface so and the pier has a plate attached to the bottom.

I will have to dig the pier out and here is my worry,when i break into the concrete, there will obviously be a hole in the footing,if i fill this in and extend the concrete by maybe 18",would this be ok to now bolt the pier into the old and new concrete......hope this makes sence.

I have attached pic of origional to help....also i will have to move the pier towards the wall in second pic.

Paul

[saac]

Paul I think that would be absolutely fine. The design criterion for the pier foundation is the mass of the foundation block for stability and vibration damping. The load bearing capacity of the concrete block far exceeds anything that will be asked of it so there is no need to be overly concerned with respect to that. So long as you ensure that your "patch" or "insert" is bonded to the original block it will be fine. You may want to try and chisel an undercut into the original block so that your infill has something to bite against. Alternatively, if you are concerned about movement, you could pin the new overlay of concrete infill to the original block. Drill some holes in the original block and fix rebar or threaded rod, leave the rods extending and infil with your new concrete. This is the same technique used when adding an extension to a house - the new sub is pinned to the existing footing - it bonds the two mass blocks together .  To be honest, if it were me, I would just use a sufficient back-fill of new concrete without pinning but undercut the original sub to ensure good bonding; the loading is very low.

Jim

[paul mc c]

Thank you Jim,thats what i was hoping to hear,when you say "bonded" do you mean with primer such an Unibond.

[saac]

I wasn't thinking anything as sophisticated as that  Paul, although I believe there are preparations that you can use to help ensure a good concrete to concrete bond (Travis Perkins etc may help). I was really just meaning that you will need to get good contact between the old and new concrete infill - if you just undercut it by chiselling out some of the old foundation so that the new concrete can get in and bite on something as it sets.  I guess your big challenge is going to be access to swing a mallet and hold the chisel.  I'm going to be doing exactly the same as you next summer - I need to move my pier back a little. I'm a bit luckier in that my pier was bolted to the pad but I'm still going to need to lay another slab of concrete to extend the foundation.  Good luck with it - are you going to be doing before the cold set in ?

 

Jim 

[paul mc c]

See what you are saying Jim,yes i will roughen up the edge for good contact,i was planing to drill around the pier first and hopefully that will make it easier to break up.

Yes i will hopefully try and get it done soon if i can get the time,i dont really have to worry about the weather as i can work inside the observatory.

[Adam J]

You don't have to mess about with moving the pier. Just go to a local fabricator and ask them to make an extension for you and provide them with a drawing for the holes on the top place so you can mount it directly to the current one. That is what I did when I made mine a little too short, cost me 100 pounds. 

[paul mc c]

I am throwing out this idea to solve my dilema,i hate the thought of digging the pier up and moving it,and want to keep the cost down,i was thinking could i attached a concrete section,with 4 threaded rods through the concrete and extended beyond the bottom and then bolting this section to the existing pier plate.

The new concrete piece would probably be around 24" in length,and same width as the pier,could this work.

[Swoop1]

Instead of extending the height of the pier, why not remove the pier form the concrete base and raise the level of the base with a further pour?

Bonding to the existing base could be achieved by ensuring the old base is cleaned up and then providing a 'key' for the new pour to bond to. Back in my post school days, I did a 1 year course for scaffolding at a civil engineering college. This included aspects of other trades so that we knew what we were scaffolding for. One module was for concrete pouring. We had to prepare exisiting floors for another layer of concrete and I got to play with scabblers, compressed air machines whioch had multiple hardened steel pistons that impacted the concrete floor and roughned the surface. This gave a good key.

[paul mc c]

Yes I am going to remove the pier and re-fill and extend the footing and bolt the pier to the new fill,I think this is the best way to go,as it should keep vibrations to a minimum.I will, as you say clean the older concrete before I pour the new concrete.Hope to do it next week.

[bottletopburly]

8 hours ago, paul mc c said:

Yes I am going to remove the pier and re-fill and extend the footing and bolt the pier to the new fill,I think this is the best way to go,as it should keep vibrations to a minimum.I will, as you say clean the older concrete before I pour the new concrete.Hope to do it next week.

Beware of the frost ,and cover over once done.

[paul mc c]

2 hours ago, bottletopburly said:

Beware of the frost ,and cover over once done.

Should be OK there,I will be inside the obey working on it.

[paul mc c]

I finally got to work on removing the pier.......hope never to have to do this again,thought I could drill lots of holes and chip away with a hammer and bolster,how wrong I was,ended up having to rent a kango hammer and 8 hours later finally got the pier out....I will refill the hole and put an extra 3"topping on the whole block of concrete and drill for threaded rod and resin them in and this will be me sorted.