Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Ground Work Question


Nigella Bryant

Recommended Posts

Hi all, just a question re: ground work for observatory. Back ground is that I've a pulsar 2.7m dome, full height wall which is going to be relocated at my new home. Previously this was on a circle of brick with wooden floor and central pier of concrete. Now my new overgrown garden has a bank where my observatory is going to go. I could build on the bank a complete wall and infill and level with concrete or I could just lay pillars of concrete and blocks 18inches apart and put a wooden level structure on top where the dome would go. 

It's not a question that needs to be answered quickly but trying to get my head around clearing the garden in the next few weeks and which way would be best.  I know the centre will be on footings and block for the pier but other than that I'm open to suggestions. 

I hope this makes sense to everyone. Thanks for reading.

Link to comment
Share on other sites

I suppose  a lot depends on the slope- what is the difference in ground level between the two opposing sides of the dome?

Three options-

1) Dome on a platform that is fixed at the high point of the slope and the rest is supported by stilts. Place your pier in the optimal position. Once the position is identified, Build the platform around it and park the dome on top. Downside is that the pier could be quite long.

2) Partially dig out the bank and build up the slope using the spoil, perhaps with a retaining wall around the dug out arc. Then assemble the dome on a platform laid on the flattend area.

3) Dig footings in a square/ rectangle depending on what suits your obsy shape, build a brick/ block box that overcomes the slope, pier in the middle, concrete joists accross the box and build ypur obsy on top.

Whatever you decide to do, good luck and I'm excited to see your progress.

  • Thanks 1
Link to comment
Share on other sites

Thanks swoop, the slop is quite severe as there's a road above separated from my garden by a hedge, from garden level to road I'd guess I'm looking at 7/8ft difference. The bungalow is in a dip. It slops from the road/hedge to flat garden area. I've got about a 12ft slope. Hope that makes sense. 

Link to comment
Share on other sites

I think you should focus on the pier, not the dome. It is likely to be the limiting factor.

The dome can be supported on stilts, partly cut into the bank or whatever. It is in effect a tea-cosy plonked over the important bits.

So pick your pier location from the point of view of accessing the sky. What will give you the largest unobstructed view and shielding from lights? Then what is the slope at the point you want to install the pier, and what type of pier do you have in mind?

So for example if you have a 2.7m dome and a 1 in 2 slope (severe!), the drop from one side of the dome to the other will be 1.4 metres. A centrally mounted pier will extend at least 0.7 metres below the obsy floor.

If the local slope is 1 in 4 you still have a pier that extends between 35 and 40 cm below the floor.

If it is a self contructed pier (drain pipe or whatever) you can handle that. Level decking on stilts will then create a base for the observatory. Simple steps will provide a safe access route (something to consider as you don't want to slip and fall trying to get into the obsy in the dark and possibly on wet or icy ground.

If it is a bought pier it is unlikely to be long enough. Therefore you will need to build up from the ground block to a level where the pier is long enough, or construct a wall and a level platform. I have seen that kind of terracing done to mount an observatory, but it is a major civl engineering project, even if you have the skills or a freindly neighbour with a digger.

I think the deck on stilts to cope with the slope is the faster and cheaper approach as long as you can figure out how to get the pier up to the right level.

So my thoughts would be:

  1. Decide where you want to put the pier
  2. Measure the local slope
  3. Determine how long the pier needs to be to reach a level obsy floor and work out if that is achievable for the pier type you want to use
  4. Unless you want to create a permanent terrace for some other reason - go for decking on stilts if possible

Since the observatory does not touch the pier it does not matter if the decking flexes slightly or settles a bit.

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

Thanks old eye's, I'll be building my own pier as I've done that b4 and I've a metal plate to use for the mount. My thought is decking on stilts as you have suggested as the easiest and cheapest way forward. 

On clear night's I'm going to stand in the garden to evaluate where best to put the pier. Neighbours may well freek out, lol. 

It's great to be able to bounce off other's in this forum. 

Edited by Nigella Bryant
  • Like 1
Link to comment
Share on other sites

7 hours ago, Nigella Bryant said:

Thanks old eye's, I'll be building my own pier as I've done that b4 and I've a metal plate to use for the mount. My thought is decking on stilts as you have suggested as the easiest and cheapest way forward. 

On clear night's I'm going to stand in the garden to evaluate where best to put the pier. Neighbours may well freek out, lol. 

It's great to be able to bounce off other's in this forum. 

You are very welcome. I have had loads of support for my obsy build from the wonderful people on SGL.

  • Like 2
Link to comment
Share on other sites

You could depending of your situation build a cheap block U shaped wall into the slope to support half the dome and then dig out the other half and use this to back fill inside the wall construction. I am sure this has a specific name buts its been a while and I have forgotten the name.

  • Thanks 1
Link to comment
Share on other sites

I'm thinking that digging out the bank would mean having to shore it up somehow which could mean a lot more work, so I'd agree that decking on some sort of supports would probably make life easiest -- blocks or posts set on croncrete pads might be most reliable, though not particularly attractive unless you hide the blocks somehow.  Some could probably be set into the bank if you didn't want the deck to intrude into the flat garden space so much.

My own observatory is built on a slope, though nowhere near as steep as yours.  I poured six concrete blocks (about 500mm square at the corners, narrower in the middle of the long sides) using shuttering above ground level and rested the timbers for the floor on top of those (wrapped in DPC material where they're in contact so damp from the concrete can't reach the wood).  I dropped in lumps of rock and bits of broken concrete block as I was pouring so I didn't need quite so much concrete.  For, say, a 3m square deck or thereabouts I reckon you'd only need supports at each of the corners as long as you used deep enough timbers for the decking joists.  I have three piers attached to three further concrete blocks just below the floor level with a bit of EPDM sealing the gap between the floor and pier.

I guess you may need to put something over the decking (12mm ply?) inside the dome if you want to lay rubber floor tiles or anything like that.  Could be worth having a look at what upahill did with his build on a deck.

You probably would need a decent way to seal the time to the decking, to stop rain being driven underneath.  Though rain is so rare in the mediterranean climate we have down here in the south west that such precautions may not be necessary at all.

James

  • Like 1
Link to comment
Share on other sites

Sketchup has proved popular for designing observatories.  Quite a few of us started with that.  It's a bit of work to get the hang of initially, but then pretty much any 3d design program is going to be.  I'm using FreeCAD for designs for 3d printing now and that has an architectural module, but I've never actually tried using it.

James

  • Thanks 1
Link to comment
Share on other sites

Looks like a nice project to keep you busy!  I have a 1 in 8 slope on my garden.  When I put up my 2.1m dome I bit the bullet and dug the bank out.  It made life easier when it come to laying a concrete foundation and also kept the height of the dome down relative to my neighbour’s garden (she was really good about it all but even so, I didn’t want a stark white dome towering over her fence!)  My better half also gained a flat area for her greenhouse, but we did lose the strawberry patch!   I was in the process of putting some terraced raised beds in so the spoil/soil went in there.  If you do go down the dig-out route then that’s the biggest problem.  It’s amazing how the volume of spoil seems to quadruple compared to the size of the hole it came out of!

  • Thanks 1
Link to comment
Share on other sites

My ground slopes too and I dug it out rather than building up.  It was a mistake as the hole fills with water in heavy rain and I need a sump pump to clear it out.  I too didn't want the observatory too high but for my own benefit in the view from my living room rather than neighbours which are cattle.  With neighbour's fields on three sides the height made little difference to the astronomy.

Nigella, I guess it depends on what trees you can clear and hence the view from the pier.

Edited by Gina
  • Thanks 1
Link to comment
Share on other sites

Position 2 looks to be less work and further away from the Bushes, though you might be removing them.  Difficult to visualise without actually being there. 

I'd go for the flattest location it will be less work and less to maintain.

Carole 

Edited by carastro
  • Like 1
  • Thanks 1
Link to comment
Share on other sites

I'd also think about some of the trees you have around the site, that may not be obstructing the view now, but in a few years.

Also if you go for the 'bottom' of the slope, I'd arrange some form of drainage, even if its just a simple soak-away

  • Thanks 1
Link to comment
Share on other sites

I'm inclined to think that position 2 is better as well, but it's hard to say given the amount of vegetation.  If your new home is a house rather than a bungalow then perhaps a photo from an upstairs window might give a better overall idea of how that part of the garden looks.

I imagine it will all look a lot better once you've cleared the area a bit, too.

James

  • Thanks 1
Link to comment
Share on other sites

Thanks all, I guess I'll know more when I clear the garden of rubbish, brambles and the like. The hedge is conifer at least 9ft high from my side and 7ft high from the road side, looking west, but it's half dead so I'm inclined to chop at least 3ft off from my side. I've no near neighbours the side where I'm planning on putting the dome. My property is a bungalow so if I put it in position 2, it would look over the roof east wards. It's really complicated isn't it on where best. Supposedly clear here Monday night so I'll plan to sit in those two places to see what I can see. Neighbours might freak out, lol but needs must. 

  • Like 1
Link to comment
Share on other sites

Conifer hedges can be a nightmare when they've got too big.  If they subsequently get trimmed back beyond what is green some species won't grow again from the older wood because they don't have dormant buds like many deciduous trees do.

James

  • Like 1
Link to comment
Share on other sites

3 minutes ago, JamesF said:

Conifer hedges can be a nightmare when they've got too big.  If they subsequently get trimmed back beyond what is green some species won't grow again from the older wood because they don't have dormant buds like many deciduous trees do.

James

We had some dwarf (?) conifers by the road in front of our house. After 30 years they were definitely no longer dwarf and getting dangerously close to the power lines, although they provided a fine screen for the front garden and a popular nesting site for our local birds.

Along came our local electricity DNO and chopped off the top third. It looked a bit weird for a while, but they bushed out over time and now look like perfectly nice fat raounded conifers. I am sure it depends on species, but these were happy after a very severe haircut.

  • Like 2
Link to comment
Share on other sites

10 minutes ago, JamesF said:

Conifer hedges can be a nightmare when they've got too big.  If they subsequently get trimmed back beyond what is green some species won't grow again from the older wood because they don't have dormant buds like many deciduous trees do.

James

Hi James, I think it's dead half way down as there's only growth the road side and near the top. I might end up just leaving the main trunks, cutting off the branches and weaving branches cut off the pear trees to make a new lower hedge and put clematis to weave in and out. 

Edited by Nigella Bryant
Revised content
Link to comment
Share on other sites

30 minutes ago, Dr_Ju_ju said:

I'm no horticulturist, but I suspect that if you cut the tops off, there will be no re-growth from the bottom, effectively killing the trees....  which may or may not be such a bad thing ??

Yeah, I think the only way to go is lop, there's not much growth so I'd be left with dead trees probably in a few years anyway. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.