Tower accomplished- now, how to mount to solid rock?

[VK3QI]

Brian,

In all seriousness, have you considered an entirely different alternative for your proposed foundation?

An above ground pad footing with rebar and cage to fit the base of the tower you have.

A back of the envelope calculation using 12 metres for the tower height and a typical tribander antenna, would suggest a reinforced pad approx. 2.0 mx by 2.0mx by 0.5mx thick.

This equates to 2 cubic metres of concrete which is not all that expensive when compared with the costs associated with drilling.

Obviously you would need an engineer's calculations if a permit is involved, but then you will also need similar calculations for your proposed rock anchoring, especially the method by which you attach the anchors to the plate you have shown.

I have even seen Nally towers installed that way and in fact Nally towers now offer a similar pad style foundation arrangement (albeit installed below grade).

Cheers

Peter VK3QI

[VK2AAF]

Hi Peter,

No, I hadn't considered a surface mounted concrete pad, mainly due to the amount of concrete involved.

There's no way to get a concrete mixer truck to the tower site. 2m^3 would require a concrete pumper truck. Nearest truck access point is about 25m to the pour site and it would be pumping uphill 6m. Last time I priced concrete for a driveway, it was about $235m^3, but that was a simple pour with standard mixer truck access. Pumping would be a bit more.

Option B would be 108 x 40kg bags of dry mix concrete (54 per m^3) at $7.70/ea = $831.60... and very little chance of a homogeneous set.

Pinning the stick to the bedrock looks comparatively cheap.

73 de Brian

[VK3QI]

No worries Brian,

Just a thought - but with restricted access that is a no goer.

Good luck with the drilling.

Cheers

Peter VK3QI

[VK2AAF]

Thanks for the suggestion anyway, Peter. All part of life up here in the Blue Mountains. We ♥ the terrain but it often poses challenges!

73 de Brian

[VK7DX]

Hi again Brian,
If you rebolt the 3 plates/stubs back onto the tower and refit the 3 lengths of tube that were holding the 3 base plates together.
Once bolted then weld them so they cannot move then you can weld the rebar/thredded rod to each base leg.Then you can unbolt from tower.
You now have a base that can be fitted to holes for grouting,level with spirit level and grout,if when tower is fitted its not plumb thin steel can be
fitted between top and bottom plates for final adjustment.

Looks like the petrol drill is your best option for the holes.

Grout is about 3 of sand and 1 of cement,you will only need about a barrow of sand and a couple bags of cement.

Hope you can follow what I mean.

cheers
Frank

[VK2AAF]

Hi Frank,

Oh, OK, I do see what you mean. Great ideas. That sounds like the plan!

Really keen to get the stick in the air & whack up a decent 10m Yagi. Working Ken VK6AKT in Perth at the moment with a temporary dipole hung between some trees at only 2m above ground. Deep, slow QSB, tho. Using 100W, could probably do with a lot less with a proper antenna.

Thanks again for all your help!

73 de Brian