Can retaining wall posts be bolted to bedrock?

[Mason67]

Hi Everyone, 

I'm planning to build a retaining wall and the height is 1m. I'm planning to dig holes 800mm deep but unfortunately some of them happened to be right on the bedrock and I can't go deeper than 100mm which is not enough. so I'm guessing my only option is to drill holes in bedrock and bolt down the posts using base plated posts or similar methods. 

is this the only option available? is there any other methods? 

Thanks 

[Jewelleryrescue]

Hi @Mason67 

What  sort of retaining wall ? log besser brick? as this matters to  the strongest fixing method.

Well as a  bit of a  spoiler  what ever you  are  using it would be safe to  say drilling in 12mm reo rods verticaly into the stone to hold the base of the  wall in place.

With out seeing your site I would possibly like a besser brick wall  with concrete footings both thick and thin over the  bedrock with reo  rods 600 mm out of the rock  sticking up like a  porcupine into the besser cavities where you fill with cement.

For   CONVERSATION STARTER/

[Mason67]

Hey @Jewelleryrescue  Thanks for your reply. Sorry I forgot to provide any details. I'm planning to use timber posts and sleepers. previously built 3x retaining walls all with timber, all dug 600-800mm deep but this one is a bit tricky as it's right on a bedrock. 

I thought about drilling into bedrock and using reo bar but not sure how to level the base? is non shrinkable cement ok? 

Cheers 

[Jewelleryrescue]

Hi @Mason67 

The way i see it is  surface attaching a timber to bed rock is doable but not very strong as a retaining wall is holding how alot of earth and doulde the weight when  wet.  Whats the hieght of the wall out of the ground.? To jugde forces involved?

Basically you or  i could kick the post over. in 100mm of soil on top over rock bolted on. Plus it is hard to attach  reo rods to timber post in a strong way. I think you get what i mean.

Another option is to jack hammer post holes into the bed rock 400 mm down would near hold a  mountain once cemented in.  This  might be the best option hire a medium size  jack hammer a pointbit  and chisel  bit.   This way no reo  rods  need or brick work. And it suits your timber building style and is strong as anything.

Whats  your thoughts.?

Whats the wall holding back? What height?  as I am thinking  heavy duty retaining wall but you may not need that level of  support if you  can get two deep posts each side of a bed rock  amiddle post may not need super strenght

[Mason67]

Hi @Jewelleryrescue ,

Great information mate. the height of the retaining wall from the ground is 1m but it's not holding so much earth. there is another retaining wall 1m away from this one but on a higher level as we are on a hill. maybe a picture could help to visualize. 

I have a mid size jack hammer. it was easy to break sandstone but the rock that I'm dealing with now  feels very hard and impossible to break. 

current depth in 3x of post holes is 100mm. I don't think if I can get to 400mm considering how hard this rock is. 

[Jason]

Hi @Mason67,

Let me extend a very warm welcome to Bunnings Workshop. We're pleased to have you join the community. 

Great to see you getting fantastic advice from @Jewelleryrescue. I'm sure he will get back to you as soon as possible.

Our resident Bunnings D.I.Y. experts would typically be also very keen to share their thoughts but both are unexpectedly out at the moment. Hopefully they will be back on board very soon. Let me see if @JacobZ95, @Nailbag or @DIY4Knuckleheds might be able to join in the discussion in the meantime.

Jason

[JacobZ95]

Hi @Mason67,

You're bang on the limit of retaining wall height before you need building approval so I'd be looking to over engineer this just to be safe.

If removing the bedrock is too difficult, which it sounds like it might be, I'd drill holes as deep as you can (ideally 400mm+) and insert M12 Threaded Rod epoxied in place using Reo502 Plus Chemset Pure Epoxy and attached to Pryda 100mm M12 Bolt Down Post Anchor. I'd even consider drilling two extra holes in the base of the post anchor to increase your attachment points.

Like I said though, this is right on the limit of what requires building approval so it might be worth contacting a professional for advice.

Cheers,

Jacob

[Nailbag]

Hi @Mason67 Your going to need the help of either a professional service or plant hire in order to break bedrock at any depth as any hand-held will not be suitable. You can hire stand behind Dingo's with breaker chisel attachments. I would then be inclined to use Gal sleeper "H" and "C" section uprights that don't require a large hole that sleeper ones will. These are available in a range of lengths from the outdoor timer yard. This will be a straight forward stronger solution that allows you to still use timber sleepers.

all the best, Nailbag.

[Mason67]

@JacobZ95  Thanks for sharing your thought on this. After doing some research online, this is what exactly decided to do but the idea of two extra holes in the base plate is great. Also because the surface is uneven I've been thinking to use some not shrink grout . Any advice on that ? Thanks  

[JacobZ95]

@Mason67,

You could definitely use the non shrinking grout for levelling if you wanted to, but a cheap technique often used with threaded rod is to essentially “sandwich” the baseplate with two nuts and wind the bottom ones up or down to find level, then tighten the top nut to lock everything into place.