# Forum Home Renovation Retaining Walls  Retaining Wall Posts in Sandstone

## SLUGGO33X

Morning All, 
I need to build a small retaining wall (400mm high x 6m long) before i pour a concrete slab for an eventual carport. Only problem is the site is sitting on a massive sandstone rock shelf, approx 100mm under the level i have excavated.   
I will be using 200x75 TP sleepers for the wall and was planning on using the same for the posts before i hit the rock. If i decide to still use the sleepers as posts, what is the easiest way to dig the post holes in the sandstone... jackhammer and a steel bar? Any tips on getting a nice clean hole? 
The other option which i just thought of was suitably sized steel rods embedded in the rock. Would it work? If so, what size rods, spacing, how deep, and how to get the buggers in?

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## Bleedin Thumb

Slugo, if your wall is only 400 high AND you have a concrete slab infront of the bottom course don't worry about using uprights.
Just lay your sleepers out (on the flat) stretcher bond and nail each sleeper with 3 150 x 6.25mm landscape nails. 
OK you are using more sleepers than if you had them on edge but its still cheaper than digging in rock. 
If there is going to be some issue that could cause the wall to fail ie cars parked up there, then you may have to rethink my advise or use deadmen or something.

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## SLUGGO33X

Beedin Thumb, no, there will be no cars parked on the high side of the wall, it's just holding back the heavy clay based dirt. 
A couple of questions... 
I was planning on constructing the wall using the sleepers on edge with posts set in the rock prior to pouring the slab, so that it would also act as permanent formwork. Can i still do the same if i use your option?  
Also, as there is nothing securing the wall to the ground what's stopping it from moving laterally? I'm assuming i can't backfill till i pour the slab as the weight of the dirt will just push the wall over? 
Do i still put a batter in the wall if i lay the sleepers as you suggested? 
Sorry for all the questions, but as i hadn't considered your option i want to make sure i have all the answers before i start. i do like the idea of not having to dig in rock  :Biggrin:

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## Bleedin Thumb

> Beedin Thumb, no, there will be no cars parked on the high side of the wall, it's just holding back the heavy clay based dirt. 
> A couple of questions... 
> I was planning on constructing the wall using the sleepers on edge with posts set in the rock prior to pouring the slab, so that it would also act as permanent formwork. Can i still do the same if i use your option? Its getting the posts into the sandstone that is the problem. 
> Also, as there is nothing securing the wall to the ground what's stopping it from moving laterally? I'm assuming i can't backfill till i pour the slab as the weight of the dirt will just push the wall over? When you lay sleeper on the flat you usually bury the first 1 or 2 courses and spike them into the ground with 12mm reo You won't be able to spike them so I would be very tempted to put deadmen in on your second course IE sleepers going perpendicular to the wall back into the fill. You have to make sure that the deadmen doesn't settle over time so I would pack the end of the sleeper onto the rockshelf with some off cuts. By using deadmen the weight of the fill holds the wall in place. You can also use a plastic geogrid soil reinforcement mat for this - see if your local landscape supplies will sell you 6 m worth - this is better than using deadmen.(its the stuff they use on gravity block retaining wall systems)  
> Do i still put a batter in the wall if i lay the sleepers as you suggested?No just go straight up. 
> Sorry for all the questions, but as i hadn't considered your option i want to make sure i have all the answers before i start. i do like the idea of not having to dig in rock

  Hope that helps :Smilie:

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## SLUGGO33X

> Quote:
>                          <table width="100%" border="0" cellpadding="6" cellspacing="0"> <tbody><tr> <td class="alt2" style="border: 1px inset ;">                                                   Originally Posted by *SLUGGO33X*   _Beedin Thumb, no, there will be no cars parked on the high side of the wall, it's just holding back the heavy clay based dirt. 
> A couple of questions... 
> I was planning on constructing the wall using the sleepers on edge with posts set in the rock prior to pouring the slab, so that it would also act as permanent formwork. Can i still do the same if i use your option? Its getting the posts into the sandstone that is the problem. I was actually asking if i could still stand the wall up prior to pouring the slab, not the use of the posts. Your suggestion of the deadmen back into the fill answers this question.  
> Also, as there is nothing securing the wall to the ground what's stopping it from moving laterally? I'm assuming i can't backfill till i pour the slab as the weight of the dirt will just push the wall over? When you lay sleeper on the flat you usually bury the first 1 or 2 courses and spike them into the ground with 12mm reo You won't be able to spike them so I would be very tempted to put deadmen in on your second course IE sleepers going perpendicular to the wall back into the fill. You have to make sure that the deadmen doesn't settle over time so I would pack the end of the sleeper onto the rockshelf with some off cuts. By using deadmen the weight of the fill holds the wall in place. You can also use a plastic geogrid soil reinforcement mat for this - see if your local landscape supplies will sell you 6 m worth - this is better than using deadmen.(its the stuff they use on gravity block retaining wall systems). Great suggestion on the deadmen, cheers!!  
> Do i still put a batter in the wall if i lay the sleepers as you suggested?No just go straight up. 
> Sorry for all the questions, but as i hadn't considered your option i want to make sure i have all the answers before i start. i do like the idea of not having to dig in rock_ 
>                       </td> </tr> </tbody></table> 
> Hope that helps

  Cheers mate, off to the timber yard now. Just hope this rain in Sydney stops as the kids now have a temporary pool where i have excavated! damn clay!!

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