# Forum Home Renovation Retaining Walls  Link block retaining wall on sloping ground

## dclayw

Thinking of replacing a sleeper retaining wall with link block, probably Tasman blocks. 
The exisiting wall is about 12m long and goes from zero height to about 1100mm. I couldn't find any info anywhere on how to go about building such a wall. Everything I've read assumes the base of the wall is on level ground, i.e. the first course of blocks is level. In my situation the first course of blocks needs to be stepped down all the way along the wall and I'm not sure how to go about it. 
The existing wall is also on the boundary and has a boundary fence bolted to it. One of the reasons I'm looking at the Tasman blocks is because they will produce a near vertical wall, (I want the wall to remain on the boundary). Are there any issues placing a timber fence on top of a link block wall. The posts would have to go in the drainage fill.

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## stevoh741

I replaced a rotton timber wall with tasman blocks quite similar to what you explain. I agree noone tells you what to do on slopes and it is near impossible to step a roadbase footing. You are better off with a concrete footing and use bits of sleeper to form the step-ups as you go up the slope. I use sleeper offcuts as they are 200mm high same as the blocks. Then a 10mm-20mm bed of screeded sand and start laying the blocks gently tapping into place with a mallet. If you get the bottom course/s level, laying is a breeze. Every 4 or so courses fill the blocks with 20mm darinage gravel and continue to top course. Make sure you use aggi pipe and drainage gravel behind wall and wrap it all in filter (geotech) fabric to keep dirt out of drainage. I put pool fencing on top of my wall and just concreted the posts in as deep as I could push them (bout 2/3 courses. Then just cut around them with a capping stone. Looks great and will last forever. Mine was bigger than yours and cost around $4000 to do myself. I had quotes in the vicinity of $12000 - $15000. (Charging like doctors to build a wall!!!)

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## dclayw

> You are better off with a concrete footing and use bits of sleeper to form the step-ups as you go up the slope. I use sleeper offcuts as they are 200mm high same as the blocks. Then a 10mm-20mm bed of screeded sand and start laying the blocks gently tapping into place with a mallet.

  I think I know what you mean but is it possible for you to post a pic, or perhaps a diagram?   

> I put pool fencing on top of my wall and just concreted the posts in as deep as I could push them (bout 2/3 courses. Then just cut around them with a capping stone.

  So you put the fence directly on top of the wall? That would be the way to go for me as the fence would then be on the boundary, but I'm not sure if I can do that with a 5-6' timber paling fence. I'm thinking I might have to place the fence just inside the wall, in the drainage gravel. I'm not sure if that's even recommended, fence also wouldn't be on the boundary.    

> Mine was bigger than yours and cost around $4000 to do myself. I had quotes in the vicinity of $12000 - $15000.

  Can I ask how high your wall is at its highest point, how long, how many sqm. Did you use geogrid? 
I agree about the quotes. My wall is actually about 7.5sqm and the quote I got for a gal steel post/concrete sleeper wall was $11,500.

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## cherub65

You be best with core filled retaining blocks as fence posts can be concreted in blocks, (Gal posts). The wall your considering is not suited to having boundary fence set in nor behind in fill

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## dclayw

I understand that it will not be possible to place the fence on top of the wall but can you outline why it's not suitable to to place the fence posts behind the wall.

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## stevoh741

> I think I know what you mean but is it possible for you to post a pic, or perhaps a diagram?  Similar to this pic i found on the net. use the 200 high sleeper at the face of each step up. 
> So you put the fence directly on top of the wall? That would be the way to go for me as the fence would then be on the boundary, but I'm not sure if I can do that with a 5-6' timber paling fence. I'm thinking I might have to place the fence just inside the wall, in the drainage gravel. I'm not sure if that's even recommended, fence also wouldn't be on the boundary.   You won't be able to use timber posts as they are too big. In the drainage or directly behind the drainage will not support the posts. If you use pool fencing you can jamb the (50mm x 50mm) posts into the hole of the blocks and it should force down about 2/3 courses then fill around it with concrete. I prob wouldnt do this with gal posts and a timber fence as they wont go deep enough to support the weight, whereas an aluminium pool fence weighs bugger all. Away from the posts is fine to core fill with gravel as per literature with tasman blocks. 
> Can I ask how high your wall is at its highest point, how long, how many sqm. Did you use geogrid?  wall is about 15m long and goes from about 600mm high to 1500 high. Use geogrid every 2/3 courses if wall is above a 1m but also if it is above 1m you will need council approval. Check literature with the Tasman blocks for exact spacing for geogrid. 
> I agree about the quotes. My wall is actually about 7.5sqm and the quote I got for a gal steel post/concrete sleeper wall was $11,500.

  some retaining wall builders are thieves..... :Eek:

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## dclayw

Thanks for the pic. 
My situation will be pretty similar to yours. Just wondering if it would be advisable to embed the first course into the concrete footing rather then a 10-20mm bed of screeded sand on top. I'm thinking that because the footing is sloped there might be a chance that the bed of sand could get undermined by water. 
By the way Boral document that it's possible to place a fence on top of their keystone walls, and even place the posts behind the wall as long as they go down 700mm and are encased in concrete. Ofcourse the engineering would need to be looked at more closely. Keystone blocks are not too dissimilar to Tasman, in concept anyway.

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## cherub65

> By the way Boral document that it's possible to place a fence on top of their keystone walls, and even place the posts behind the wall as long as they go down 700mm and are encased in concrete.

  
Placement of fence post in there documentation relates more to guard rails with no wind load

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## stevoh741

> Just wondering if it would be advisable to embed the first course into the concrete footing rather then a 10-20mm bed of screeded sand on top. I'm thinking that because the footing is sloped there might be a chance that the bed of sand could get undermined by water.

  
the footing should be level and the step ups give the height to get up the slope. Once the first course is layed on the bedding sand it should be about 100mm below finished ground level (check documentation for exact depth). Once backfilled, the earth helps hold in the bottom course and the sand and blocks cant go anywhere.

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