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Reply With QuoteThe weight of the soil will hold it forward, why concerned, it isn't your problem
Council retaining wall observations I regularly cycle along the Taralla Creek Trail here in eastern Melbourne, and council is progressively re-paving most of the shared path in concrete and constructing retaining walls and drainage where the edge of the path meets the creek. Being a nosy local I went down to check how the work's going, and I was surprised to see some big gaps between the back of the concrib sleepers and the inside of the universal columns. Most of these had been packed out with sparsely-spaced plastic wedges and what looks like standard framing pine. It's hard to tell if the pine is H3, but I sure hope it is because it'll be underground - it's certainly not white cypress though so it will rot eventually.
Anyway, this got me thinking - is it a problem to have this gap? Clearly over time this packing will dislodge itself (particularly the wedges) and the timber will rot, so the sleepers will just be "floating around" inside the web of the UCs. This probably isn't too much of a problem after the soil has settled with the active pressure of the backfill, but if things dislodge soon after the work is finished it seems like there's a good chance that someone standing on the top sleeper would cause it to rock back and forth. If this kept happening it could result in backfill leaking through the wall and various other problems.
Am I overthinking this or could this cause the wall to fail eventually?
I checked the plans for this wall (publicly available) and it looks like this gap in the back of the column was specified in the plans - sleepers are 80 thick, and there is 138 gap between the flanges (standard for 150 UC), leaving a gap of 58 which seems to be taken up by a 45 thick piece of timber and the remaining 13 with wedges. I have a few theories as to why this might have been specified but I won't bore you with those. The method of packing was not shown though so I'm a bit suspicious this work isn't really up to scratch.
Are there any engineers here who can comment on this? Is this standard practice, and will council ask the contractors to redo it? I'm just interested in the details of this as an engineering student and a DIYer.
The weight of the soil will hold it forward, why concerned, it isn't your problem
Not concerned, just interested as it seemed odd.
For future reference H3 is only rated for use above ground.It's hard to tell if the pine is H3, but I sure hope it is because it'll be underground
Gap is normal in 150 UC and wedges/wood chocks is to simply hold it in place prior to back filling.
Why? - without this measure there is a risk material can lodge in front of the concrete sleeper and without the sleeper fixed firmly and flat against the front inside of the 150UC, it compromises the strength of the sleeper and potentially voids the structural warranty on the sleepers .
Once its correctly back filled, compacted to minimise "heave", then they serve no purpose. Not an engineer but have built many retaining walls and is based on professional advice from a number of sources including sleeper manufactures
Once the timber rots, the gap will increase and allow more drainage. And if it is H3 it will rot soon enough.
I wonder why don't they save some metal and use U channel that fit the sleepers snugly, no timber nor wedges nor questions from nosy locals ...
Real knowledge is to know the extent of one's ignorance
Confucius
My assumptions would beOriginally Posted by Marc
Once the timber rots, the gap will increase and allow more drainage. And if it is H3 it will rot soon enough.
I wonder why don't they save some metal and use U channel that fit the sleepers snugly, no timber nor wedges nor questions from nosy locals ...
1 Smaller u sections would be less strength
2 Too neat a fit would make them harder to fit so any small amount of out of plumb/positioning would cause problems for installation.
3 Engineered to a certain strength see 1
4 The u sections suit all sizes of sleepers so less stock to carry.
Yes, makes sense. after all the small section that is perpendicular to the wall is the one doing all the work.
Real knowledge is to know the extent of one's ignorance
Confucius
Had a closer look at the supplied plans. This is a serious retaining wall - engineered and cost!!!
..."generally" speaking most average domestic situations can get away with 100 UC posts which can take 80mm thick sleepers (timber or concrete) up to 800mm above the ground and even 1200mm. For all the walls I've built as a general rule for the soil conditions they get concreted the same depth in the ground as they are above the ground and they never move. The cost of the posts average @ $35 per meter (uninstalled
These plans say 200UC posts.
...try lifting a meter of this stuff as its about 3 bags of cement 60kg and 4 times the cost per meter of 100UC.
This wall is engineered to have posts 4 meters into the ground and up to 2 meters above. They are cemented in 2.4 metres of concrete (if my calcs are correct 600mm x 4m).
My guess is each post would be 250 kg and ~ $800 per post, probably $4k to $5k per bay (Posts, sleepers, concrete, labour) not including drainage, rock and backfill. Big Job!
Guess it needs to be really tough with people cycling on it in groups.
Thanks for all the replies. Makes a bit more sense now.
Damn that's a lot of steel. Makes me wonder why they didn't just batter the clay and put up a railing and call it a day. Didn't seem to be any problems with erosion or instability before, but maybe it's just mitigation for flash flooding along the floodplain.
The shared path is set back from the edge of the wall so live loads shouldn't be a big consideration I think. Might be wrong though.
With public works they have to allow for higher traffic loads than on private property, so that's why it seems to be over engineered, It's just over 1m3 of concrete filling per post.Had a closer look at the supplied plans. This is a serious retaining wall - engineered and cost!!!
..."generally" speaking most average domestic situations can get away with 100 UC posts which can take 80mm thick sleepers (timber or concrete) up to 800mm above the ground and even 1200mm. For all the walls I've built as a general rule for the soil conditions they get concreted the same depth in the ground as they are above the ground and they never move. The cost of the posts average @ $35 per meter (uninstalled
These plans say 200UC posts.
...try lifting a meter of this stuff as its about 3 bags of cement 60kg and 4 times the cost per meter of 100UC.
This wall is engineered to have posts 4 meters into the ground and up to 2 meters above. They are cemented in 2.4 metres of concrete (if my calcs are correct 600mm x 4m).
My guess is each post would be 250 kg and ~ $800 per post, probably $4k to $5k per bay (Posts, sleepers, concrete, labour) not including drainage, rock and backfill. Big Job!
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