Hi. I've searched quite a bit on this forum and the rest of the internet for guidance on how to reinforce a cast concrete retaining wall on solid rock. I've gotten a lot of information but am still wondering how the wall should be anchored to the rock in the best way...
I am planning to cast a retaining wall in concrete. I feel pretty confident about the wall's design and construction itself.
I have the following questions:
1. How deep should the reinforcement bars be in the rock? I read somewhere that 150mm should be sufficient.
2. How many bars should be anchored in the rock? My thought was cc200 mm on the actual reinforcement of the wall, but should each bar be anchored in the rock? That would mean about 450 holes with my 15-meter-long wall.
3. Do I need to construct the wall as an "L-support" as my sketch shows?
4. Is 10 mm reinforcement bar sufficient?
5. How many drainage holes are suitable for 15 meters?
Please see the sketch for better understanding. Thanks in advance!
I am planning to cast a retaining wall in concrete. I feel pretty confident about the wall's design and construction itself.
I have the following questions:
1. How deep should the reinforcement bars be in the rock? I read somewhere that 150mm should be sufficient.
2. How many bars should be anchored in the rock? My thought was cc200 mm on the actual reinforcement of the wall, but should each bar be anchored in the rock? That would mean about 450 holes with my 15-meter-long wall.
3. Do I need to construct the wall as an "L-support" as my sketch shows?
4. Is 10 mm reinforcement bar sufficient?
5. How many drainage holes are suitable for 15 meters?
Please see the sketch for better understanding. Thanks in advance!
These are relevant questions.
Theoretically, it doesn't look completely wrong.
But
- It is not clear what type of stone/rock it is. (test and see when you drill - do splinters fly? - does it want to crack? - ...)
It is crucial whether it is possible, realistic, or how deep you should drill.
As for the diameter of the hole, it is not as easy.
Depending on the shear force the rebar will be exposed to (i.e. what load might be in question.) determines what thickness of rebar is needed (10/12/16mm or ...)
(I see you have concluded 10mm... Personally, I feel it's a bit small - but I don't know how big the load will be)
Suppose you decide on 12mm (guessing on my part.) and you are going to cast, then the hole should be at least 24mm (maybe a bit more) to ensure the concrete really "flows down" to the bottom.
But there is another problem - How "tight" will the connection be?
Probably, an ordinary rebar will rust away over time. (the cover layer becomes too small. - In your case, it should be at least 30mm between the iron and the surrounding). Perhaps rust will "run" after the stone.
If concrete is to work, it should probably be "frost-treated" with porosity agents (but it is very difficult to do yourself) - Concrete stations use meters during mixing.
What would happen if you instead use hot-dip galvanized expansion bolts? stainless threaded rod? (but it is not as "tough" in nature)
Instead of fastening with concrete - look at anchor mass? (the hole does not need to be as wide)
I leave the dimensioning unanswered.
When I look at your sketch, the construction will likely become quite heavy - the base is sloping, and backfill behind (pressing on)
Spontaneously, the "lip" pointing backward feels too small.
It also seems like you will get both a pushing moment and a twisting moment that these "pins" in the ground have to handle. (then even thicker anchoring is required)
I would consider mounting "lifting rings" into the stone a bit above/behind the concrete angle..
using stainless steel cable between the ring and high up in the concrete angle to counteract the "twisting".
(these will be hidden under the refill masses)
It would also "pull" the concrete angle slightly downward, further reducing the need for "super strong" dowels.
I would probably also tilt the front of the concrete angle a bit "backward" to further reduce the twisting force.
The alternatives are quite many, but the basic rule is
- Ensure to stop the twisting on the concrete angle.
- Prevent the stone from sliding downwards.
(I am not an expert in the field
)
Theoretically, it doesn't look completely wrong.
But
- It is not clear what type of stone/rock it is. (test and see when you drill - do splinters fly? - does it want to crack? - ...)
It is crucial whether it is possible, realistic, or how deep you should drill.
As for the diameter of the hole, it is not as easy.
Depending on the shear force the rebar will be exposed to (i.e. what load might be in question.) determines what thickness of rebar is needed (10/12/16mm or ...)
(I see you have concluded 10mm... Personally, I feel it's a bit small - but I don't know how big the load will be)
Suppose you decide on 12mm (guessing on my part.) and you are going to cast, then the hole should be at least 24mm (maybe a bit more) to ensure the concrete really "flows down" to the bottom.
But there is another problem - How "tight" will the connection be?
Probably, an ordinary rebar will rust away over time. (the cover layer becomes too small. - In your case, it should be at least 30mm between the iron and the surrounding). Perhaps rust will "run" after the stone.
If concrete is to work, it should probably be "frost-treated" with porosity agents (but it is very difficult to do yourself) - Concrete stations use meters during mixing.
What would happen if you instead use hot-dip galvanized expansion bolts? stainless threaded rod? (but it is not as "tough" in nature)
Instead of fastening with concrete - look at anchor mass? (the hole does not need to be as wide)
I leave the dimensioning unanswered.
When I look at your sketch, the construction will likely become quite heavy - the base is sloping, and backfill behind (pressing on)
Spontaneously, the "lip" pointing backward feels too small.
It also seems like you will get both a pushing moment and a twisting moment that these "pins" in the ground have to handle. (then even thicker anchoring is required)
I would consider mounting "lifting rings" into the stone a bit above/behind the concrete angle..
using stainless steel cable between the ring and high up in the concrete angle to counteract the "twisting".
(these will be hidden under the refill masses)
It would also "pull" the concrete angle slightly downward, further reducing the need for "super strong" dowels.
I would probably also tilt the front of the concrete angle a bit "backward" to further reduce the twisting force.
The alternatives are quite many, but the basic rule is
- Ensure to stop the twisting on the concrete angle.
- Prevent the stone from sliding downwards.
(I am not an expert in the field
)