The hybrid rock wall, part theree.

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Farming today compared to the old way, My life my struggles, 

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Here we are trying to show you, how an hybrid rockwall can look like. Anyhow, this picture has been taken from the internet, where I could not find what I wanted, but this is how a hybrid rock wall can look like. But in the text is a differen shape.  

Welcome to our blog, DIY Retaining walls, part rhree. 

Completing the hybrid rock wall, and other things. 

So, before we build this retaining wall, we must work out how much lean against the bank we want, here we must keep in mind, how tall and how thick is the wall, we don’t want the wall to lean too much and rely only on the dirt behind it to hold it back, but at the same time we want to lean it against the bank so that the weight of the wall is used to hold the dirt back.

Here we must go back to look at what happens if you lean a monolithic object to the point it is going to fall; what happens here is that the monolithic object is going to fall, only after its centre of gravity falls outside the area of the base. Now we don’t want to go this far, and we don’t want to use the centre of gravity to decide that, but we are going to lean the wall about two third of the thickness, so that the very top layer is still vertically one third of its thickness above the base; we believe that it is very safe to go this far and the wall would stand up even if we don’t backfill it. Anyhow, in our case we are not going to backfill it, because we have cut the bank exactly as the wall is going to be, you see we are going to use the bank as a template, so, we believe that we are not going to backfill it at all.

Now that we know how much we are going to lean the wall; we are setting a leaning profile on every corner leaning approximately 10 to 12 centimetres per metre and we are ready to resume building our hybrid rock wall. But there is still another important thing to work out; we need to make sure that when it rains the water that seeps behind the wall can run out, so, we must leave a way to drain this water out and at ground level is the right place to do that, so, we choose a few spots about a meter apart and mark them, then when you lay next course of stones make sure that you leave a space between the stones that the water can run out, you must also leave the back free of abstractions for a course or two around this space, so, in this space after laying the front stone, just lay some smaller stones dry against the bank to stop the concrete blocking the drain, then you can resume to concrete the lot. Alternatively, you can lay a few short pieces of pipe across the wall for drainage, but you have still to make sure that they are clear of any obstruction at the back near the bank.  

So, now you can go back to mix some cement to lay your stones, you can mix a batch of river sand four to one that you can lay between the rocks to give them a bit of grip, you are laying the rocks in a straight line that you have tied on the profiles, when you do that make sure that this cement does not come too far forward, because you still want the rock wall to look like a rock wall, at the same time do not forget that you have to leave these spaces with no cement at all for the seepage where you have marked, after you have used the batch of river sand and cement and laid say a course of rocks, you can mix one or two batch of concrete to fill the back of the stones, then you repeat this procedure until you build the entire wall.

At the top of the wall, because the wall in not going to be level, you may have to do some adjustment to follow the height of the ground, here you have to use common sense the best way you can, if you happen to have enough wide and long rocks that can be used for a coping, use them to finish your wall, if not, just use your common sense and use anything that is available, even if it is going to be a strip of concrete in the back of the wall, so that all the wall is tied up.

I hope I have explained well enough for you to follow my way of building this hybrid rock wall. Here I want to add that this is just one way out of several other ways that can be used. A lot depends how the bank has been cut and if it follows very closely the shape of the wall, so, you can use it as if it is formwork, but if there is going to be some back filling to be done, you may have to consider some temporary formwork that can be easily removed before you backfill. All these things can vary from job to job, and if you see that it is hard to build your hybrid rock wall, then you must consider other ways to build your retaining wall.    

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Why we need these retaining walls? 

Let us explain again why we build these retaining walls. You see, when the block of land is steep, it requires a lot of work to be done, if you want a small portion of your land flat, so that you can stand and enjoy whatever is there to enjoy and do whatever you want to do in the open air.  See the photo here under, they have built a Besser block retaining wall with an indent in it, mainly to give extra strength to the block wall and to put this concrete slab and use this indent with whatever they want to do next. Note that above this block wall there is another sleeper retaining wall, these sorts of things are very costly, and we must plan it out before we start, anyhow, under below we are going to write about a Besser block retaining wall, first just a normal strong retaining wall and after that we are going to build a leaning Besser block wall, similar to the hybrid rock wall. 

There are many types of retaining walls, above is a Besser-block retaining wall, they are usually made with hollow concrete blocks, 190 x 190x 390 mm, laid with mortar 10 mm thick joint, steel reinforcement bars are placed in the hollow part of the bolock, then they are filled with concrete, once the wall is dry enough to with stand the strain. 

Building a Besser block retaining wall. 

Besser blocks retaining walls require a reinforced concrete foundation with steel starter bars placed exactly in the centre of the hollow part of the block, when you look at the wall from the front or back, and if possible, a bit close to the side where the pressure of the soil is going to be, but that can be asking too much from the concrete man and the steel fixers. So, a profile must be in place before you can even concrete the foundations, or fix the steel in the foundation, because all measurements need be known and easily measured while working on it.

This is a very demanding job and it is not a do it yourself job. So, the name that I have given this article DIY retaining wall would not apply in this case, you see I apologise because I was forced to use DIY just to overcome the problem of the title that happens when we start a new article and find that the name we have chosen has already been taken.

Anyhow, when you start laying the first Besser block in most cases, it is helpful if you can start the first course with an open block, this block looks like a square C, and you lay it with the open side facing away from the bank that it is going to hold back when everything is done, the corners are built with normal blocks and most of the walls are built with blocks that look like an H, so, it is easier to fill up with concrete, once the wall has been built. Now while the block layer is laying the blocks, he will have to lay horizontal steel bars between the courses of blocks as specified, if there is a plan and specifications, or use common sense, or copy from the specifications of a similar job he has done, the vertical steel bar will be inserted from the top before or while pouring concrete into the blocks.

Now the reason why we need to use an open C shaped block for the first course, it is because it is necessary that before we fill up the blocks we remove the mortar that has fallen down at the bottom of the blocks while we were laying them, you see, we want a solid base and we want the concrete to bind around the starter steel bars that we have laid in the foundation and this is the best way to make the retaining wall as strong as we can. Once that is done, we can fix a plank against the openings, and we are ready to pour the concrete in the wall. 

Here we must say that for this retaining wall we have not mentioned any drainage yet, so, what happen to the water that seeps behind the wall needs to be worked out, you see, sometimes when we build walls this strong, there could be a reason that we do not want any water past the wall, it can be part of a base of a house being built, so, we have not even left any weep holes in the wall, because there is going to be a drainage pipe laid behind the wall surrounded by gravel. The wall might also be treated with special paints to waterproof it.

This is one type of blocks retaining wall, and I am going to write about another type, where we lean the retaining walls towards the bank for future back fill that it is going to hold up, this is a large job that we did years ago in a yard of a new large home in Redhill a Brisbane suburb. We are going to write it here, to show you another type of retaining wall and the many ways that can be built.

 

Redhill backyard problem solved. 

Years ago, we worked on this part brick house in Redhill, we say part brick house because the top floor of the house and the interior was made of timber, so, it was a brick veneer, the base was solid bricks and blocks, it was a large house, on a large block of land had two street frontages. It was on a hill and the difference between the front and the back yard was a lot, but the two street frontages was good, because the house was being built on the higher part of the block of land, where it was nearly flat there and almost level with the road, so, there were no problem building the house; but the back yard was very steep, in some places could have been up to 45 degrees.

So, when we finished the brickwork on the house we were asked from the owner, if we could build some retaining walls, because the backyard was useless as it was. So, after discussing the financial part how he would pay us; we discussed how we could fix the back-yard building block retaining walls. So, it was agreed that we had to lay these block retaining walls leaning a few degrees towards the bank. We had to build concrete stairs on one side, so that the house could also be entered from the back street, so, working together with the owner we did the following.

Because you cannot build a very high wall on the road boundary, first a section of about 4 feet wide (1.2 m) was dug and a foundation was poured, with starter steel bars as needed and the main wall was set about a meter from the road where the first retaining wall was to be build, this was the main foundation for a start, some of the small foundations and other adjustment we had to work out as the work progressed.

The decision was that we had to build the wall leaning towards the bank for extra strength; you see, when building retaining walls the weight of the retaining wall with the weight of the foundation must be more than the weight that the backfill can move, if possible that you can build a very strong monolithic wall and foundation together this is the best solution, in this case it was not possible, because the job was too big, beside that you need to have a very wide and heavy foundation and a very strong bond between the foundation and the wall, since this bond between the foundation and the wall is the weakest point unless it is concrete and poured together, but we were using blocks to build the wall, therefore, it had this weakness at the bottom of the wall, therefore, by leaning the wall towards the bank, the weight of the wall becomes  the first point or resistance.

Now, how much we must lean the wall was left to us block layers, because for sure there will be problems, and there were several problems to overcome; the first problem is that if you have to return the corners it cannot be done, but we had corners on the boundaries of the joining block of land, so, we had to think how to overcome this drawback, for this it was decided that we would not build the corners as usual, we should treat them as separate, but we would place a corner steel rod every course, instead of every second course, as in the wall itself.

There was also the possibly that while we were building the wall, if we lean it too much it could fall on the inside, while we were building it, so, we had to strike a balance. Knowing that this first wall was going to be no more than 3 meters high, we worked out that if we lean the wall 5 centimetre per meter, the top of the wall was going to be about 15 centimetre back from the perpendicular, the blocks were 19 centimetre wide and it would be okay, as once the wall was built it could stay up on its own without falling inside, but while we were building we should be very careful not to apply any extra weight on the leaning wall, just for fear that this could happen we added a couple of block piers behind the wall, this would not only make the wall safe for us while we were building it, but it also would make the whole wall stronger. 

Anyhow, we built this block wall placed the reinforcing rods in place, we also built some concrete steps on one side of it, so, that if you happened to be on the back road you could walk to the house, the ready-mix truck came, and the wall was filled with concrete and that was the first stage finished. We had to wait for this wall to become strong before we could backfill it, and then we could build another retaining wall halfway the backyard to finish the job.

Dear readers, be warned that this type of work can only done from very experienced block layers, as it breaks all the rules in the building trade, but we did it and it worked. 

Anyhow, this article is becoming too long, so, see you in our next article, Mix your own cement. 

To see more or the entire article click on this link, DIY Retaining walls.