Sunday, June 7, 2015

Building the hybrid rock wall

Welcome to our blog, Menfranco general blog
and this post, building the hybrid rock wall
Building the hybrid rock wall
The hybrid stone wall that we are building can look like this wall here, if built properly

Building the hybrid rock wall  
Dear readers, as we have said in our previous post, in this post we are going to describe how to build a hybrid rock wall. Now, this hybrid rock wall that we are going to build is really a big job if you are going to do it yourself and you are not a tradesman, however it can be done if you follow the way that we are going to describe here under.
So let us repeat briefly what we had done before, so that it is easier to follow our next move; as you know we have dug in the yard because we needed some room and now we are left with a bank in the backyard that needs to be held back from a retaining wall. This retaining wall that we are building will starts at ground level at its lowest point, as we have dug the ground approximately level, and then follow the natural ground, because we are building the wall only to the height of the natural ground level, it is going to start from almost nothing and at the highest point will be 1.8 meter, it is really two walls that meet and forms a square angle at the highest point.
Here we have to say that this retaining wall that we are building, some people might think that this cannot or should not be done, as this is neither a rock wall nor a concrete masonry wall, as it mixes about everything, but so what, if it is convenient, why not do it? I have to say that in my life time I have built walls like this with whatever was available on the site; and I mean everything in fact I was using stones that were laying in this small creek bed and pieces of concrete that we had broken to do some alterations and old bricks, some concrete and some mortar, this has happened a few year ago and last time I have seen the owner he said that the wall is still there. So, most things can be done as long as you know that it has got a good chance to last a long time.
 Let us go back to build our hybrid rock wall, first of all to build this wall you need a few cubic meter of rocks, because you want the wall to look as a rock wall, you don’t need very big rocks or special size rocks, because you can use the cement wherever necessary to fill the gaps and this might be good, as the rocks could be less expansive, you need a mixer, you need some gravel, sand and cement; and of course you should have the tools to do the job.
You got all this on site and you can start to build. First of all drive a couple of pegs in the ground, exactly where you wand the face of the wall to be, tie and stretch a line on these pegs and see any adjustment that you need to do before you start laying the first stone. What you are looking for here is that the bank you are going to build the wall against has been dug straight, it is almost vertical or just a few degrees sloping, you have also dug a shallow foundation as you want the wall to be strong enough to last for a long time, so you are satisfied that the foundation is going to be solid enough, since it is well below the original natural ground, and therefore can hold a lot of weight and pressure, even though you have dug it out one side, the ground is very compact. 
You have done all that you have set the pegs again so that your wall is set to be about 10” thick overall, you have chosen this thickness because most of the large rocks seem to be that thick, so now you are ready to lay the first course of stones, mix a few batches of concrete and lay it in the foundation and then before this concrete sets lay the first course of stones on this concrete making sure that the bottom of the stones are below ground level, so that the entire stone wall seems to start from below the ground; once you have done that you can fill the back of the stone with concrete a bit above ground level but below the full height of the stones, because you want to leave enough room to lay next course of stone easily. Now the wall is all set to go, but we need to reset how we have to continue and complete the hybrid rock wall, the right way with the right lean against the bank, yes you heard it right the wall is not going to be plumb, it is going to lean. You need to lean the wall against the bank, so that the weight of your wall by itself adds strength to the wall.
Completing the hybrid rock wall
What we need to do now: first of all we are going to set up how much lean against the bank we want, before we build this retaining wall, here we have to keep in mind a few things before we definitely decide that; first of all we have to consider 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 one has to go back to look at what happens if you leans a certain 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 for a few reasons, 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 only 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 anything, 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; you see we need to make sure that when it rains the water that seeps behind the wall can run out, so we have to leave a way to drain this water out and at this 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 also have to leave the back free of any 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 could 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 just common sense the best way you can finish, 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 would like 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 that 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 this things can vary from job to job, and if you see that it would be hard to build your hybrid rock wall, then you have to consider other ways to build your retaining wall.
Of course there are several more ways of building retaining walls, some of which we are talking about in our next post, as this post again is becoming too long, and also what we are going to write next is a bit different from what we have written now. So see you next time, in these retaining walls.     

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Menfranco general blog, 
Building the hybrid rock wall
Next time with, these retaining walls
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