GENERAL CONSIDERATIONS ABOUT HOW TO BUILD A WALL
The retaining walls must have the characteristic of being so resistant to withstand the pressure of the ground. There are many factors to be kept into consideration when building a retaining wall, whether you are building a wall with the purpose to prevent a steep terrain from collapsing or if your wall must support the weight of a standing vehicle or a land on wich you will rise a building.
For centuries retaining walls have been built mostly using stones, ‘dry’ or with various kind of ligands, such as clay, mud, lime, mixed straw and earth cooked or raw and, in more recently, using concrete.
It is impressive to see how ancient buildings have been able to overcome the centuries and are still standing under our eyes, often in very good conditions. The key that enabled to obtain these results, among others, is to take in due consideration the experience gained from the mistakes and breakdowns, in order to achieve more and more expertise.
That was to be said, and so we now go through the matter….
Among the factors to be taken in due account and with which we must deal during the project and the construction works, in addition to the force of gravity, which is a common element to all walls, there are the characteristics of the weather, wet, dry or cold. Yes, the weather, this factor could often determine a successful work or a delay or even a poor job if you do not keep well in mind his importance.
The ground we want to support, always tends to push towards the center of the Earth, even though there are other forces that exert a strong side pressure. Therefore when you are planning to build a wall, it is recommended do not underestimate the strength of the thrust of the ground: usually 40 cubic feet of soil weight about 503 lbs to which it must be added the additional percentage of water absorption.
Higher the retaining wall is and greater is the chance to collapse. If the height of a wall is doubled, the exerted force is tripled or even quadrupled.
Another useful suggestion is to make an inspection over the vicinity of the site where you are planning to build your wall, in order to verify which constructions techniques are used and what kind of materials were used, as well the level of conservation of the neighborhood walls. This may help you with the choice of the materials to minimize the risk factors.
If possible, try to limit the height of the wall keeping it under the five feet mark, in fact if it exceed this height it would be convenient to tilt the wall toward the soil so the CG is back and hence increase the strength and resistance level.
A terrain subject to freezing expands its volume by exerting greater pressure against the wall and it is possible that rivulets of freezed water can lead to breakdowns. Keep always in mind that the ground freezes from the top exerting a greater pressure in the upper part of the wall.
A good solution to minimize the problem it could be mixing soil with porous and light material and at the same time, make several outlets on the wall for the water could have accumulated behind the wall.
A retaining wall can be constructed of various materials:
- reinforced concrete
- concrete blocks (called Plo),
- cut stones
- irregular stones
- bricks, etc
Crucial to ensure an adequate seal is the construction of appropriate foundations with reinforced concrete which must be thickness for not less than twice the thickness of the wall and deep at least 1/3 of the height of the wall above ground.
FOUNDATION OF A WALL
Very important is the foundation of the retaining wall. Keep into due consideration that the excavation must be broad enough to allow you to work properly so to build around a formwork plank of wood nailed together with nails (remember do not push completely the nails to easily remove them). Really, the formwork for the foundations could also be avoided for walls not too high, you can start building the wall directly from the bottom of the excavation.
The excavation for the foundation of a wall must be at least 15-20 inches deep and into the above mentioned formwork made of smooth wooden boards, we must pour a first concrete casting, (1 part cement, 3 parts sand, 5 of gravel and 3 of water) by create a layer of approximately 3-5 inches, then pour the concrete and …drown in it an iron cage that consist of 4 longitudinal iron rods ’16 inch of diameter and 6 brackets interaxis placed at 10 inches from each other tied together with steel wire.
Then it should be allowed to dry for few days before start building the wall over, protecting it from weather with a plastic cover.
THE WALL CONSTRUCTION
If the wall that we are planning to build will be made of reinforced concrete, it is necessary that from the surface of the foundations protrude the iron rod bent like a hook to consent to bind other rebar so to reinforce the wall that will be build with the same way of the foundations, always having in mind that the cage must be embedded into the concrete for at least 2 inches from the surface in order to avoid breaking due to the difference of temperature of expansion of the two materials (iron and concrete).
It then fills the mold using a casting of concrete (1 part cement, 2 part of sand, 4 of gravel and water as needed). The cast must be done every 10 to 15 inches intervals. The previous layers to dry.
If the wall is made of bricks, then you do not need other than proceed with laying of the bricks using cement mortar and sand and cement (a little addition of lime can make it more workable dough).
THE WALL COVERAGE
The cover of the wall is intended to protect the wall and drain the rain, avoiding that the water dunk the structure of wall making it brittle.
The coverage can be built of mortar, concrete or bricks and must protrude slightly from the section of the wall.
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