We see several works using the soil as part of its structure, whether they are on embankments, roads and even in dams. But what about when this soil alone does not support the loads or is unable to maintain its stability? Then get to know the reinforced soil.
What's up Engineering Lovers, my name is Igor Felipe and today we are going to talk about reinforced soil. When we talk about structures, we end up thinking quickly about concrete structures and metallic structures, but the truth is that all these structures will support another structure, which does not come to mind intuitively, the soil itself. Yes, we use the soil not only as a support structure, but also as part of the structure.
For example, if we are going to build a dam, which is a type of structure, we take into account the technical requirements and costs of its construction. If we decide to use reinforced concrete, we will greatly increase the cost of execution, and this can make the project unfeasible. That is why many of our dams here in Brazil use the soil as part of the structure of the dams.
And it is not because we are exchanging concrete for soil that the dams become more fragile. If they are designed, calculated, executed and mainly monitored as specified, they can be as reliable as reinforced concrete dams. But not only in dams, but also on our roads.
Our streets use the soil to dissipate vehicle loads. For the streets to be well built, we must control their base and sub-base very well so that we can later asphalt them. But, what if this soil does not have sufficient strength, or the geometry of the work may end up leading to its rupture?
That's where we can use reinforced soil. But what is reinforced soil? We have what we call reinforced soil, reinforced landfill or reinforced earth, when we use the soil together with another compost to improve its resistance and better distribute its tensions.
Let's explain it better. Soil is a friction material, that is, it has its connections according to the friction between its particles. What guarantees this frictional force between soil particles is what we call cohesion.
Cohesion is basically the shear strength of the soil, but not all soil has this cohesion. We have cohesive, non-cohesive soils and mixed soils. As an example of cohesive soil, we have clay, where the material is so fine that it guarantees a great bond between its particles and the voids between them are extremely small.
An example of non-cohesive soil is sand. Because their particles are thicker, they do not have a good connection between them when they are dry and ends up having a greater number of voids between their particles. Mixed soils are a mixture of the two.
In the case of sand, you can even have a good connection between your particles, you just have to wet the sand. You must have played or seen a sand castle when you went to the beach, right? The moisture present in the sand ends up guaranteeing its connection between its particles, which is why we were able to build sand castles.
And to explain about the reinforced soil, I will use exactly the sand as an example. When the sand is wet, it creates a bond between the particles and you can shape it as in the image. However, the water present in the sand can even guarantee a bond between its particles, but when we apply a load, we can cause this structure to break.
When the sand is dry, it has no force between its particles, and this causes it to collapse only with its own weight. However, if we confine the sand in a container, it can better withstand the loads on it, whether it is dry or wet. This is because once the sand is confined and we apply a load, it ends up generating internal stresses in the sand.
We call these internal stresses shear stresses. Once these stresses meet the confined container, the sand distributes these stresses on the sides, generating what we call the confinement pressure. It is this confinement pressure that guarantees a better stability of the soil and improves its resistance to shear.
But Igor, does it mean that to reinforce the soil, I have to confine it in a container? Yes, basically if you confine your soil inside a container or confine it inside the soil itself, you are already reinforcing the soil. If we are going to analyze, soils are materials that have several rupture planes.
If we analyze a rupture plane perpendicular to a load, we can say that it is being applied perpendicular to the plane, causing it to be compressed, and increase its shear strength. But if we analyze an inclined plane, the same load will decompose into two forces, one vertically and the other horizontally. This decomposition of the load will generate a result that will end up increasing the shear stress in the soil.
If this shear stress exceeds the shear strength of the soil, it will rupture. And the greater the angle of this analyzed rupture plane, the greater the shear stress. When we confine the soil, the generated confinement pressure helps to dissipate these shear stresses, causing the soil to support greater loads.
But Igor, what if I can't confine my soil? Well, if we are unable to confine our soil, we have to think of a way to control these shear stresses. Applying a load on the ground, and analyzing the same inclined rupture plane, we have the generated shear stresses.
If we use a material inside that soil horizontally, the shear stress generated in that plane, one hour you will find this material that cuts the line of rupture. This will cause this material to receive part of that tension, causing it to be pulled. If the stress on this material is greater than the shear stresses of the load, we are reinforcing the soil as if we are creating a confining pressure.
It seems difficult? If we use that same example with wet sand, put small pieces of paper in layers and compact, when we remove the glass and place a load, the paper ends up receiving part of the tensions, making the same soil support more load. On one side we have the compacted wet sand, and on the other side we have the compacted wet sand but with pieces of paper.
And just this simple example, already shows that the sand can support more load because of this reinforcement. But to reinforce the soil, do we use paper? No, and to demonstrate it better, this is reinforced soil.
We can use this type of mesh as reinforcement inside the soil to distribute the shear stresses. The soil is executed in compacted layers, and between these layers, we apply this mesh to reinforce the soil. With this, we were able to dissipate the shear stresses in each layer and thereby reinforce the soil.
A very common example where reinforced soil is used is on roads. When we need to raise the level of the road in relation to another point and we don't have enough space to create a slope, we can use the reinforced soil to create this gap. Normally, we also perform lateral closing of this reinforced soil with interlocking concrete slabs or with shotcrete only to avoid carrying material.
The reinforcement can use both the mesh that I showed in the video as well as steel meshes or steel ties, and they have the same purpose, which is to receive the shear stresses of the soil. And just as concrete is reinforced with steel, the soil can also be reinforced with other materials to improve its strength. And I will leave here, two videos that I am sure you will like too, so check out one of them.
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