Pile foundation with grillage: step by step instructions

The article will consider a pile foundation with a grillage. It is not always possible to apply traditional designs - slab or tape. Sometimes they become too expensive, only the foundation will take up to 50% of the total budget. As a rule, a pile foundation of this type is used in cases where there is construction in an area where the depth of freezing of the soil is more than two meters. Often, such foundations are built on weakly and unstable types of soils.

Foundation design features

What is the foundation on stilts? Everyone knows this - this is a certain number of poles that are clogged into the ground. Moreover, the lower edge is at a depth of soil freezing. But such a design in its pure form is rarely used in practice.

The reason is that it is quite difficult to distribute the load that the house creates on all piles. One will be heavier, and the other less. It is for this reason that pile foundations are used, as a rule, in structures with low weight - under logs from timber or logs, frame houses.

Bars or logs have one good quality - they allow you to redistribute the load evenly to all points of support. Buildings from other materials can do this much worse. But the device of the pile foundation with grillage is such that it does not have the drawbacks indicated above. Therefore, it can be used without problems in structures made of brick or block. The structure consists of several piles and a tape (usually made of pure concrete or using metal reinforcement), which connects all the support points. It is this tape that is called grillage.

Features grillage

The grillage is part of the foundation, which combines the upper parts of the piles. It takes all the load that the structure creates, and due to its closed-type device, it evenly redistributes it to all piles. The grillage is of the following types:

1. Concrete.
2. Reinforced concrete.
3. Metal.
4. Wooden.

Reinforced concrete and concrete can also be divided into two subcategories - high and low.

The first are located significantly above the level of the earth's surface. Very often grillages are made of metal - square metal pipes, channels with a large cross section are used. But the device of concrete grillage is much more complicated.

Features grillage

As you understand, the house gives a different load on the premises. Indeed, in it furniture, decoration, various appliances and things are distributed unevenly. Of course, the load on the supports will also be different. Using the grillage, it turns out to convert all the loads so that the piles installed under it are affected by the same forces. This quality is very useful, as it allows to achieve stability of the entire structure.

If the piles are loaded evenly, then the likelihood that they will shrink differently is reduced. If the foundation sits unevenly, then cracks will appear on it and the walls. The device of the pile-grillage foundation is highly stable. But still, the construction did not get rid of the main drawback of the piles - it is not known what type of soil is near them.

Should I use piles?

Architects do not really trust the designs based on piles - it is almost impossible to predict their behavior in the ground in advance. Near one pile, the soil will be dense, and next to two adjacent ones it will be loose. And there will be uneven shrinkage of the whole house.

But there are more predictable designs, which we will talk about later. In particular, this is a pile-screw foundation with a grillage, which is characterized by high strength. But its cost is quite high.

Strip foundations on stilts

Low types of grillages are good because their behavior can be predicted. This type of grillage begins well below ground level. And they are made of simple concrete or reinforced. It should be noted that the reinforcement emerging from the piles is connected mechanically with the reinforcement of the grillage itself. It is also worth noting that the warming of the grillage of the pile foundation is carried out in the same way as the tape. The materials used are the same. The designs are very similar.

We have a grillage as a tape foundation of a shallow type. Its manufacture is made by the same technology. And the difference is that in addition there is a connection with piles, which significantly increase the stability and reliability of the entire structure. Foundations of this type are called pile-tape or tape on piles. Without exaggeration, they are considered ideal, since they combine all the advantages of both types of foundations, and the disadvantages are compensated.

Foundation work

The work is as follows. All the load that a house creates affects a concrete tape. Since there is longitudinal reinforcement, forces are distributed evenly over the entire area of ​​the support. Partially the load goes into the ground, the rest take piles. And one feature should be noted - shrinkage and load are uniform, since these parameters are aligned using the tape. It is desirable that a pile foundation with a grillage be installed to the freezing depth.

In winter, heaving forces act on the foundation - at this moment you can see all the advantages of the tape structure on piles. When the heaving soil acts on the construction tape, the piles do not allow the foundation to move. In this case, the likelihood of skewing the building is reduced. You can get rid of the effects of heaving soils if the foundation is poured below the freezing point. But the cost of this design is quite large, it is not recommended to use it.

In what cases can pile-grillage foundations be used

And now let's talk about in which cases the use of foundations of such a design is simply necessary:

1. In cases where weakly and unstable soils go to great depths. As a rule, these are soils of karst, peat, forest types, as well as plant, quicksand, fertile soils with a thickness of more than one and a half meters. The load must be transferred to the soil more dense, which is much lower. As you know, digging a trench and reaching the ground with high bearing capacity is quite difficult. And the construction of the foundation will be quite expensive - therefore, the use of piles is the way out.
2. During construction on a site where a large difference in elevation is observed. When constructing the foundation, it turns out to be easier to use piles with different heights than to level the surface or fill the tape at great depths in order to slightly compensate for irregularities.
3. If groundwater is located too high. In this case, only the height of the grillage of the pile foundation is important. It should be noted that during the construction of the pile foundation it does not matter at what depth the waters are located. The main thing is that under the so-called heel is located the soil, which has a high bearing capacity. The level at which groundwater is located can only affect the type of grillage. If the water is close to the surface, you need to make a high grillage. And if the water is deep, it is allowed to make a low design.
4. If a building is being built on hard ground. When constructing a strip or slab foundation, it is necessary to do a large amount of earthwork. In this case, the use of piles is justified.
5. When building frame houses, it makes no sense to build a strip foundation - it's just a waste of money. The margin of safety is unreasonably high, it is best to choose a pile-grillage design.
6. If the total mass of the structure is more than 350 tons, it is best to erect a pile foundation with a grillage. Tape or slab structures will be too massive, and even expensive.

It is still worth noting that the most reliable types of foundations are tape and slab. But if there is no means to erect such a complex structure, and a large margin of safety is not required, it is allowed to use a pile-grillage type.

What are the piles?

As a rule, absolutely all types of piles are used in construction. When choosing, you need to pay attention only to the type of soil and the maximum permissible load that the building creates. Piles can be made of concrete or metal, they are rarely made of wood. The cross section is either square or round. It is necessary to make reinforcement of the grillage of the pile foundation, so that the whole structure is as strong as possible.

You can distinguish these types of piles by type of installation:

1. Driven - mounted without using excavation or drilling. They are driven into the ground using special equipment. For this reason, they are rarely used in private construction.
2. Bored - in the ground it is necessary to make a well in which the formwork is placed. After its fastening, reinforcement is mounted (it increases the strength of the structure. After the performed actions, concrete is poured inside.
3. Reinforced concrete drilling - as in the previous case, you must first make a well. Then the ready-made piles are driven into it. Efforts for this need much less than when installing driven ones.
4. Screw - somewhat similar to self-tapping screws. They are made of metal, the ends are pointed and there are blades. With their help, the soil is cut. If it is necessary to install piles to a greater depth, you can not do without special equipment. But when installed to a depth of three meters, you can do without it.

In the construction of private houses, bored piles are most often used. But, as a rule, they are installed as supports for small buildings - sheds, baths, etc.

Pile Forms

Piles differ in sectional shape:

1. Round.
2. Square.
3. Triangular.
4. Hollow round.

Often more complex forms are developed, it all depends on the specific project.

Ground load distribution

It should be noted that pile foundations with a monolithic grillage are the most durable and strong. But, as you know, piles can distribute different loads on the ground. There are such types:

1. Pile racks.
2. Hanging.

The latter have a rather large lateral surface. It is with its help that they transfer the lion's share of the load to the ground (about 70%). Such constructions are used in those cases when it is not advisable to go deeper, and the level achieved is not enough to withstand the entire load. The design has a heel, but its presence does not change the picture - all the load goes to the ground not through the tip, but through the side surface.

But the piles of the rack transfer the load through the tip. The walls are smooth and undeveloped, but at the end the heel is made - an extension that allows you to increase the area of ​​the support. Thanks to such a support, the heaving forces cannot lift the entire foundation. But in order for the support to be of high quality, it is necessary to calculate the grillage of the pile foundation. Entrust this procedure is better for experienced professionals.

How are the piles in the grillage

As a rule, piles are located in the soil strictly vertically, but in some cases they are mounted and inclined. Moreover, it is allowed to install several piles in one place. This method of construction is used in cases where there is a likelihood of horizontal forces. A good example is if construction takes place on a slope site.

Pile arrangement under the supports is also allowed. This is typical when erecting canopies or building a roof over an open area. Piles are installed under the columns that hold the roof.

When constructing a private house with a small number of storeys, piles can be arranged as a tape. They are set in a row, and sometimes in two or three. Often in places where it is planned to have a large load on the ground, several piles are located at a small distance from each other.