Combined foundation - options and some schemes. Pile foundation with grillage: do-it-yourself device Foundation type: pile foundation

I’ve been wanting to ask this question for a long time because it’s a very popular topic.
We will accept that “pile” is a “pile grillage” distorted in the mind
Thanks to Mr. Yakovlev’s book and TISE, it has become customary to say that “de facto” it should be hanging. Everything is more or less clear with it; the air gap protects against soil heaving.
In the literature there are 3 types of grillage.
1) recessed
2) not buried
3) hanging
Moreover, I did not find a more or less clear description of what is what and what it is used for.
With p3 everything is clear - there is a lot of information on the forum.
With point 1, not everything is clear, except that the grillage seems to be buried almost to the freezing depth and is used in “large” construction. In general, this view is not very interesting.
But at the moment I am most interested in option 2. Since it is often called “pile strip” and is done by some builders.
Dear ALEX2626, in response to my statement, he described the following design - “pile strip foundation”
What do you think we should call it, if not pile-and-tape, and what does the inflamed brain of the builders have to do with it? Pile-tape (or pile-grillage) yield in almost any soil, provided the conditions are met, is simply cheaper. For example, the most common type shallow foundation- tapes - 300 mm in the ground, 500 above the ground, width 400 mm - cross-sectional area = 0.32 m2, multiplying by for 10 * 12 m - tape length 64 m, TOTAL VOLUME OF THE FOUNDATION = 20.48 M3, in this case it is necessary to Be sure to put 300-400 mm of sand and crushed stone with a tape, therefore dig to a depth of 600-700 mm, which is 18 m3 of excavation work. Now we consider the pile-tape - we drill with a gas drill (or a hand drill with attachments) to the freezing depth (in Samara 1.6 m) in one day 42 holes, put a 100 MM ASG directly on the ground and make a 500 * 400 mm tape along it, volume foundation = piles 3.3 m3 + tape 12.8 m3 = 16.1 m3 - in total we get a foundation built according to all standards, i.e. to the freezing depth at lower costs
This is exactly how it is often done on any soil citing the fact that the pillars are below the freezing depth and that means everything is ok. I believe that such a design is safe only on non-heaving soils - for the following reason:
When water freezes, it expands and, accordingly, the volume of soil saturated with water increases. Roughly speaking, the earth, expanding, presses on the foundation from below.
If you just have columns, then they are subject to lateral adhesion to the soil and pressure from below - if the column is higher than the freezing depth.
In the case of “pile strip” according to version ALEX2626, adding 10 cm of ASG “directly on the ground” will not stop the forces of frost heaving. It turns out that when the soil freezes, the expanding soil will put pressure not only on the posts, but also on this “ribbon” and the fact that the posts are below the freezing level is not at all important here.
Since the tape is rigidly connected to the piles, this entire structure will begin to squeeze out. And the most unpleasant thing here is the following - when extruded, the piles will rise in their “holes” and a void will form between the bottom of the hole and the bottom of the pile. Soil from the walls can easily fall into this void, or many other unpleasant things can happen.
As a result, the void will be filled, and in the spring, when the soil “removes”
The pile may not return to its place, remaining “raised”, and since it is rigidly connected to the “tape”, it will warp the tape.
Accordingly, this is a direct path to potential problems with such a foundation on heaving soils.
I specifically highlighted the word potential - because this is one, but probable, path of events. Moreover, this may not happen immediately, but let’s say after 2 years or 5 years or 10. Or maybe it will “carry away”...
It’s just not clear why play such roulette when you can do it differently
So I would like to understand what a “pile strip foundation” without an air gap is and how much it has the right to live in heaving soils.
Note al185. Topic summary

It is not always possible and not in all situations to use traditional foundations, including slab foundations. In some situations, they become too expensive: their arrangement can take up to 40-50% of the cost of the entire building. This usually happens during construction in areas with a large freezing depth (below 2 meters) or on unstable, weak-bearing soils. In such cases, a pile-grillage foundation is often the best solution.

What is a pile-grillage foundation

Pile foundation Everyone probably imagines: these are a number of piles buried in the ground to the level of the load-bearing layer or below the freezing level. IN pure form this type of foundation is rarely used. This is due to the peculiar design, which does not allow the load from the house to be redistributed between the piles. Therefore, pile foundations are mainly made for log buildings made of logs or timber, and sometimes for frame buildings. These types of building materials, due to their characteristics, themselves redistribute the load. They are not compatible with houses made of other materials.

But their improved form - a pile foundation with a grillage - is free of many disadvantages and can be used for both brick and block buildings. In them, all supports are tied using a tape made of metal or reinforced concrete (concrete) into a single structure. This tape is called a grillage.

A grillage is a part of the foundation that connects the pile heads and serves as a support for the walls. It is the grillage that receives and, due to the closed structure, redistributes the load, transferring it to the piles. It can be metal, wood, concrete or reinforced concrete. According to the type of execution, concrete (reinforced concrete) grillages are low and high.

The high grillage is above ground level. Most often it is made of metal - large-section channels or square metal pipes. They also make such a grillage out of concrete, but its design is more complicated: you have to figure out how to fill the tape at a distance from the ground.

How does a grillage work and what does it give?

Any house in different parts will give different loads: decoration, furniture, sanitaryware, other things are placed unevenly. Consequently, the load from its different parts will be different. The grillage takes on these uneven loads and redistributes them. The “leveled” load is already transferred to the piles.

What is the difference between pile and pile-grillage foundations (to enlarge the size of the picture, right-click on it)

Why is this good? The fact is that with the same load on the piles, there is less chance that they will settle unevenly. And uneven shrinkage leads, as is known, to cracks in the foundation and walls. Therefore, a pile-grillage foundation is more stable. Although the main disadvantage of pile foundations remains: we cannot know what kind of soil is under each of the piles. Therefore, it is unrealistic to predict their behavior. That is why architects are not very fond of them: it is impossible to guarantee long-term operation of the house.

Strip foundation on piles

Low grillages are more predictable in this regard. They usually start below ground level and are cast from reinforced (or not - depends on the project) concrete. Moreover, the reinforcement of the piles is connected to the reinforcement of the grillage.

In this case, the grillage is a shallowly buried strip foundation and it is made using the same technology. It differs in that it has a rigid connection with the piles, which significantly increases the reliability and stability of the structure. Such foundations are also called strip foundations on piles or pile-strip foundations. This design is almost ideal: it combines the advantages of pile and strip foundations, largely compensating for their disadvantages.

Construction of a pile-strip foundation (to increase the size of the picture, right-click on it)

How does it work? The load from the house is transferred to the belt. Thanks to the availability longitudinal reinforcement redistributed over the entire area. Since the tape also rests on the ground, part of the load is transferred to it, the rest falls on the piles. In this case, the load and shrinkage are uniform: they are “evened out” by the tape.

IN winter time, when heaving forces begin to influence the foundation, all the advantages of a pile-strip foundation appear. If the house is located on heaving soils, their depth is below the freezing level, it is very difficult to imagine conditions under which the house will warp or it will shrink unevenly.

When heaving forces act on the tape, the “heels” of the piles, and they themselves, do not allow the soil to move the foundation. Therefore, strip-pile foundations are an excellent choice on highly heaving soils. The costs are much higher than when constructing a conventional pile foundation, but much lower than when constructing a strip below the freezing depth.

When can it be used

Sometimes it’s even simpler: they start from the lowest cost. But you should always remember that any type of pile foundation is less reliable than slab and strip foundations. And all because we cannot know exactly what kind of soil is under each of the piles. That is why, when calculating parameters, an increased safety margin is included in the design. Not 1.2, as is usually believed, but 1.4. And still, no one can guarantee anything.

Which piles to use

Any piles can be used in pile-grillage foundations. They are selected based on the soil and the planned load of the house. Piles are made of metal, concrete, and sometimes wood. Can they be round or square section. They also differ in the installation method:

In private construction, bored piles are most often used. They are especially popular in the construction of summer houses or baths. Can also be used in construction small houses. But if cottages and baths can be built without calculations, then when building a house it is very advisable to order a project.

Different piles come in different shapes: square or triangular, round filled and round hollow, sometimes complex shapes are developed specifically for the project. Based on how piles transfer load to the ground, they are:

Hanging piles have a large lateral surface and a significant part of the load (up to 60-70%) is transferred with its help. They are used if the bearing capacity of the soil at the achieved level is not enough to withstand the entire load, and further deepening is impractical. In this case, the presence of a “heel” changes almost nothing: the main load is transmitted by the surface, and not by the tip of the pile.

Rack piles, on the contrary, transfer most of the load through the tip. In this case, the side walls are undeveloped and smooth, and it makes sense to expand at the end of the pile. One of the types of this type is . They have a cylindrical extension at the bottom, which is why they transfer the load over a large area. Also, the heel prevents heaving forces from lifting the foundation.

Location of piles in the grillage

In most cases, supports in the ground are placed vertically. Sometimes an inclined installation may be required, and several pieces in one place. This method is used if horizontally directed forces may arise. For example, during construction on sloping areas.

Piles can be located pointwise - under supports (columns, racks). This arrangement is typical when building canopies or installing roofs over open areas. Then the supports are placed exactly under the columns holding the roof.

For private houses with a small number of floors, the piles are placed in the form of a strip. They are placed in one row, sometimes in two or three, shifting them relative to each other. Sometimes in the most loaded parts, for example, in corners, under areas with a large planned load, they are placed in bushes: several pieces at a short distance from each other.

How to arrange a house plan yourself

When designing a pile foundation on your own, you usually proceed as follows. On a building plan drawn to scale, piles must be laid in the corners and at the intersections with the walls. If they are more than 3 meters apart from each other, place between them intermediate supports. It is advisable that the piles be located one from another at a distance of 2 to 3 meters.

The principle is simple, but still needs to be defined required area piles And it needs to be calculated (or rather, selected).

Calculation of pile-grillage foundation

In order to be at least partially confident in the reliability of the foundation, it is advisable to at least approximately calculate it. To do this, you will need to do several not very complex calculations.

The weight of the house is calculated (all materials and the approximate weight of the “filling” are taken into account).
Based on the weight and safety factor, the required supporting area is determined.
Since the piles have already been placed, we can count their number.
Next we select the cross-sectional area of the piles. Since we know their number, multiplying by the selected area, we find out the total.
We compare the obtained result with the reference area calculated earlier (point 4).
If the area found in step 4 is larger than that calculated in step 2, the selected pile parameters are suitable for us.
If it is less, we increase the planned cross-section of the piles, multiply again and compare. This is how we find the required area of the pile.

Sometimes it is more profitable not to increase the area of piles, but to install them more often. The calculation method does not change.

Load-bearing capacity of piles of different diameters in different soils (to increase the size of the picture, right-click on it)

The support area required for normal load distribution is calculated by the formula:

Where N is the bearing capacity of the soil (it can be taken from the table). Factor 1.4 applied because of that that pile foundations require a larger margin of safety: we don’t know what kind of soil is under all the piles. Therefore, it is better to play it safe.

For more information on calculating the supporting area and calculating the mass of the house, watch the video.

Construction technology

So, you have a project ready, or you yourself have decided on the location of the piles, their parameters, the type and height of the grillage. Construction can begin.

Marking

First, the entire fertile layer of soil is removed, taken out to the garden or stored in one of the corners of the site. The area for the foundation is leveled. Then, using pegs and cords, the boundaries of the house are marked. Moreover, two cords are pulled, marking the outer and inner surfaces of the walls. Be sure to check the geometry by re-measuring and comparing all the diagonals in pairs.

After the marking is completed, you can mark the installation locations of the piles. We have them drawn on the plan and calculated, the distances between them are determined.

Schematic representation of the work procedure when constructing a pile-grillage foundation with your own hands (to enlarge the size of the picture, click on it with the right mouse button)

Excavation and pouring of piles

How exactly the work will take place depends on the type of piles used. Most often, screw or bored piles are used when building a house.

Screws can be screwed in by hand. When twisting, their heads are aligned at the same level. It is more convenient to mark it with cords.

Drilling will require either special equipment or hand drill suitable diameter. These devices drill holes in the right places. The selected formwork is lowered into the finished wells, and reinforcement is installed (four bars of ribbed reinforcement connected to each other). If the foundation is pile-strip, then the reinforcement must have an outlet of at least 60-70 cm. It will then be connected to the grillage. The last step in this stage is pouring the concrete.

The pile foundation is ready for installation of formwork for the grillage. In this case, formwork made of roofing felt or roofing felt, rolled several times, is used.

Grillage arrangement

If a metal grillage is chosen, it is welded to the pile heads. When working, it is important to maintain strict horizontality: then the load will be transferred evenly.

To install a recessed reinforced concrete grillage (low), you will need to add crushed stone of a fraction of 20-60 mm and compact it with a vibrating platform. The minimum layer of crushed stone is 15 cm. To improve the bearing capacity of the soil under the belt, it is necessary to pour crushed stone in small layers (5 cm each) and thoroughly compact it with a vibrating platform. It will not be possible to compact well around the piles, but this is not so important.

Formwork is installed on this bedding. The width of the tape is slightly larger than the width of the walls, the height of the panels is made taking into account the required height of the base. Assembling the panels and installing stops exactly repeats the installation technology

Reinforcement is carried out in most cases in the same way as during the construction of a belt: two belts at the top and bottom made of ribbed reinforcement, transverse and vertical posts made of a smooth rod of smaller diameter. All reinforcement rules are preserved. Only the dressing with piles is added. The outlets of the reinforcement from the piles are bent: one row is tied to the lower belt, the second - to the top (do not forget to make the outlets of different lengths). They must be at least 50 bar diameters (if 12 mm reinforcement is used, you need to bend 600 mm (50 * 12 mm)). The reinforcement diagram for the pile abutment is shown in the figure.

Installation of embedded parts

At this stage, it is necessary to leave ventilation ducts and lay pipes and ducts through which they will be supplied engineering communications(plumbing, heating, electricity, sewerage).

If this is not done, you will have to subsequently chisel the concrete. And this is a great evil for the foundation, because the integrity of the monolith is violated. So think through everything carefully: there will be no opportunity to redo it.

Pouring concrete

Concrete is not just poured. It is also vibrated. Without this process, it is very difficult to achieve uniformity and high strength. Therefore, processing foundation concrete with a vibrator can be considered a mandatory process.

If the air temperature after pouring concrete is around +20°C, then the formwork can be removed after four days. During this time, the concrete will gain approximately 50% of its design strength, which is enough to carry out the following work. If the temperature was around +10°, you will have to wait 10-14 days. At lower temperatures, conditions are considered wintry and the poured concrete requires insulation or heating.

Everything is ready for pouring concrete: the reinforced belt is tied, the formwork is set and secured (to enlarge the size of the picture, right-click on it)

For all their attractiveness, pile foundations have disadvantages:

As already mentioned, due to the fact that it is impossible to determine what kind of soil is located under each of the piles, its behavior is almost impossible to predict.
In such buildings it is impossible to install basements.
With high grillages, it is necessary to somehow close the gap: animals and insects like to live there.

Domestic builders of private houses usually prefer to make a monolithic strip foundation. But for large soil freezing depths, this option is expensive. After all, he is in similar situation it has to be laid very deep, and this is an additional significant cost for reinforced concrete. In order to reduce the cost of constructing the foundation of a cottage, private developers are now increasingly beginning to give preference to a pile grillage foundation, the deepening of the support piles of which is much cheaper.

What is a pile foundation with a grillage?

Structurally, a pile-grillage foundation is a series of supports immersed in the ground below the freezing point, and connecting them on top with a “bracing” of steel or reinforced concrete. The first rows of bricks or timber (logs) are already laid on the latter. This design ensures uniform redistribution of loads from both the house and the ground.

Foundation diagram

The point impacts from the piles that arise during heaving disperse throughout the grillage strip of such a foundation. The walls do not experience excess pressure at any one point. Distortions and destruction of masonry on such a foundation are practically excluded.

Types of foundation on piles

The grillage of this type of pile foundation is made of monolithic reinforced concrete or steel channel. The most commonly used concrete structure with reinforcement. It can withstand significant loads. The option with metal piping is more intended for light buildings (garages, outbuildings, buildings made of SIP panels and bathhouses).

Pile foundation with metal frame

Pile foundation with monolithic piping

Depending on the type of supports used, the pile-grillage foundation comes in two varieties:

Screw.

Bored.

In the first case, it is an almost complete copy of the foundation on screw piles. Only on the supports is a more powerful monolithic grillage. At the same time, steel “screws” for such a design have to be chosen that are stronger, with larger wall thickness and diameter.

Those who are going to make the foundation with their own hands often prefer to use bored piles in permanent formwork in the form of asbestos-cement pipes. This technology is simpler and cheaper when done independently.

Advantages and Disadvantages

Piles in question supporting structure due to the large immersion depth, they provide excellent stability to the entire mini strip foundation on top. And they cost much less than a reinforced concrete monolith of the same height. And if support pillars tie the top not with a concrete tape, but with a metal grillage, then you can save a little more. This option is one of the most inexpensive ways creating a support for a private house.

This foundation has the following advantages:

Possibility of arrangement on slopes and in marshy areas;

Relatively cheap construction of a pile grillage structure;

Minimum time spent on foundation construction;

No need to use lifting vehicles;

Simplicity of the technology for installing bored and screw supports, as well as pouring concrete;

Excellent stability indicators in moving heaving areas.

In terms of device speed, a pile foundation with a grillage is inferior only to an analogue made only of screw supports. Plus, a foundation made of wall foundation blocks will be ready to give a head start to the structure in question. In both cases high speed work is due to the lack of concrete work, when it is necessary to wait several weeks until the concrete gains strength.

If the building site has a slope, then pouring a monolith on it is problematic and expensive. It will be difficult to do without this type of foundation on such a site. Only with the help of piles will it be possible to create a stable and horizontally level base for the structure. This is one of the main advantages of the foundation. All other options for him are on construction sites with difficult terrain lose immediately.

Another undeniable advantage is the extreme simplicity of execution. It’s not difficult to make your own pressed supports from asbestos-cement pipes and concrete inside. It’s even easier to make a reinforced concrete strip of small size and weight on them.

Minor difficulties here can arise only when installing the formwork suspended. It cannot be immersed in the ground. The pillars must raise the grillage part above the ground by at least 30 cm, otherwise, if there is severe heaving, it may “float” from the supports along with the building on top.

There are also disadvantages to a foundation with a concrete grillage on piles, but frankly there are few of them:

Inability to make a basement;

Costs for additional floor insulation.

The underground space of a cottage on a pile foundation with a grillage must be closed from the wind, otherwise constant drafts under the floor will blow all the heat out of the building. To do this, you can use facade panels from various materials or make masonry from beautiful facing bricks. Plus, the floor in such a house will definitely have to be insulated. It is better to immediately include these expenses in the overall estimate for housing construction.

Step-by-step instructions for building a foundation with your own hands

It is best to entrust the calculation and preparation of a foundation project for a house, whether it be a pile-strip foundation, to a professional designer. If the piles are chosen incorrectly in height and thickness, then it will take a long time reinforced concrete support and the building will not last on it.

Marking on the site

At the same time, it is also not worth setting parameters “in reserve”; this will only lead to an increase in the cost of work. As such, constructing a foundation of the type in question with your own hands should not cause difficulties. Below is a short step by step instructions will allow you to quickly understand all the nuances of this process.

To make a foundation from bored piles and a monolithic grillage, you must:

The bottom edge of the supports should be below the freezing point of the soil. In this case, the holes for the piles are made 10–15 cm wider than the asbestos-cement pipes taken. In order for the pillars to stand more firmly in place, an expanding concrete base is installed in their lower part. Holes in the ground for supports are made in width just to fit its dimensions.

Waterproofing of concrete is carried out with roofing felt or mastic. Even flexible tiles made from modified bitumen. True, it will cost more than regular roofing felt.

Usage

Comparing the pros and cons of the pile-grillage foundation structure, it is immediately clear that the former are much more numerous than the latter. Such a foundation is suitable for both small outbuildings and one-story private houses made of foam concrete or brick. At the same time, you can do everything yourself without any problems. Not much earthwork and concrete work will have to be done, and the construction of the structure itself is extremely simple.

Until recently, only four types of foundations were common in construction: pile, strip, slab and columnar. Moreover, preference was given mainly to the strip type - it is laid below the freezing point of the soil, thanks to which the building stands reliably, but this zero level is expensive. How long? By as much as 45% of the estimated cost of all work! That is why the new Finnish type of zero-level device - the pile-grillage foundation - began to gain popularity so quickly. Especially its subtype, which is constructed in permanent formwork. And it comes out within 10-25% of the total estimated cost for the bathhouse - all thanks to the fact that there is no need to install shields and mount them wooden blocks, and dismantling of hardened concrete is also not necessary.

And also pile-strip foundation(it is also called that) copes with its task perfectly on slopes, areas with uneven terrain and on unstable ground. If the bathhouse is planned to be massive and not have one floor, just such a zero level will withstand everything.

What is a grillage and why is it needed?

A grillage is slabs or beams that connect piles to each other already on the surface of the earth. This foundation design is simply ideal for baths that are built according to frame technology and their main elements are associated with piles, and when the width of the strip foundation is planned to be too wide.

So, in such a foundation for a bathhouse, the grillage can be monolithic, prefabricated, or prefabricated-monolithic. If it is monolithic, made of concrete with formwork, it is also a strip foundation on bored piles, which is no less strong and durable.

Which piles are best for such a foundation?

According to the materials, piles can be reinforced concrete, concrete, metal and occasionally wood. There are also hanging piles that transfer the load of the bathhouse to side surfaces, and rack piles - which transfer the same weight to the mother soil.

A modern pile foundation with a grillage is made today with both cast-in-place piles, which are conveniently laid in prepared holes right on the construction site, and injection piles - they are poured into narrow holes up to 12 cm with single reinforcement. A good alternative is driven piles - ready-made pillars that are driven into the ground using special equipment.

How to properly position piles in a grillage?

In total, there are 5 ways to arrange piles in a pile-grillage foundation:

Single - when the piles are each under their own support.
Tape - when they are evenly located around the entire perimeter of the bath.
In the form of strips - when piles are placed in 2 or more rows in a long grillage. This is for huge and massive baths with pools and floors.
Bushes - piles are located in places of high load and under load-bearing columns.
In the form of a field, the piles are arranged in rows or in a checkerboard pattern under a large grillage.

Construction of such a foundation in a step-by-step manner

Piles for such a foundation will need to have a round cross-section, and they will be driven into the ground thanks to the work of a construction drill. After drilling the wells, a sand cushion will be laid in them in a layer of 30 cm. Prepare for the fact that there will be a lot of piles - both at the base of the walls and at the corners of the strip, and at a distance of at least 1.8-2 meters from each other. Asbestos-cement pipes and those made from ordinary roofing felt using fishing line are traditionally used as waterproofing for such a foundation.

The simplest version of a pile-grillage foundation is piles buried 2 meters and 3 m apart from each other, and a grillage in the ground 20 m deep. And then inside the grillage you can build an underground floor on a sand cushion or screed - then there will be no need for waterproofing . Cheap and cheerful, as they like to say in Russia.

Step 1. Geological exploration work is carried out, which allows us to understand what kind of soil is on the site and how homogeneous it is. Moreover, if it is not possible to bring a specialist, you need to at least do all this in a primitive sense - after all, it is known that the characteristics of the soil can be different within a very small area. In addition, parameters such as wind load, weight are also important. building materials baths and the magnitude of the relief slopes - all this is also taken as a basis.
Step 2. A sand cushion is prepared for the reinforced concrete foundation strip - so that the entire structure is maximally protected from the mechanical influence of the soil.

Step 3. Traditional formwork is made, as for a strip foundation - according to the same principles. As for the pile-grillage foundation with permanent formwork, the role of “dishes” in it is played by extruded polystyrene foam “Penoplex” or “ThermoMonolit”. As a result, the foundation itself turns out to be warm and even waterproofed. And all the cold bridges will be eliminated fiberglass reinforcement and SVT-ties.

Step 4. Piles are made. The holes for them are drilled with special equipment, then they are lined with roofing felt or similar sheet material - with the expectation that the upper part is located at ground level. Moreover, an asbestos cement pipe can be used as casing. But four threads of reinforcement are placed inside the hole - connected to themselves so that their upper part comes out of the pile and is connected to the grillage reinforcement. This is where the concrete is then poured.

But before reinforcing the grillage, the upper part of the piles is first waterproofed from it - the amount of material is calculated individually. But the reinforcement that is released from the piles is tightly connected to the grillage reinforcement. After it reaches 50% strength, the bedding can be removed and a grillage above the ground will be obtained - it should not rest on the ground.

Step 5. The piles and strips are reinforced together and filled with concrete - for these purposes it is best to use construction vibration equipment. This is, in fact, a strip foundation on piles, which is officially called “pile foundation with a monolithic grillage.” Moreover, the piles are poured first - and only after a long period of time can the entire reinforced concrete strip be concreted. And, more precisely, exactly a week later, when the concrete has already gained half of its brand strength, work on the grillage begins. So, first, formwork is constructed, where sand is poured or polystyrene foam is laid. This is necessary to raise the grillage above the ground and align the bottom of the formwork with the top of the piles. By the way, this foundation can be filled with self-produced concrete.

But the pile-grillage foundation also has its disadvantages. Firstly, ground floor the steam room will not have one, such a structure cannot be installed under heavy walls, and the calculations themselves for a pile-grillage foundation are quite complex. But for an ordinary Russian bath, the option is almost ideal.

Until recently, only four types of foundations were used for the construction of residential buildings - strip, slab, columnar and pile. The most common was the tape type, since the depth of its placement depends on the freezing of the soil. This guarantees that the structure being built will be reliably protected. But recently, the pile-grillage foundation, which has a lot of positive qualities at a much lower cost, has become especially popular.

What is a pile-grillage foundation

To understand in more detail what a pile-grillage foundation is, we should recall the structure of a classic pile foundation. This is a load-bearing structure, represented by a certain number of piles buried in the ground. The piles are buried along the perimeter and area of the future structure with a certain step, which is calculated based on the design load.

To tie the pile foundation, a grillage made of wooden beams is used

The main disadvantage of a pile foundation is poor load distribution between the supports. Therefore, this type of load-bearing foundation is used only for small log and frame buildings.

The pile-grillage foundation is a modernized version of the pile foundation. The load-bearing supports are combined using a wooden, concrete or reinforced concrete grillage, which is laid on piles.

Thanks to the rigid connection between the supports, the load exerted on the foundation is distributed more evenly. This makes it possible to use a grillage-type pile foundation for the construction of buildings made of blocks and bricks.

How does a grillage work?

The grillage is the upper horizontal part of the pile foundation, combining the load-bearing supports into a single structure. This foundation element accepts and evenly distributes the load from the walls of the building onto supports in the form of piles. The load-bearing elements, in turn, transfer the load to the ground.

The height of the supports of a pile-grillage foundation depends on the depth of soil freezing

In fact, the main task of the grillage is to combine piles into a single structure, which significantly improves load distribution, prevents individual piles from sinking into the ground, and reduces the risk of damage load-bearing walls and other structural components of the building.

Depending on the method of execution, the foundation grillage can be prefabricated or monolithic. The most illustrative example of a prefabricated grillage is a belt of steel beams, which are fixed together by welding. Basically, prefabricated grillage is used for non-residential buildings designed for 15–20 years of operation.

A monolithic grillage is a more integral and durable structure, for the manufacture of which various materials are used. For example, a popular type of monolithic grillage is a reinforced concrete strip. Sometimes this type of grillage is also called strip because of some similarity with the type of foundation of the same name.

The ground grillage should be located on a sand cushion up to 30 cm thick

Depending on the position of the structure relative to the ground, the following types of grillage can be distinguished:

hanging - located above the ground at a distance of 10–15 cm or more;
ground - the grillage lies on the surface of the ground without being buried in the ground;
recessed - the lower part of the grillage is located below the ground level and rests on a sand and gravel cushion.

When constructing residential buildings, the hanging or so-called high type of grillage is most often used. The distance between the soil and the lower plane of the grillage protects the main structure of the foundation from deformation and tearing out of especially heaving types of soil.

The presence of a void between the soil and the floor of the building allows the subfloor to be constantly ventilated, which reduces the level of humidity in the premises of the house or bathhouse. Ground and buried grillage is used during construction low-rise buildings when a more durable base with improved thermal insulation qualities is required.

Advantages and Disadvantages

The advantages of a pile-grillage foundation include the following:

A pile-grillage foundation is recommended for construction not only on mobile and weak-bearing soil types, but also on soils with increased density, when preparing a pit and carrying out other earthworks for strip or monolithic foundation unjustified.

Among the significant disadvantages of this foundation, it can be noted that in the houses being built it is unlikely that it will be possible to equip a full-fledged basement floor. Even when installing a pile foundation with a recessed grillage, a large investment will be required to obtain an insulated and functional room.

When arranging the foundation, special equipment is necessarily used to drive piles to the required depth. This does not apply to significant shortcomings, but before constructing the foundation, you should not only calculate its load-bearing capacity, but also think over a plan for the passage of equipment.

How to make a pile-grillage foundation

Before proceeding with the construction of a pile foundation with a grillage, you should carry out preparatory work. To do this, you will need to decide on the type of load-bearing supports and calculate their minimum number. After this, you need to draw up a project or plan diagram, where you will need to place the supports according to the dimensions of the future structure.

Which piles are best to use?

Depending on the method of immersion in the ground and the main material from which the support is made, the following types of piles can be distinguished:

IN industrial construction In addition to the listed types of piles, vibratory-driven and pressed types of piles are used. Screw piles are optimal in terms of price-quality ratio. Their load-bearing capacity is sufficient for the construction of timber and log low-rise houses.

According to their design, screw piles are divided into three types: single-bladed, multi-bladed, narrow-bladed. Single-blade piles are rarely used due to their low performance qualities. They are the cheapest and most accessible type of products for the construction of pile foundations.

Multi-bladed screw piles are used in the construction of houses on most types of soil. They have high strength and performance qualities. Capable of supporting the weight of one- and two-story buildings weighing more than 70 tons.

Screw piles allow you to arrange a grillage made of timber, channel, I-beam and reinforced concrete

Narrow-bladed screw piles are a specialized type of product designed for the construction of pile foundations on rocky and hard soil types. Due to the reduced diameter of the blades, the piles are easily screwed into rocky soil. At the same time, the small diameter of the blades is quite enough to hold the support.

Location of piles in the grillage

When arranging a pile-grillage foundation, there are several ways to arrange the piles:

How to place piles on a house plan

In order to independently position the piles along the perimeter and area of the site where the foundation will be built, you need to know the parameters of the building being constructed. Based on this, an approximate plan diagram is drawn up showing the base of the structure and piles on a reduced scale. To do this, you can use plain paper and a pencil.

Load-bearing supports must be located at corners and at intersections with partitions. If the distance between the supports exceeds 3 m, then an intermediate pile must be installed in this area. The optimal distance between intermediate piles is 2–3 m. After the piles are located, you can proceed to their selection, taking into account the method of deepening and material.

When drawing up a diagram, the dimensions and distance between the piles must be indicated

The exact number of piles and their supporting area depends on the design weight of the building being constructed. The load-bearing capacity of piles of a certain type must be indicated in the specification for the product, which can be found on the manufacturer’s website or at the point of sale where the piles will be purchased.

Based on the distance between the piles and their load-bearing capacity, the minimum required number of products is calculated.

Calculation of pile-grillage foundation

As an example, let's calculate the number of screw piles required for construction frame house, having a size of 8x8 m. The total weight of the building will be 30 tons. The structure will be built on medium-density soil.

The step between piles should not exceed 3 m

The calculation of piles for the foundation is carried out in the following sequence:

The total load on the foundation is 30000 + 9600 + 11520 = 51120 kg. Taking into account the reliability coefficient: 51120 * 1.1 = 56232 kg.

The number of piles is 56232 / 2000 = 28,116 pieces, but since the pile is a solid product, in our case we will need 29 pieces. Pile length 2500 mm. The step between supports is 2 m.

The coefficients used in the formulas were taken from SNiP 2.01.07–85 “Loads and impacts”.

Foundation pouring technology

After drawing up a plan and calculating the minimum number of piles required, you can purchase material and begin preparing the site for the foundation. To do this, you will need to mark the selected plot of land and perform excavation work.

Marking the space for the foundation

To mark the area for foundation construction, wooden pegs and nylon cord are used. First of all, it is necessary to carefully level the area using improvised means and garden tools. If the area is very relief, then special equipment may be needed to give the area a uniform slope.

After installing the pegs or steel rods, a nylon thread is stretched between them

Further steps for marking the space for the foundation are as follows:

The result should be a marking showing the dimensions of the load-bearing foundation. This will allow you to determine the points where the piles will be screwed in or poured.

Excavation and pouring of piles

The excavation work that needs to be done before building the foundation largely depends on the type of piles chosen. To construct a grillage-type pile foundation intended for residential buildings, screw or bored piles are most often used.

Screw piles are screwed into the ground manually or using a special installation without prior preparation of the well. A cord is used as a height guide, which is stretched relative to the horizon.

Preparation of wells and pouring of bored piles is carried out as follows:

Using special equipment, wells are drilled in the ground to a depth of 80–100 cm. The diameter of the well depends on total weight structure and cross-section of the nozzle used. If necessary, the well can be expanded using a regular shovel.
Before pouring concrete mixture a reinforcing frame is installed in the well
The inner walls of each well are cased insulating material. For example, you can use regular roofing felt. To do this, you need to cut a sheet of roofing material 50–70 long and carefully insert it into the hole.
After isolation, a 5 cm layer of gravel of fraction 20–40 is poured onto the bottom of the well, which is lightly compacted with a wooden lath. Next, a reinforcing frame made of steel reinforcement Ø18–22 mm is installed in the well.
Concrete grade M500 is used for pouring bored piles
The standard version of the frame consists of 4 rods connected by crossbars made of reinforcement Ø 14–16 mm with a pitch of 20 cm. An approximate knitting pattern is shown in the photo above. Upper part the frame must extend 15–20 cm from the well. This is necessary for its further connection with the grillage.
After all the preparatory steps, the concrete mixture is poured. For this purpose, use concrete grade M500 from the manufacturer. If you plan to mix the solution yourself, it is recommended to use a concrete mixer and ready-made dry mixes.

If capabilities and skills allow, the frame can be knitted by welding. Otherwise, stainless steel wire is used. When pouring piles, it is recommended to tamp the concrete. This can be done using a steel reinforcement bar or wooden slats. This will help prevent voids from forming in the concrete.

Arrangement of grillage and installation of formwork

Welding is used to install a grillage made of steel beams. During the work, it is necessary to weld the prefabricated grillage structure to the pile heads in the form of a reinforcing frame.

The grillage reinforcing belt must be securely attached to the pile frame

To install a recessed reinforced concrete grillage, you will need to do the following:

Instead of a regular board, you can use thick plywood or metal sheets to make formwork. When making formwork, it is worth remembering that its height should be 5–10 cm higher than the level of the grillage.

Installation of embedded parts and filling of grillage

Before pouring the concrete mixture, it is necessary to lay pipes, which will later act as channels for various communications: heating, sewerage, water supply.

Vents are installed on opposite walls of the foundation or grillage

And also vents should be provided in the grillage design. They are usually located on opposite sides of the foundation, which provides a natural level of traction without installing additional devices.

To install ventilation holes and further fill the grillage, you will need to do the following:

A short pipe is laid inside the reinforcing belt, the length of which is equal to the width of the future foundation. You can use a longer pipe, but this will require cutting a hole in the formwork using a drill with a wood core bit.
The pipes are laid at a certain pitch on opposite walls of the future grillage. If the foundation includes internal partitions, then pipes are also installed in them. An approximate diagram can be found in the photo above.
The ventilation pipe is laid between the reinforcement cage bars
After laying the pipes, you can proceed to preparing a concrete mixture based on M500 cement. Before pouring, the protruding part of the piles and inner surface The formwork is insulated with roofing felt.
The concrete mixture is poured from any corner of the formwork. During the pouring process, concrete is compacted using a special tool or improvised means. It is important that the complete filling of the grillage be completed in one work shift. The top layer of concrete is leveled using a rule and checked for level.
Complete hardening of concrete will occur within 25–28 days from the moment of pouring
After pouring, the structure is covered with plastic film. If the grillage was poured at a temperature above 20 o C, then after 4–5 days the formwork can be removed, and after 7–10 days further construction work can begin.

If the work on arranging a pile-grillage foundation was carried out at temperatures below 10–15 o C, then the formwork can be removed only after 14–16 days.

Video: do-it-yourself pile-grillage foundation

A pile-grillage foundation is the most successful design of a load-bearing foundation, which combines the high performance qualities of a strip and pile foundation. This type of foundation is perfect for the construction of residential buildings using frame technology, as well as for the construction of baths, saunas or technical buildings.