How to build a pile foundation with a monolithic grillage

The pile-grillage foundation is most in demand among owners of suburban areas. In dense settlements, it is impossible to use heavy special equipment (hammers, pile drivers) for driving driven piles with a design length of more than 10 m or for light buildings. Renting this equipment is expensive, so short suspended bored piles with a monolithic grillage are used.

Construction of a pile foundation with a monolithic grillage.

Pile-grillage infill foundation.
To save construction time, budget and at the same time give durability to the building, a variety of construction technologies are used. This applies to all elements of the building, from the foundation to the roof. Let's consider what a monolithic pile foundation is, made using a monolithic grillage. This type of foundation is used for the construction of low-rise buildings. A monolithic pile foundation is not as strong as other types, but this is compensated by the complete absence of excavation work. And one more advantage - you can start building it even in winter. A pile foundation with a monolithic grillage is used mainly on soft soils or with a high freezing depth.

You can build a pile monolithic foundation using the following steps:

1. Survey and earthworks.
2. Installation of supporting elements (piles).
3. Installation of grillage.
4. Construction of the basement.

Materials used in the construction of a pile foundation:

Scheme of pile foundation foundations.

Diagram of a pile-grillage foundation: 1 – bored pile made of monolithic concrete and frame made of reinforcement; 2-grillage made of monolithic concrete and frame made of reinforcement;3 – horizontal waterproofing; 4 – vent.

A monolithic pile foundation is made from various materials. Piles are made from concrete mixture. The structural system itself is made from prefabricated or monolithic reinforced concrete, as well as steel and wood.

In general, the entire process consists of the same stages as in the construction of any other foundation, but still, at each stage you can encounter its own unique installation operations, characteristic specifically for a pile foundation.

Curing

The process of dismantling the formwork
Concrete hardens and gains full strength within a few weeks. All this time, you need to protect the grillage from excessive exposure to the external environment. To protect the concrete surface from precipitation, make a cover from a polymer film. In hot weather, cover the surface of the grillage with a wet rag. After the foundation is ready, the formwork is dismantled.

Excavation.

Boer.
Using a hand drill, you can drill holes for piles up to 5 m deep and no more than 30 cm in diameter.

During excavation work, an earth drill is used to construct a pile foundation. It is a device of two rods with a loosening and cutting cup. The drill makes small holes under the piles. You can use a hand drill, which drills holes up to 5 m. It is used when the diameter of the foundation support is no more than 30 cm. A motorized drill is used when it is necessary to drill a hole of a large diameter (from 50 cm). That is, when constructing a small pile foundation with a grillage, you can use manual labor, and if screw piles are used in the structure, then you can simply abandon the excavation work. There are several varieties of this tool: TISE-F, TISE-2F, TISE-3F.

On one side the drill has a soil accumulator, and on the other there is a crossbar with handles. A folding plow is mounted above the soil accumulator. When drilling, the plow cuts off part of the earth. Under the influence of its own weight, the plow cuts the soil, gradually lowering down. The cut soil falls into the storage tank and rises to the top. This drill weighs 11 kg. When drilling, direction should be taken into account.

If, for example, you need to drill a well deeper, then the drill must be rotated clockwise. If anchor extension is required, the tool is rotated counterclockwise.

Sod should be removed before drilling. Depending on the type of soil, drilling can be done either by one person or by two people. A partner is involved if drilling occurs on clay or dense soils.

Installation of grillage.

Steel grillage.
A grillage made from I-beams is highly expensive and difficult to install.

A grillage is a part of a pile foundation that combines load-bearing elements into one structure. They are made in the form of a strip or in the form of a slab. If a wooden structure is being erected, then the functions of a grillage are performed by the crown of beams located in the lower part. The steel system is based on I-beams. But such a pile monolithic foundation has several disadvantages. Firstly, a monolithic pile foundation, in which I-beam products are used, is highly expensive. Secondly, the installation process itself is labor-intensive and requires the use of special equipment. It is impossible to mount this part of the foundation manually. Thirdly, even steel treated with a special solution will soon corrode. Therefore, the only method left is using reinforced concrete. In this case, the grillage can be prefabricated.

The types of grillage designs vary, depending on the position in relation to the ground. The first type is tall. This is the most popular type and is located 0.1-0.15 m above ground level. This distance is quite enough to reduce the impact of the soil on the connecting system during heaving. Swelling of the soil due to weather changes is accompanied by raising the grillage and tearing out the pile elements. It is also possible to tear off the structures themselves from the piles. But a height of 0.1-0.15 m allows you to avoid such problems.

Pile foundations come with a low, raised or high grillage.

A monolithic pile foundation with a high grillage has one drawback - the free space between the floor covering and the soil. In this regard, additional thermal insulation is required.

Another type of grillage is an elevated one. The base of the system is located on the soil. Unlike the previous type, here there is no free space between the floor and the soil. To prevent the effect of heaving on the structure, part of the soil is removed from under it - approximately 0.1-0.15 m.

The next type of grillage is recessed. It is made below ground level and some soil is also removed from under the lower part.

The main task of the grillage is to connect all the piles into one system. The structure does not distribute any loads over the ground. It simply applies pressure to the piles. The grillages are not mounted directly on the ground so that sections of the base do not come off due to soil heaving.

Existing types

Types of pile foundations are distinguished by the type of piles.

There are:

• Rack piles. They are immersed in the ground until hard contact with dense soil layers appears. They form the strongest supporting structure and are capable of supporting buildings of any weight and number of storeys.
• Hanging piles. The load-bearing capacity of these supports depends on the frictional force on the side walls and on the strength of the soil cushion under the tip, formed during immersion. This design is convenient when dense layers of soil are too deep, but can suddenly change its parameters due to changes in groundwater levels or other processes.

The materials for making piles are:

• Wood. The most ancient and traditional material, which has many disadvantages. With the advent of other, more stable and durable types, wooden piles have practically disappeared from the arsenal of builders, although they are still used in some places (in private construction, for the construction of auxiliary buildings).
• Metal. Driven piles are not specially produced; in this role, pieces of rails, channels or I-beams of suitable size are used. Screw piles are manufactured completely ready for use. The specificity of the metal does not allow for durable supports due to corrosion caused by electrochemical processes and the presence of stray currents.
• Reinforced concrete. The most common type of piles. The most durable are driven ones, manufactured using special technology using stressed reinforcement. Bored piles are cast from concrete directly on the site, which is convenient, reduces transportation costs and the overall level of use of construction equipment, but significantly increases the production time due to the need to cure the concrete to gain structural strength.

There are three main types of pile foundations:

• On driven piles. The immersion of trunks is carried out by special machines. The process does not take much time, the supports are strong and reliable. The disadvantage is the impossibility of carrying out work near the buildings in use due to soil movements that occur during immersion.
• On bored piles. This type of piles is convenient because it does not require transportation, unloading, or the use of lifting equipment. A sleeve (a type of formwork made from roofing felt or plastic pipe of suitable diameter) is lowered into a pre-prepared well, a reinforcement frame is installed and concrete is poured. All operations can be performed independently, but a fairly long period of holding the piles will be required for the concrete to harden.
• On screw piles. They are made of steel pipes with a wall thickness of at least 4 mm. The lower part has a welded or cast pointed tip and spiral cutting blades. Driving screw piles resembles the process of screwing a screw - the blades provide immersion, the sharp tip pushes apart or splits the obstacles encountered. Screw piles can be installed manually, if necessary, they are removed and reused in other places. The service life depends only on the intensity of corrosion.

NOTE! All pile foundations cannot be created on rock or coarse rocks.

Foundation reinforcement.

Construction of pile foundations.
Foundation reinforcement increases the strength of concrete.

Mandatory reinforcement of the foundation with a monolithic grillage solves a number of useful problems. The resistance of concrete to bending loads increases. Without reinforcing elements, the grillage may crack. All reinforcement work consists of creating two belts. The first chord is located at the top, and the second at the bottom, and each uses at least two reinforcements. The diameter of the reinforced rods should be within 1-1.2 cm. The rods neutralize the deformation effect.

Transverse reinforcement has nothing to do with the load. Its purpose is to knit the entire structure into a single system. Since there is no pressure here, reinforcement with a diameter of 0.6-0.8 cm is used. In addition, smooth reinforcement products can be used.

The reinforcement cage must be completely buried in the concrete mixture. Only the very top section should protrude 2-5 cm. Such belts are a kind of mesh, which consists of ribbed reinforcement. There should be a step of 0.2-0.4 m between the elements. Due to the vertical rods, the upper and lower sections are combined into one structure.

It is important to note that the construction of a foundation with a grillage requires more concrete mixture than for other types of foundations . Before pouring, formwork is installed, into which the reinforcement frame is mounted. To ensure that the steel structure is properly immersed in the concrete mixture, bars are placed under the lowest bars. All elements must be securely fastened.

Reinforcement is also used to reinforce piles. This is necessary to connect to the grillage and strengthen the concrete. To attach the grillage to the piles, surface rods are attached to a frame made of reinforcement. The width of the grillage is made larger than that of the walls, and the cross section is made in the form of a square.

Insulation scheme

Waterproof materials are used for insulation:

• Liquid polyurethane foam.
• Extruded polystyrene foam (penoplex).
• Styrofoam.
• Expanded clay.
• Foam glass, etc.

The most convenient and effective option is considered to be penoplex, which is glued in a dense layer to the entire surface of the grillage, both internal and external.

It is somewhat worse, but much cheaper, to use polystyrene foam , which is also resistant to moisture and is an excellent heat insulator, but has the ability to crumble and is excessively brittle.

Construction of the basement.

After the pile monolithic foundation is built, we proceed to finishing the base. The upper edge of the basement trim is attached to the bottom of the house and is protected from above by a special galvanized canopy (shimmer). From below, the finishing does not reach the ground by several centimeters. This is done so that during soil heaving the base is not subject to deformation. To remove precipitation, drainage is installed, and a concrete blind area about 70 cm wide is made. The best solution for a blind area around the entire perimeter of the house is paving slabs. It is durable, aesthetic and repairable.

Calculation

To make the calculation, you need to collect all the information about the territory on which the structure is planned to be erected.

For calculations you need information about:

• physical and geographical conditions;
• geological structure;
• hydrological conditions;
• physical properties of the soil.

Based on this information:

• grillage parameters are determined;
• loads are calculated;
• the depth of placement is calculated;
• the required number of supports is determined;
• the diameter of the piles or pillars is calculated.

It is advisable to entrust this work to specialists, since the slightest mistake in calculations leads to disastrous consequences.

Pile-grillage foundation - review of technology.

A pile-grillage foundation is not yet as popular a type of base for a building as a strip, pile or monolithic one. It began to be widely used relatively recently. But, as it turned out in practice, when building houses on loam, highly heaving or peat soils, this type of foundation is the most optimal. It takes into account and compensates for insufficient soil stability, thereby ensuring the stability of the building. An undoubted advantage is the savings of about 30% compared to the price of a traditional foundation.

Construction of grillage foundations.

Features of the foundation structure of the grillage type.

The grillage is essentially beams (slabs) through which piles located on the ground are connected to each other. These concrete lintels play the role of supporting structures for the structures erected on their basis.

Based on the amount of materials used, grillage systems are:

Classification of structures with grillage depending on load distribution:

1. a high foundation that takes the weight of the building through the piles and distributes it to the lower layers of the soil;
2. low, located below the soil surface and transmitting the load along the base.

Where is a pile foundation with a grillage used?

The construction of a grillage-type foundation base is carried out on soft soils. These include:

• highly heaving;
• peat and silt;
• loess-like;
• clayey mobile;
• loams;
• quicksand

This type is also used if:

• a house is being built on a mountainside or on a site with complex terrain;
• construction is carried out using frame technology;
• the depth of soil freezing exceeds 1.5 m.

The grillage type is also ideal in the situation where the calculations show that the strip foundation for a brick house should have a width of more than 1.5 m.

Pile foundations with a monolithic grillage are used for the construction of small country houses, light brick buildings, houses made of central fiber board, laminated veneer lumber, foam concrete and other similar building materials. The grillage for the above buildings can be monolithic or precast reinforced concrete.

Foundation layout diagram.

Laying depth - what it depends on

The depth of placement depends on the condition of the soil on the site.

All related factors are taken into account:

• Groundwater level.
• Availability and volumes of soil water.
• Possibility of flooding in spring.
• The presence of seasonal changes in hydrogeology, an increase or decrease in the degree of filling of all aquifers.

To select the correct depth, it is often necessary to collect information from local geological and meteorological departments, consult with experienced builders, and refer to various SNiP applications.

It must be taken into account that all values ​​​​indicated in various sources are minimum, i.e. it is allowed to increase the lifting height, but it is impossible to reduce the gap height .

Installation stages.

The construction of a pile foundation with a grillage begins with driving the piles into the ground. A prerequisite when working is to accurately determine the level of soil freezing. The supports must be buried below this mark. Next, the piles are connected with grillages. By their nature, grillage joints can be made from the following materials:

Grillages protect against soil displacement. They counteract structural instability during freeze-thaw and provide rigid coupling of the building's structural elements. Piles are mounted at points where the heaviest load is expected; their length depends on the depth of soil freezing.

In practice, for the construction of low-rise buildings, supports from 1.5 to 3 m are used. The distance between adjacent elements is 1-1.5 m. The holes for the supports must be lined with roofing felt or similar material. It is possible to casing with asbestos-cement pipes.

4 reinforcing rods are vertically fixed and securely tied in the hole. The top of the pile must be above ground level. The reinforcing thread coming out of the pile support is tied to the grillage reinforcement. The holes are filled with concrete mixture.

Over the course of a week, the concrete will gain strength. After 7 days the indicator will reach 60%. After this, you can begin work on reinforcing the grillage. The process begins with formwork. Sand is poured into it or polystyrene foam is laid. Thus, the grillage will be raised above the ground (hanging on stilts).

Scheme of a pile-grillage foundation.

An important point before reinforcement is waterproofing the upper part of the pile pillars. This stage should not be skipped under any circumstances. Reinforcement is carried out according to the general scheme developed for a specific construction. This is due to the fact that the position of the supports and the distribution of loads on the grillage differs in different places of the structure. The backfill from under the grillage structure is removed after the concrete reaches half of its brand strength (no earlier than 7 days).

Taking into account the fact that for each specific case the position of the supports and the distribution of the load in the grillage is different, reinforcement is carried out on an individual basis. The reinforcement that comes out of the piles is connected to the grillage reinforcement. When the grillage reaches more than half of its brand strength, the bedding from under it is removed. The grillage structure hangs on stilts. The grillage is not allowed to rest on the ground between the piles.

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Pros and cons of a pile-grillage foundation

Like every other building structure, the pile-grillage structure has its own advantages, disadvantages and limitations in application.

It involves minimal time spent on creating a foundation, provided that the work is carried out by experienced craftsmen with their own special equipment. A pile foundation for a brick house (or other type of structure) is installed in the shortest possible time. The customer receives a ready-made turnkey project.

It involves the use of a small amount of concrete due to the fact that there is no need to build a cushion in the ground.

In the cold season, when the soil freezes, the area of ​​interaction between the elements of the pile-grillage foundation and the frozen ground is minimal. Thus, the heat loss of the building is also small.

• The presence of vibration-isolating properties in the structure.

The peculiarities of connecting piles with a grillage provide reliable protection of the structure from vibration associated with the close location of the building relative to large highways, railways or subways. A pile foundation without a grillage is less effective in such cases.

It should be noted that the construction of a pile-grillage structure can be carried out at almost any time of the year. Restriction – work cannot be carried out at temperatures below -10 °C. Another advantage of such a foundation is the affordability of the materials used.

Bored piles.

Disadvantages and disadvantages:

• Use of special equipment.

It is impossible to build this type of foundation yourself. The technology requires the mandatory use of special equipment.

It is almost impossible to build this type of foundation with your own hands.

• The difficulty of constructing basement floors.

Features and layouts of supports complicate the arrangement of basements and basements. Often the space between piles has to be filled, which significantly increases the final cost.

• Low resistance to rollover.

Pile-grillage foundations on subsiding and swelling soils require special precision in adherence to technology.

Installation of driven supports.

Turnkey foundation cost.

Due to the difficulties of independently implementing the idea of ​​arranging a foundation with a grillage, an important point is the price for the work of the team and the rental of special equipment. Another nuance that affects the final estimate is soil testing and design calculations. In both cases, a balanced approach is required from the customer. On the one hand, he cannot hire non-specialists, since the durability and reliability of the structure is at stake. But there is no need to pay an inflated price either. The optimal solution is to consult friends who have already gone through a similar stage of construction.

The construction price in the Moscow region averages 4,400 – 6,000 rubles per 1 linear meter. The total amount is affected by the number of piles, their quality and size, the total amount of materials, and installation technology.

Construction cost per linear meter.

What is a pile-grillage foundation?

Everyone probably imagines a pile foundation: it is a number of piles buried in the ground to the level of the load-bearing layer or below the freezing level. In its 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 the supports are tied using a tape made of metal or reinforced concrete (concrete) into a single structure. This tape is called a grillage.

Pile grillage foundation.

This is what a pile-grillage foundation looks like when taken out of the ground.

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.

Foundation grillage.
There are pile foundations with high and low grillages.

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 provide?

Any house in different parts will have 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.

Pile grillage foundation.

What is the difference between pile and pile-grillage foundations?

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, the 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 - depending 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.

Pile grillage foundation.

Construction of a pile-strip foundation.

How does he work? The load from the house is transferred to the belt. Thanks to the presence of longitudinal reinforcement, it is 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, when heaving forces begin to affect 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.

Useful tips

The pile-grillage foundation must be erected correctly, adhering to all construction technologies - this will help increase its technical and operational characteristics.

If construction work is carried out by novice craftsmen, then they need to take into account some recommendations from experienced specialists.

• The installation should begin with calculations. To do this, the type of soil and the depth of the grillage are determined. If the depth of the support is insufficient, the building may shrink and crack, and then even collapse.
• A huge role is played by soil research, on which the bearing capacity of the structure depends. Rocks and rocky soils have the highest rates. If the composition of the soil is incorrectly determined, this will lead to errors in calculating the load of the structure, as a result of which it will sink into the ground.
• There must be a good connection between the piles and the grillage, since under the influence of soil pressure the unstable structure can collapse.
• Regardless of the type of foundation, a sand cushion must be laid to the freezing depth - this is especially true for the operation of the foundation in winter. Frozen soil can expand and cause grillage ruptures.

• The grillage should not be in contact with the surface of the ground or be buried in it. It is necessary to remove a small layer of soil along the entire perimeter of the site, then install the formwork, fill it with sand and pour concrete.
• The step between piles must be accurately calculated. This indicator is determined in accordance with the load on the foundation, the diameter and amount of reinforcement.
• During reinforcement, it is worth providing the required number of ventilation ducts. All internal compartments must be connected to exits to the street.
• Insulation and waterproofing play a huge role in the construction of the base. They should be laid before the foundation is poured with concrete.
• The bottom of the pit or trench must be compacted and not loosened. Do not allow soil from the walls to fall onto the base. In addition, sedimentary water must drain away from the trench or pit, otherwise the bottom will become wet and will be unsuitable for filling with mortar. Excessive steepness of slopes in trenches is also unacceptable.
• Weak soil requires reinforcement with piles and good backfill.

• The sand that is used to backfill the air cushion must be moistened and the cushion must be distributed under the contour, cut off at an angle of 45 degrees.
• The formwork must be securely fastened, since when poured with concrete it may not withstand the load and collapse. Deviation of the formwork from the vertical by more than 5 mm is not allowed.
• The height of the foundation is made with a small margin of 5-7 cm from the height specified in the project.
• When reinforcing the frame, it is recommended to use rods with a total cross-sectional area of ​​at least 0.1% of the area of ​​the concrete element. In this case, it is best to choose smooth fittings that do not have traces of rust, dirt and paint.
• It is undesirable to fasten the reinforcement by welding - this may compromise its strength at the joints.
• The brand of concrete for pouring should be chosen depending on the design of the base and the climatic conditions of the region.

To learn about the design features of a pile-grillage foundation, see the following video:

When can it be used?

It is recommended to install pile-grillage foundations in the following cases:

• When unstable and weak-bearing soils go to a sufficiently large depth. These are karst, forest, peat soils, quicksand, plant and fertile soils of great thickness (more than 1.4-1.5 meters). In this case, the load must be transferred to the dense soils located below with normal bearing capacity. It is not always possible to get to them, and even if it is possible, the foundation turns out to be too expensive. Therefore, transferring the load using piles is the best choice.
• In areas with large elevation differences. In this case, it is often much cheaper to use piles of different heights than to carry out work on leveling the ground or pouring a deep tape that can compensate for height differences.

Pile grillage foundation.

• At high groundwater levels. Pile foundations are the only ones for which the groundwater level does not matter. It is important that there is soil with load-bearing capacity under the heel. The level of water location affects only the type of grillage: if the water is close to the surface, the grillage is made high, if it lies deep, it can be made low.
• During construction in hard soils. In this case, small volumes of earthworks (compared to strip or slab foundations) have a positive effect.
• If you decide to build a house using frame technology. Making a tape for it is a waste of money: you get too much safety margin, which, in this case, is useless. In this case, a pile or pile-grillage foundation is the best choice.
• With a large mass of the building (more than 350 tons). Then it turns out that the tape or plate must be very massive and, therefore, expensive. In this case, a pile-grillage foundation often turns out to be cheaper.

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.

Purpose

Unlike other types of foundations, a pile-grillage foundation ideally distributes the load-bearing loads from buildings onto the ground, so when choosing it, you can be sure that the new building will reliably serve for decades and will be protected not only from sudden temperature changes, but also from seismic activity. Such structures are widely used for both public and individual construction. They are especially suitable for areas located on a slope with heaving, permafrost soil and difficult terrain.

In addition, the following foundations are recommended:

• for building a brick house;
• in frame construction;
• for structures made of gas silicate blocks;
• on soils with high density;
• with high groundwater distribution;
• on unstable soil with quicksand.

The pile-grillage design also makes it possible to lay floors directly on the ground without additional leveling of the surface and pouring a deep tape, since piles installed at different heights compensate for all unevenness, eliminating height differences. Such a foundation can also be used in the construction of buildings weighing more than 350 tons - it will be much more reliable and economical than a strip or tile foundation. But in this case, the project will have to include an increased safety factor, which should be not 1.2, as usual, but 1.4.

What 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. They can have a round or square cross-section. They also differ in the installation method:

• Hammers. They are installed without drilling or excavation. Usually they get clogged, that’s why they are called that. They are rarely used in private construction: special equipment is required.

Pile grillage foundation.
Driven reinforced concrete piles are used more often in the construction of multi-storey buildings.

• Bored. First, a well is made in the ground, then formwork is installed and secured into it. It contains reinforcement that increases strength characteristics. Then the entire structure is filled with concrete.
• Reinforced concrete drilling rigs. In this case, wells are also drilled, but ready-made reinforced concrete piles are installed in them (driven, but with less effort).
• Screw. These are metal piles, pointed at the end and having screw blades that cut the soil. At greater depths, special equipment is required; small ones, up to 2-3 meters long, can be installed manually.

Pile grillage foundation.
One type of piles is screw piles. They can be used with grillages made of different materials for different houses.

In private construction, bored piles are most often used. They are especially popular in the construction of summer houses or baths. They can also be used in the construction of small houses. But if dachas and bathhouses 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:

Pile grillage foundation.

How do piles differ by type of work?

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 type of this type is TISE piles. They have a cylindrical extension at the bottom, which is why they transfer the load to a larger area. Also, the heel prevents heaving forces from lifting the foundation.

Feasibility of construction

Choosing this solution is advisable only if:

• you want to save money. Of course, in some cases this approach can save up to 30% of the funds allocated for the construction of the foundation. But, again, you shouldn’t go to extremes: if you see that according to calculations you need to erect several dozen piles, then it’s time to think about whether it would be easier to fill in a slab or tape;
• The quality indicators of the soil do not allow the construction of “classical” types of foundations in a minimum period of time. It often happens like this: you examine the soil yourself and notice that in terms of its indicators it is far from ideal - the groundwater level is high, the soil is completely heaving (clay, etc.), and the freezing depth for your region is rather large. In such conditions, either the slab is poured, or they rely on the type or foundation on screw piles discussed in the article;
• the load from the house is relatively low. Let’s say right away that the type we are considering is suitable for light and medium-sized structures. But in any case, the decisive factor in favor of choosing one of the types should be calculation.

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.

Pile grillage foundation.

Location of piles on the house plan.

Piles can be located pointwise - under supports (columns, racks). This arrangement is typical when constructing 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 place a house on a 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, intermediate supports are placed between them. It is advisable that the piles be located one from another at a distance of 2 to 3 meters.

Pile grillage foundation.

First, the piles are placed in the corners, then under the junctions of the load-bearing walls.

The principle is simple, but you still need to determine the required area of ​​the piles. And it needs to be calculated (or rather, selected).

Floors on the ground

Floors on the ground are used to create a grillage structure immersed in the ground. If there is an air gap, creating a ground floor becomes too difficult, ineffective and impractical.

The inside of the tape is covered with a layer of sand cushion . Then a layer of geotextile is laid on it and crushed stone is poured, onto which a layer of crushed stone is poured through an additional layer of geotextile.

The entire backfill is compacted sequentially, achieving the best possible result. Then a layer of screed is poured on which the heat insulator is laid.

A screed is again poured on top of it, inside which a heated floor system is installed.

A finishing coating can be applied to this screed . The floor cake is quite multi-layered, but it provides high-quality heating and prevents heat loss due to contact with the ground.

Calculation of a 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.

1. The weight of the house is calculated (all materials and the approximate weight of the “filling” are taken into account).
2. Based on the weight and safety factor, the required supporting area is determined.
3. Since the piles have already been placed, we can count their number.
4. 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.
5. We compare the obtained result with the reference area calculated earlier (point 4).
6. If the area found in step 4 is larger than that calculated in step 2, the selected pile parameters are suitable for us.
7. 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 bored piles.

Load-bearing capacity of piles of different diameters in different soils.

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). The coefficient of 1.4 was applied due to the fact that pile foundations require a larger margin of safety: we do not 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.

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.

Pile grillage foundation.

Schematic representation of the work procedure during the construction of a pile-grillage foundation with your own hands.

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.

For drilling, you will need either special equipment or a hand drill of a 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.

Construction of foundations for pile grillage.

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 selected, 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 technology for installing formwork for strip foundations.

Pile strip foundation.

Scheme of reinforcement of a pile-grillage foundation with a reinforced concrete grillage (pile-strip).

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 utilities will be supplied (plumbing, heating, electricity, sewerage).

Pile grillage foundation.

Don’t forget about laying pipes for vents and connecting engineering systems.

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.

Pile grillage foundation.

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.

Recommendation: A good review article, from it you can learn about the construction of a pile foundation with a grillage. Indeed, a pile-grillage foundation is not expensive. If it suits your building in all respects, then you can safely use it, but be careful when calculating the loads, you won’t be mistaken. This is an important point!

Making a base when using pillars

We've sorted out the installation of the grillage for the pile foundation, and now let's start creating a bearing plane for the columnar base.

Materials and tools

We stock up on the following set:

• “bayonet” and “selection”;
• drill;
• pickaxe;
• tape measure;
• stakes;
• chemicals to prevent the growth of vegetation;
• OSB board, plywood or edged board for making formwork;
• reinforcement frame;
• concrete mortar;
• geotextiles;
• sand;
• crushed stone;
• polyethylene;
• bitumen mastic.