Grillage: what it is, its types and purpose. Pile-grillage foundation: classification, advantages and disadvantages, requirements and standards Strip foundation with grillage

Unlike superficially similar shallow strip foundations, grillages always transfer loads to piles. There are slab, strip, and glass grillages. They come in hanging, ground, and buried types. They are made of concrete (monolith, prefabricated), profile assortment (I-beam, channel), timber. When designing, wall and roofing materials, number of storeys, region of construction, and other factors are taken into account.

Slab grillage on piles

For large dimensions of a heavy building of complex configuration, the pile fields are tied with large-format slabs. Monolithic construction is preferable; the thickness of the slabs is based on the shear force. Low grillages are laid on a standard “pie”:

• sand and gravel cushion - two layers of 20 cm each with vibration compaction every 10 cm and moistening with water
• ring drainage – at the level of the grillage base
• concrete preparation – 5 cm screed without reinforcement
• waterproofing is a standard procedure for reinforced concrete products used in the ground

Due to the slight depth of the low grillage slab, it is necessary to take measures to compensate or prevent heaving forces:

• replacing soil with non-metallic material - the technology is indicated above
• thermal insulation of the sole - by analogy with the USHP foundation, stiffeners are not needed

Hanging monolithic slab grillages are rare due to the complexity of manufacturing. Prefabricated modifications consist of one or several slabs supported on bored (less often screw) piles.

Tape pile grillage

To reduce the construction budget, a strip-type grillage is made. Dimensions depend on factors:

• width of the walls - masonry can be hung 10 cm in each direction in several rows
• number of piles in diameter - in individual construction, piles are usually mounted in one row
• height - the grillage is calculated as a beam (one span), this size is calculated in accordance with the standards SP 63.13330

Low strip grillages are laid on a concrete preparation with standard waterproofing of the base before pouring. The requirements for materials of monolithic structures are as follows:

Heaving forces are present exclusively in low grillages; they are compensated in several ways:

• cushions made of non-metallic materials + backfilling of the buried belt with sand, crushed stone
• insulation of the sole, blind area, edging - by analogy with MZLF, XPS expanded polystyrene sheets (manufactured by URSA, TechnoNIKOL and others) are laid over the waterproofing layer

Regardless of the level of the grillage relative to the surface, a drainage system is required to remove moisture from the bored piles.

Monolithic tape

Foundations, the grillage of which is poured into the formwork, have greater spatial rigidity in comparison with prefabricated structures. The grillage beams are reinforced with two chords, each of which uses at least two reinforcing bars of periodic cross-section.

In 90% of cases, a monolithic grillage is used on bored piles because:

• materials have the same resource, linear expansion
• in a monolithic grillage it is easier to wall up the heads with reinforcement bars sticking out of them
• the same waterproofing compounds are used

Regardless of the position of the monolithic grillage above the ground, it is necessary to lay drains that drain ground and surface water from the concrete piles.

Collection tape

Prefabricated pile-grillage foundations are ideal for wood construction technologies. Beams made of timber, I-beams, and channels are laid on the heads and joined in half a tree or by welding. The absence of concrete work allows:

• reduce the budget
• start building walls the next day

Prefabricated tape of reinforced concrete beams is rare and is practically not in demand in individual construction. The complexity of the design lies in the junction of two beams to the head of one pile.

The most difficult thing is to tie screw piles with a monolithic grillage. Therefore, they are usually tied with timber, I-beams, or channels. For brickwork, grillage beams made of two welded channels mounted on an edge are used.

In buildings with reinforced concrete frames, a glass grillage can be used. It has the form of a kneecap mounted on a slab with dimensions that are multiples of 15 cm, 30 cm (height, width, respectively). In this case, the total height should be 40 cm greater than the depth of the glass. Standard design calculations:

When reinforced, the spatial frame of the glass widens at the bottom - it is connected to the flat mesh of the slab. Each glass rests on 4 piles and is used for the installation of columns. Therefore, the technology is more in demand in industrial and agricultural construction.

Hanging grillage

The disadvantages of a high grillage - complex formwork, the need for removal - are compensated for on heaving soils by the absence of bending forces, cushions made of non-metallic materials, and excavation work. For monolithic grillages, bored piles are more often used. The beams of prefabricated grillages are often joined at the ends of the SHS.

The advantages of a hanging grillage are:

The disadvantage is the impossibility of making a floor on the ground - all other technologies (joists, slabs) are more expensive. When building a cottage using frame, log, or half-timbered technologies, the construction budget is always minimal. Therefore, the costs of removing and insulating communications underground cannot seriously increase the cost per square meter.

Underground grillage

The underground option is economically beneficial if the project includes a technical underground or a basement floor. The main advantage of a grillage over a strip foundation is its support on piles:

The gap under the sole of the monolithic structure in the ground is protected with sheet materials. This cannot be done for standard MZLF tape. Waterproofing and a drainage system can increase the service life of any reinforced concrete structure, therefore they are necessary for any low grillage.

Ground grillage

If the depth of the swelling layer in the building area is less than 12 m, it is more rational to use a low-type ground grillage. To compensate for heaving forces, it is enough to leave a 10 cm gap between the soil and the slab/tape. The gap is covered on both sides with sheet material to prevent soil from being packed into it or applied by storm drains.

In practice, the technology is produced in the following order:

The ribbon rising above the ground is also the base of the building. To ventilate the underground, vents in a monolithic structure are required. Therefore, it is recommended to increase the height of the grillage to 0.6 m in order to make vents no lower than 0.4 m from the zero level, otherwise in winter these holes will be clogged with snow.

Thus, a grillage on piles is in most cases preferable to other types of foundations in low-rise construction. The piles pass through heaving soils and rest on the bearing layer. The grillage collects operational and structural loads, distributing them evenly. There is no heaving silt at all, which guarantees the maximum possible service life of the building.

In climatic zones with a soil freezing depth of more than 2 m, as well as on unstable soils, laying a strip foundation is not practical. It turns out to be expensive and not durable enough. The optimal solution in such conditions is a pile foundation with a grillage.

What is a pile foundation with a grillage

This is a structure of several reinforced concrete beams, the lower parts of which are immersed below the soil freezing level, and the upper parts are united above the ground by a beam called a grillage. Pile foundations are erected for the construction of brick, block buildings, structures made of rolled metal, and other materials.

This type of foundation has significant advantages over the simpler, cheaper pile foundation without a grillage, which does not distribute the weight of the house evenly between all supports. Its use is limited only to wooden log houses, frame houses or frame extensions.

Possible options

The grillage is a support for the walls of the house. It takes the weight of the entire building structure, distributing it evenly between the buried beams. The following materials are used for its manufacture:

• tree;
• metal;
• reinforced concrete.

According to the type of execution, reinforced concrete beams are divided:

• low when located on the ground;
• high, in which they are located above the surface of the earth.

Piles

Piles are selected taking into account the load and type of soil. They are made of metal, reinforced concrete, and rarely of wood. According to the installation method they are divided into:

• driving;
• bored;
• reinforced concrete eyebrows;
• screw.

Drive beams are driven into the ground under the influence of impact load. For this, special equipment is often used.

When installing bored supports in a drilled well, formwork is arranged, metal reinforcement is installed, and it is filled with concrete. Ready-made reinforced concrete drill supports are driven into a pre-drilled well.

The screw bars are made of metal with a pointed end and have metal screw blades that easily cut the soil. They are screwed into the ground. To install screw supports to a depth of more than 2-3 m, special equipment is required.

Depending on the cross-sectional shape, they are divided into:

• round solid;
• round hollow;
• square;
• triangular;
• multifaceted;
• special complex sections.

According to the nature of load transfer, they are divided into:

• racks;
• hanging.

Hanging ones have a side surface that transfers the load to the ground. The side parts are made uneven, with protrusions. The beam seems to cling to the ground. They are used if the layer of unstable soil is very large or the groundwater is located high.

Possible accommodation

In the vast majority of cases, the support bars are positioned strictly vertically. If it is assumed that the load can act horizontally - for example, on inclined surfaces, then several beams in one place are installed inclined.

When installing the foundation, the piles are grouped as follows:

• single;
• in the form of pile strips - distributed along the length of the loads in one or several rows;
• in the form of pile bushes - several piles for each load-bearing support.

Arrangement for independent foundation design

When designing a pile-grillage foundation yourself, you should:

1. Draw a house plan to the selected scale.
2. Determine the location of the bookmark in the corners of the house.
3. Do the same at the intersections of walls and partitions, if the distance between them is more than 3 meters.
4. Plan intermediate supports at the same distance. This distance should also not exceed 3 meters.

Foundation calculation

After arranging the support beams and determining the total number, the area is calculated. To do this, you should follow the sequence:

Calculate the mass of the house. It is necessary to take into account the weight of all materials, roof, furniture, people who will be there.

According to the standards, taking into account the mass and safety factor, the supporting area is determined. It is calculated by dividing the mass of the house, multiplied by 1.4 (margin of safety), by the bearing capacity of the soil.

The total supporting area is divided by the number of beams, and the nearest larger area is selected according to the standard. If the calculated area of ​​the pile differs greatly from the nearest standard one, it is worth calculating the option by increasing the number of supports for the grillage with a smaller area of ​​each support.

Construction technology

The construction of the foundation begins when all the calculations are ready, the dimensions of the piles and grillage are selected, and their places on the plan are determined.

Marking the foundation on the ground

1. Remove the top layer of soil.
2. Using stakes and a cord, mark the outer boundary of the house.
3. Similarly, pull the cord along the inner border of the walls.
4. Check perpendicularity, parallelism of lines, equality of diagonals.
5. Mark the locations of future piles.
6. Excavation work, installation of support beams for grillage

The procedure for organizing excavation work depends on the type of piles. Screw ones are usually screwed in by hand, leaving heads of the same height above the ground, which can be conveniently checked using a horizontally stretched cord.

They drill wells and install assembled formwork. 4 reinforcements with a ribbed surface are lowered down and secured. The rods are pre-fastened together with wire or welding. To be fastened to the grillage, they must be 0.6-0.7 m above the ground surface. The formwork with reinforcement is poured with concrete.

Grillage installation

If the grillage is metal, rolled metal (channel, profile pipe) is welded to the protruding parts of the piles. You should strictly monitor the horizontal position. Otherwise, the load will be distributed unevenly, which will lead to the destruction of the building.

Installation of the low one begins with adding crushed stone in a layer of 0.15 m, compacting it with a vibrating platform. The crushed stone is not poured all at once, but sequentially in 3-4 steps, compacting each layer with a vibrating mechanism. Then the formwork is installed. Its width should be greater than the width of the wall. You can follow the standards for strip foundations. The height of the formwork is determined by the required height of the base.

For reinforcement, ribbed steel reinforcement is used. The upper and lower belts are fastened with rods of smaller diameter. Some of the ends of the reinforcement released from the piles are bent and attached to the upper chord, and some - to the lower chord. The length of the bent reinforcement must be at least fifty times the diameter of the rod.

Ventilation openings and structures for entering utilities are installed. After this, concrete is poured. A vibrator is used simultaneously with pouring. This operation is performed to increase the strength and uniformity of the concrete mass, which is then left to harden. The formwork can be removed after the concrete has gained at least half its strength. The duration of this process depends on the ambient temperature. At +20 ⁰C, four days are enough. At +10 ⁰С it takes up to two weeks. If the temperature is even lower, then heating of the concrete is necessary to harden and gain strength.

Advantages and disadvantages

Pile foundations with a grillage are popular due to their undeniable advantages:

1. Suitable for types of soil in which no other types of foundations provide strength: deep freezing of the soil, weak, heaving soils.
2. Provide stability and have high load-bearing capacity.
3. They can be laid on slopes.
4. It is possible to carry out work in winter.
5. Low cost of materials and work, cheap type of foundation.
6. The entire structure can be erected and concrete poured in a couple of days.
7. No careful preliminary preparation of the site is required.

In addition to its advantages, such a foundation has disadvantages:

It is necessary to insulate the structure due to the presence of space under the floor.

Cannot be used for massive structures.

Careful calculation of the foundation is necessary, since there is great uncertainty in the behavior of the soil.

In general, this is an excellent option for low-rise buildings, where speed and low cost of construction are valued, or where there is a need to build a building on slopes.

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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.

Due to the variety of construction technologies and materials used for pile-grillage foundations, there is a special terminology:

• base - a layer that absorbs vertical loads and lies below the freezing mark;
• pile - a vertical structure made in the soil or immersed in it;
• pile field - a group of piles for one structure, building;
• grillage - a monolithic or beam structure along the heads of piles (slab, lattice, frame or beam);
• low grillage – buried in the soil or located at the ground level;
• high (hanging) grillage – raised above ground level;
• bearing capacity of a pile is the sum of soil resistances on the side surfaces and under its lower end.

Based on material, bored piles are classified as follows:

• composite - reinforced concrete inside steel or polymer permanent formwork (large diameter pipe);
• rubble concrete - in the lower part of the pile stones are sunk into concrete (maximum size 15 cm, strength not lower than the design grade of concrete), the upper part (0.5 - 0.7 m) is filled with clean concrete, reinforcement is usually along the entire length (except for backfill);
• reinforced concrete - the pile is poured entirely from concrete with reinforcement along the entire length (usually not stressed);
• concrete - reinforcement only in the upper part for piping with a grillage.

The pile shaft can be manufactured in several ways, even using the same materials. For example, if a hole in the ground with a reinforcement cage placed inside is filled with concrete, the pile will be shellless.

Scheme of a pile with expansion - TISE.

If the pile reaches the bearing layer, is poured into a polymer or metal pipe, which does not carry loads and remains in the well for the entire period of operation (non-removable), acting as waterproofing, a pile with a shell is obtained.

If the temporary formwork is removed after pouring, the pile is called a temporary shell, the method is a vertically moved VPT pipe. If the formwork remains inside the well and performs load-bearing functions, the pile is called a pipe-concrete pile.

To increase the load-bearing capacity, the base of the pile can be widened with a monolithic base. The base is drilled out with a special tool, an explosion or concrete piles. In a general grillage, the head of a bored pile can have a sliding mate or a rigid embedment into a monolith.

If, during geological exploration of the site, the occurrence of a bearing layer deeper than 3 m is revealed, bored piles-racks will cost an individual developer more than a screw foundation SVF or a floating slab. In this case, suspended piles are more effective, the bearing capacity of which depends on the density and porosity of the soil. If the frictional forces on the side surfaces are not enough, other foundation options should be considered.

Unlike a strip foundation, the depth of the grillage does not depend in any way on the characteristics of the soil:

• the tape rests on the ground with its sole, there are lateral shear loads from heaving forces;
• The grillage does not rest on the ground, it is created solely for tying piles, distributing loads, and supporting wall materials (especially important for foam blocks and bricks).

After pouring the monolithic grillage, an air layer is created between the soil and its base to compensate for heaving forces. In low grillages, it is protected on the sides with sheet materials to prevent the soil from shedding and filling this space with heaving soil.

Taking into account the above, a monolithic grillage along the heads of bored piles is effective in the following cases:

• lightweight buildings - budget savings of 30 - 50% in comparison with a slab, strip foundation for log houses, half-timbered, frame, panel (SIP technology), panel cottages;
• complex terrain - slopes with a height difference of more than 1.5 m in the building area;
• high groundwater level - piles can be poured into the shell with a slight rise in water or by temporarily pumping it out of the well;
• swamp, coastal zone - excavation work for other types of foundations is impossible.

Piles are economically effective in individual construction only at a depth of 3–5 m, which is usually sufficient for lightweight structures. With normal geology on flat areas, piles reduce the construction budget of brick and concrete buildings by half. Only in this case does the foundation comply with the requirements of SP 24.1333, which regulate the design of pile foundations.

Step-by-step instructions using the example of a monolithic grillage on bored piles

To build a foundation of this type, an individual developer needs to determine the main dimensions of the elements: cross-section of the grillage (height, width), depth of the well, parameters of the reinforced belt, type of formwork. After which, the amount of building materials is calculated. For convenience, below are step-by-step instructions describing the key points.

Geological surveys, calculation of parameters

Unlike screw piles, for which it is often enough to test screw in a building spot in several places to determine the depth of the bearing layer, this will require full-fledged geological surveys. According to SP 24.1333, this will require a set of operations:

• soil testing with static loads;
• pessiometry, dynamic and static probing;
• laboratory analysis of groundwater, soils from different layers during drilling 3 m below the design level.

In addition, specialists will take into account the impact of piles on nearby buildings and the environment. The result of the research is a geological section in which the thickness of each layer of the layers of different rocks present in the building area is visible. This allows you to select from the corresponding SP tables the standard values ​​of the bearing capacity of clay, sand, and loam to calculate the bearing capacity of the pile.

For example, for soil conditions of 2 m refractory loam, 1 m hard loam, on top of wet sand, there are several options for drilled piles:

• A – the depth of the piles is more than 3 m (passing through loam with the base resting on the sand), diameter 0.5 m;
• B – depth 3 m, diameter 0.4 m;
• B – depth 2 m, diameter 0.5 m.

For reinforcement, rods of 10–12 mm of periodic section are used. The clamps are bent from 6–8 mm of smooth reinforcement. For tying, it is better to use annealed wire. The pitch of the horizontal clamps is 30 - 60 cm, the rods should protrude 30 - 40 cm above the heads. After stripping, they are bent at right angles parallel to the axes of the walls and connected to the lower belt of the grillage.

Pouring and waterproofing

The formwork for the grillage begins to assemble from below.

Due to the large volumes of concrete work, a pile-grillage foundation is usually poured in stages. First, the mixture is placed in pile formwork and compacted with an in-depth vibrator or reinforcing bars to remove air. The grillage formwork is installed after the piles have gained at least 50% strength (3 – 5 days after pouring). The technology looks like:

• deck installation - only for a hanging grillage, holes are cut in the shield according to the size of the piles, it is put on the heads, supported by H-shaped posts along the entire length;
• installation of side panels - attached to the deck, propped up with bars or pins, the top side should be 5 - 7 cm higher than the design mark;
• reinforcement - two belts of 10-16 mm bars of periodic cross-section reinforcement, fastened with 6-8 mm clamps, bend at the corners, at the junction of the walls.

Grillage reinforcement.

Filling occurs according to standard technology with laying and vibration compaction of the mixture. The entire formwork must be filled in one go. Caring for concrete consists of protecting it from waterlogging (covering it with a film from rain), drying out (sand or sawdust on the top edge of the grillage with periodic moistening in the first three days).

This is done after stripping the grillage in several ways:

• impregnation with penetrating compounds (the service life is similar to concrete structures, no repairs are required);
• coating with bitumen mastics (resource 15 – 30 years, budget option);
• gluing with roll materials (lifespan of glass hydroisol is 30 - 50 years, the need to seal joints, use 2 - 3 layers).

Preferable impregnation waterproofing or a set of measures according to the last two options (coating + gluing).

Blind area and storm drain

For any foundation, regardless of its design, a blind area is required that has a 4–7 degree slope from the building outward. This structural element allows rain and melt water to be drained away from concrete structures under a monolithic low grillage and under a high grillage. To prevent runoff from destroying the soil adjacent to the blind area (usually the fertile layer), stormwater inlets (receive water from the roof drain) and trays that transport liquid to a separate underground reservoir are integrated into its outer perimeter.

To reduce the heaving forces under the monolithic grillage, which exert pull-out loads on the piles, at a depth of 40–70 cm. To do this, extruded XPS polystyrene foam is laid at the bottom of the trench. The width of the blind area should be 5–10 cm larger than the projections of the roof slopes, so that when the roof gutters overflow, the water does not destroy the fertile layer.

The standards SP 71.13330 of 2011 recommend a blind area width of 0.7 - 1 m for sandy, clayey soils, respectively, with a tight connection to the backfill (false base) of the pile-grillage foundation. It is made of waterproof material:

• concrete screed 5 cm thick in the thinnest areas;
• paving slabs/paving stones;
• rubber or PVC tiles;
• composite decking.

A budget option is a blind area made from dry asphalt concrete mixtures, used for repairing roadways and lining garden paths. It is compacted with a tamper, does not require heating or melting, and increases strength over time.

Following the recommendations given, even an individual developer without special education will be able to produce a pile foundation with a monolithic grillage with a minimum budget without errors. When properly calculated, the service life of underground structures is not inferior to other types of foundations, maintaining high maintainability and the possibility of increasing the usable area during operation.

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 a grillage is to combine piles into a single structure, which significantly improves load distribution, prevents subsidence of individual piles into the ground, and reduces the risk of damage to load-bearing walls and other structural components of the structure.

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 in the construction of low-rise buildings, when a more durable foundation 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 a strip or monolithic foundation is 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 required 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 starting the construction of a pile foundation with a grillage, preparatory work should be carried out. 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 to build a frame house measuring 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 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 a 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:

1. Using special equipment, wells are drilled into the ground to a depth of 80–100 cm. The diameter of the well depends on the total weight of the structure and the cross-section of the nozzle used. If necessary, the well can be expanded using a regular shovel.

   Before pouring the concrete mixture into the well, a reinforcing frame is installed

2. The inner walls of each well are lined with 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.
3. 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

4. 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. The upper part of the frame must extend 15–20 cm from the well. This is necessary for its further connection with the grillage.
5. After all the preparatory steps, the concrete mixture is poured. For this purpose, concrete grade M500 from the manufacturer is used. 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 a wooden batten. 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 grillage level.

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.

Ventilations 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:

1. 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.
2. 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 bars of the reinforcement cage

3. 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 the inner surface of the formwork are insulated with roofing felt.
4. 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 grillage be completely filled 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

5. 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.