Pile-grillage(or columnar-ribbon, both names are equivalent) the foundation is a structure consisting of pillars immersed in the soil and connecting them above the surface of the ground with reinforced concrete, wooden or metal tape. The peculiarity of this type of foundation is that they can be installed on any soil except rocky ones. SRF may vary in construction technology, material of manufacture and design features of piles.
Piles - types and features
According to the material of manufacture, reinforced concrete, wooden and metal piles are distinguished:
Wooden They are used mainly for the construction of buildings from the same material, often these are outbuildings, gazebos, and bathhouses. For the construction of residential premises, more durable foundations are usually installed. Installation can be done either singly or in groups of 3-4 pillars in a bundle to increase strength and load-bearing capacity.
Metal piles can be driven or screwed, but the second option is more common. A screw pile post is a metal pipe, the immersed end of which is made in the form of a cone with a screw blade for screwing. The cone-shaped tip can be cast or welded. Cast piles are more reliable and durable, since they do not have a welded seam, the strength of which is reduced. The steel product must be treated with an anti-corrosion coating, and during the installation process the pipe cavity is filled with concrete. The service life of such a foundation can reach up to 400 years.
Read more about types, types and features technologies of pile foundations.
Reinforced concrete piles are made from reinforced concrete, at the enterprise (drived) or directly on site (rammed).
DIY pile-grillage foundation
Step 1 - Soil Study
The purpose of the geological study of the site is to determine the type of soil, its bearing capacity, degree of heaving, level of occurrence groundwater etc. The choice of foundation and the features of its construction depend on these characteristics.
For a full analysis, you should contact specialists, since independently drawn conclusions may turn out to be erroneous, which will affect the quality of the foundation itself and the building as a whole. Especially it concerns columnar foundations, since it is not possible to thoroughly check the soil layers, reaching the level of solid soil. To conduct research, you can contact a geodetic company or send soil samples to a laboratory.
If for some reason this is not possible, then the type of soil should be determined.
Types of soil and their characteristics.
- Sandy soil. It has good drainage properties, does not heave and compacts tightly. Foundations on such soils are easy to construct and durable.
- Fine sandy. It has increased buoyancy and a tendency to swell. It is not recommended to build foundations on such soils, but in the case of pile-grillage foundations, the main thing is to carry out installation work in accordance with all requirements.
- Clay. Clay soils are prone to severe swelling. To build a foundation, an anti-heaving cushion is required.
- Rocky and clastic soils. They are difficult to work with, but they have no equal in reliability. The rock does not freeze, is not subject to swelling and buoyancy. However, this is the only type of soil that is not suitable for the construction of pile foundations.
Step 2 - Carrying out calculations
Step 3 - Site Preparation
- Produced area cleaning.
- Determined location of the future foundation. It is important that the remaining buildings on the site are located at least 3 meters from the construction site. You should also choose an area free of tree rhizomes and stumps, as they make it difficult to drive the piles.
- The turf layer is removed under future construction, and the soil surface is leveled.
Step 4 - Marking
- To a cleared and level area from the drawings the layout is being transferred buildings - first, use pegs to mark the outer corners, then the intersections of the walls. Piles will subsequently be installed at these points.
- Then between the pegs the fishing line is stretched or twine, thereby denoting foundation installation line.
- Along the perimeter of the stretched twine there are marks places for installing additional piles. They should be located approximately 2 meters from each other.
It is important to make the markings accurate. Permissible deviation – 2 cm.
Step 5 - Installation of piles
Immersion of hammers and screw piles carried out using the necessary equipment or devices.
Installation of bored piles consists of several stages:
- Held well drilling below soil freezing by at least 0.5 meters.
- If it is necessary to strengthen or drain the load-bearing soil layer, sand cushion is being installed.
- Into the well fits asbestos cement pipe , the upper part of which should protrude above the surface to the height of the grillage. If this is a hanging option, then the length of the protrusion is about half a meter on a flat surface. If the landscape is sloping, then the length of the ground part varies.
- Then, using a level, it is made horizontal control And pipes are cut to the required level.
- After that the pile is being reinforced, most often using reinforcement with three or more (depending on the diameter of the piles) rods. For increasing strength, the vertical frame is pulled horizontal jumpers at a distance of approximately 0.5 meters.
- The fittings are located in such a way that it top part performed above fill level slightly lower than the height of the grillage.
- After this, using a gas pump or manually (in private construction) Concrete is poured inside the pipe. In some cases, concreting of piles is carried out along with pouring the grillage.
Step 6 — Arranging the formwork and pouring the grillage
Applicable only to poured reinforced concrete foundations.
- For installation of hanging type strapping under formwork a layer of sand is poured, the so-called sand cushion. It serves to maintain and stabilize the form for pouring concrete and raising the grillage above the ground.
- Formwork being constructed from wooden planks and is a rectangular trench for subsequent pouring concrete, which connects all the piles of the structure with one tape. The formwork must be constructed in such a way that grillage tape was wider than the walls future the buildings by 5-10 cm.
- The formwork is being installed at a distance of 20 cm from the ground level for hanging grillages and 20-30 cm below the level for shallow ones.
- At erection of formwork, Special attention is given to its fixation. The immobility of the form for concreting is the key to a high-quality grillage tape and clear geometry of the structure. The fixing spacers should be located at a distance of approximately 0.8 meters from each other.
- Inside the formwork a reinforcing frame is placed which is necessary connect to the pile frame knitting wire. It is also important to make the correct bends of the reinforcing bars at turns - they must be made at right angles.
- Reinforcing frame should be located at least 3 cm from the walls and bottom of the formwork, so that when pouring it will be completely concreted.
- Horizontally located along the perimeter the rods are tied with tying wire for greater durability.
- Then it is produced pouring concrete form using a concrete pump.
- To distribute the mixture as evenly as possible, parallel to pouring, a deep vibrator is used. The principle is as follows: 1-2 people direct a stream of concrete into the formwork, and the third assistant distributes just arrived mixture using a vibrator.
- When the concrete will harden(usually it takes 2-3 weeks) the formwork is removed, A sand cushion is removed.
- IN hot dry weather, to avoid cracking, throughout the entire drying period grillage necessary moisten with water.
For self-preparing concrete mixture You will need to mix (proportions are indicated by weight):
- cement(M400) – 1 part;
- sand– 2.8 parts;
- aggregate(crushed stone) – 4.8 parts;
- water– is added in such quantity that the mixture turns out to be elastic and of medium viscosity.
From a mixture of ingredients in such proportions, concrete grade M200 is obtained.
The binding of metal piles is carried out using an I-beam or channel beam by welding. A wooden grillage is usually used for houses made of wood; in this case, a metal pin is placed in the pile post, with the help of which a transverse wooden beam is fastened.
Common mistakes
- Lack of space between the grillage and the ground. This happens if you don't delete it. sand cushion. In this case, the foundation will be be under pressure during soil freezing, which can lead to its deformation.
- Imprecise definition soil bearing capacity. Result - incorrect calculations, instability and immersion of the foundation into the ground.
- Insufficiently deep immersion of piles. If the piles are located at the freezing level, then in winter period pressure on the poles may intensify to such an extent that supports Just will tear.
What determines the cost of SRF?
The price of a pile-grillage foundation is determined by a combination of several factors:
- Number of piles and them characteristics– material of manufacture, diameter, length.
- Difficulty level works For example, a foundation with a suspended grillage will cost less than one with a recessed grillage, since the latter option involves excavation.
- Installation method piles If screw piles can be installed independently, then for driven piles it is necessary attract equipment.
- Dimensions being built foundation.
- Quantity additional material– sand, cement, formwork, etc.
On average, 1 m 2 of grillage strip requires 350 kg of cement, 1000 kg of sand and crushed stone and 8 meters of reinforcement. The approximate cost of construction, taking into account the work, is from 2000 to 3000 rubles.
The price of some construction companies for the construction of a driven or bored foundation can reach 4000 rubles.
In contact with
Grillage strip foundation represents a reliable and durable support for the structure. Two technologies are used to create it. One is necessary to create a foundation located above ground level. The second technology is the creation of a grillage that takes on part of the load.
The foundation is suitable for laying on uneven surfaces, slopes, and areas with difficult terrain. With it, achieving a horizontal surface is much easier than with other types of building foundations. A strip foundation does not require complex preparatory work to level the site and the use of special equipment. This gives an important advantage - low cost.
According to the structure, the grillage strip foundation is divided into several types:
- High. Installed above ground level at a distance of 15 cm. Suitable for areas with frozen ground with periodic swelling of the soil. After the construction of the building, it is necessary to insulate the floors of the first floor.
- Elevated. It is laid at the level of the ground cover. To relieve pressure from the grillage, it is necessary to remove part of the soil.
A strip foundation requires careful calculations of the thickness of the grillage, the number of piles and other parameters.
When choosing a grillage strip base when building a house, two basic rules must be observed:
- Creating a sand cushion. Its thickness is 20-30 cm, it is laid under piles and a concrete frame in order to protect it from destruction under the influence of soil.
- Creation of waterproofing of supports and grillage. For this purpose, roofing felt sheets are used, asbestos cement pipes or plastic film.
The foundation is suitable for the construction of buildings from lightweight materials.
Pros and cons of the design
Scheme pile foundation with grillage
Strip foundation has advantages:
- low cost;
- reliability;
- the ability to equip a basement or cellar;
- distributes the load evenly over the base;
- suitable for structures made of any materials;
- does not require removal of soil throughout the entire base area.
The grillage improves the quality of the strip foundation, makes it stronger, and increases its service life.
There are fewer disadvantages, but they still exist:
- cannot be installed on soils with weak bearing capacity;
- requires labor-intensive work.
What is the tape design?
One type of foundation with a grillage
When constructing a grillage strip foundation, several types are used building materials what influences the name finished design. The differences lie in the manufacturing technology of the base.
- Monolithic. Work on creating the structure is carried out at the construction site. A monolithic foundation consists of concrete and reinforcing mesh. To create it, formwork is constructed in a dug pit, then reinforcement is laid. The resulting structure is filled with concrete mixture. The advantage of a monolithic base is durability - it can last 100 years or more. The use of a monolithic strip foundation is relevant in the construction of structures planned for long-term operation. The design requires 4 weeks to assemble.
- Precast concrete. The structure is assembled from reinforced concrete blocks cast at the factory. The elements are connected to each other by reinforcement, the resulting gaps are filled with concrete mortar. Prefabricated strip structure suitable for frame houses. The service life of the base is 50-80 years. But it cannot be used on subsiding and heaving soils.
- Rubble. Made from rubble natural stone. They require adherence to the technique of laying elements, correct calculation and connection. If the masonry technology is violated, the house may crack. Life time rubble foundation is 50-70 years.
- Brick. A foundation that is in little demand and requires labor-intensive and time-consuming work. The structure is constructed from bricks or building blocks. The foundation is short-lived: if the installation technique is followed, the service life is no more than 50 years.
The importance of grillage in building construction
Section of a strip foundation with a grillage
The grillage performs 2 main functions:
- Distribution of longitudinal and transverse loads along the perimeter of the foundation.
- Combining structural elements of the base into a monolithic structure.
The functionality of the grillage depends on the material of manufacture. The element is classified into several types:
- wooden - made from beams, it is cheap, accessible and easy to install. Suitable for houses built on wood. Short-lived, subject to rotting and rapid deterioration;
- steel - is a beam frame built from steel rods and metal piles. It is used in the construction of bathhouses, one-story houses, and change houses. Subject to corrosion, requires additional processing before use, but reliable and durable;
- monolithic - the grillage is made in the form of a system consisting of beam floors and vertical elements connected by concrete into a single structure. It is distinguished by its endurance, resistance to external influences, reliability and durability.
The grillage increases the service life of the foundation, protects it from excess load, preventing premature destruction of the foundation.
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
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.
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 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.
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, the pile-grillage foundation is more stable. Although main drawback pile foundations remain: 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.
Construction of a pile-strip foundation (to enlarge the size of the picture, right-click on it)
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 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. They can have a round or square cross-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 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:
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 to a larger 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 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 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, 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.
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).
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). 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.
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 during the construction of 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.
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. Last step at this stage - pouring 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 selected, it is welded to the pile heads. When working, it is important to maintain strict horizontality: then the load will be transferred evenly.
For recessed device 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 Communication(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.
The only drawback that a pile-grillage foundation has is the complex design of the basement floor. In 99% of cases, employees of specialized companies will state that a basement is impossible in this case. In practice, such buildings have solid operating experience in all regions of the Russian Federation. However, not every designer will be able to calculate piles and grillage.
The advantages are that there are no restrictions on the terrain and geology of the site. Two-story brick buildings can be supported on a monolithic grillage along the pile heads. The disadvantages of the design are expressed in the insufficient qualifications of specialists. It is extremely difficult to perform calculations on your own without a specialized education.
The design principle of any foundation is to ensure load-bearing capacity and reduce heaving forces. In other words, if you place a building on loose soil, it will sink into the ground, and uneven swelling will tilt it to one side, making operation impossible.
The first problem is solved by passing through bulk or unstable soil horizons and placing the base of the foundation on a layer with sufficient bearing capacity. There are several ways to get rid of heaving forces:
- excavation of soil for replacement with non-metallic material compacted in layers (backfilling of boreholes or pits);
- preservation of geothermal heat from the subsoil under the building (insulation under the base of the foundation, side blind area and the entire height of the foundation, from the base to the top of the base with continuation to the walls);
- drainage of the perimeter of the cottage (ring drainage + storm drainage in the blind area).
The default disadvantages of any of these methods are that the construction budget increases.
If you choose a deep strip foundation, you will have to drill wells below the freezing mark and purchase several dump trucks of sand for backfilling and cushions. When pouring a slab with a maximum supporting surface, you will have to order several mixers and spend money on a huge amount of fittings.
Piles are free from most of these disadvantages by default:
- they are immersed below the freezing mark, to the level of the bearing layer;
- the load-bearing capacity is increased by lateral friction forces;
- the pulling forces of heaving soils for small-diameter cylinders are much less than for a strip or slab;
- the strip foundation along their heads, called a grillage, absorbs structural and operational loads from the building, evenly distributing them onto the pile field.
Thus, with normal stability, the pile-grillage foundation experiences almost no heaving and overturning forces and has a reserve of bearing capacity.
Piles have the following advantages:
- low construction budget - the minimum possible for screw piles, slightly more expensive for bored modifications of piles;
- construction time - the productivity of driving screw piles is 20 - 30 per shift, bored piles are 1.5 times lower, which is an order of magnitude higher than any other technology;
- landscape – for elephant cottages and swampy areas this is practically the only solution;
- geology - when choosing these technologies, geological surveys can be omitted (savings of 30 thousand rubles), replacing them with trial screwing of screw piles in the building area;
- groundwater level (GWL) – there are no restrictions at all, piers and houses can hang over the water;
- maintainability – 100%, all other foundations are restored using screw piles.
Foundation on bored piles with reinforced concrete grillage
Even taking into account the incompetence of construction company employees, the disadvantages cannot outweigh the indicated advantages of pile foundations. The main disadvantages are the absence of a basement floor and the need to decorate the underground with a fence. However, both of them are very controversial - budget vinyl siding is enough to get it. The construction budget is slightly increased by the need for thermal insulation of communications inside the underground, in the ground to the freezing mark.
Application area
Piles are a budget solution for small architectural forms (SAFs), outbuildings and fences. Selection of strip foundation (grillage) on bored or screw structures economically justified in the following cases:
- high ground level - the grillage is raised above the ground, heaving forces are practically absent, the piles rest on the bearing layer;
- wooden houses - the optimal solution is a pile-screw foundation with a grillage made of channel bars;
- brick, foam, aerated concrete walls - bored piles with a monolithic grillage can withstand the prefabricated loads of two-story mansions.
Many individual developers confuse a strip foundation on piles with a grillage. While externally similar, the grillage rests on the pile heads and has no contact with the ground. It serves solely to redistribute loads. The tape rests completely on the ground; the piles only enhance the load-bearing capacity when the load-bearing capacity of the upper soils is insufficient.
A pile-grillage foundation is the only solution for operating conditions:
- coastal zone - unlike a strip foundation, there is no need to tear off trenches or pump out water;
- hilly area - if the height difference is more than 2 m in the building area, a strip foundation or slab will be too expensive, the pillars will be knocked over by heaving forces.
Piles are used in the repair of strip, slab and columnar foundations of frame, log, panel and panel houses. Thus, the advantages of spatial structures with rigidly fixed beams at the heads of bored or screw piles outweigh the disadvantages.
In addition, the shortcomings indicated in the aggressive advertising of opponents of pile-screw foundations are not justified and not supported by facts. During the Soviet era, screw piles coated with hot zinc were produced for the needs of the army. Buildings on these pile fields are currently being exploited, so the actual resource is still unknown.
Screw and bored piles: what are the differences
In individual construction, the greatest demand is for bored and screw piles, which can be manufactured and installed independently. The definition of bored is not entirely correct for the technologies used; this is how the structure is concreted into a hole drilled rather than pressed into the ground. The correct name in this case is a drilled pile.
Despite the similarity in design, there are still differences:
- the disadvantages of bored (drilled) piles are the increase in labor costs; even with a motorized drill, it is very difficult to make a 3 m deep well with a diameter of 40 - 50 cm;
- a pile-grillage foundation on screw piles is installed in 3–7 days, depending on the grillage material (rolled metal, monolith, respectively).
Foundation on screw piles
Disadvantages of bored piles - limited depth of 3 - 5 m well during operation hand tools, do not allow the use of this technology in bulk, man-made, and mined areas. There are no such restrictions for pile-screw foundations:
- it is enough to increase the construction budget by 5 - 7 thousand to purchase an electric drill and a multiplier in order to mechanize the screwing process;
- Productivity does not increase much, but workers are freed up and diving accuracy increases.
The main problem when choosing pile-screw foundation What remains is the search for a manufacturer of quality products. In most regions of the Russian Federation, companies produce low-quality screw piles, offering piles made from thin-walled, used or seamed pipes. The blades have different angles and propeller pitches; they start not from the lower third of the peak, but from the body of the pile itself.
Therefore, experts recommend choosing piles with cast tips made from seamless pipe. If the anti-corrosion treatment is unsatisfactory, the piles can be painted with special compounds even in a building spot. This will ensure maximum service life of the foundation and maintainability of the pile field.
When manufacturing a monolithic grillage using screw piles, it is necessary to qualitatively connect foundation elements from different materials:
- holes are burned in the body of the pile at the level of the grillage reinforcement belts;
- reinforcement is inserted into them and connected to the rods of a horizontal reinforced concrete beam.
The home craftsman usually does not have any problems with embedding the heads of bored piles into a monolithic grillage. Both technologies are extremely simple; no insulation is required. However, the drainage around the building and the blind area with a sealed junction with the underground intake of the pile structure still remain a necessary condition normal operation.
Thus, the disadvantages of pile-grillage foundations lie mainly in the absence of a basement and the complexity of design (calculations). The advantages surpass all other types of foundations.
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Under certain conditions, the construction of a pile foundation becomes advantageous. The pros and cons of this design make it ideal for a private home on difficult soils.
The installation of a pile-grillage foundation requires, in most cases, lower costs. This is due to a decrease in the volume of earthworks. Before making piles, you need to study their advantages and disadvantages, scope of application, description of the technology.
Types of piles
There are several ways to make such a pile-grillage foundation. The pros and cons in this case will depend on the technology and materials used.
Based on material, supports are divided into:
- wooden;
- reinforced concrete;
- metal.
The former are rarely used, since their main disadvantage is low durability. Wood is destroyed by moisture, rot, and microorganisms.
Reinforced concrete piles have high load-bearing capacity. Typically, the laying depth for your home is 1.5-3 m. The cross-sectional dimensions are chosen depending on the characteristics of the soil on the site.
Metal supports for pile foundations are an option for private housing construction. They are not designed for high loads, so they are used for wooden or frame buildings.
The following classification is carried out depending on the technology of immersion of elements. Installation of a pile foundation can be done in three ways:
- driving;
- bored;
- screw.
To make a pile-grillage foundation with your own hands, the driving method is not always suitable. It allows the construction of powerful structures, but has a significant drawback - the need for special equipment (heavy duty, pile drivers). Another disadvantage of a pile-rammed foundation is its strong impact on the surrounding buildings. When the mechanisms operate, shock impacts occur on the ground, which can cause damage to nearby buildings.
Pouring concrete
Pile foundation technology involves the use of concrete of classes B15-B20, depending on the load. It is not economically profitable to use a material with greater strength. You can make concrete yourself or order it from a factory. The second option is preferable, since in this case you can be sure that the resulting mixture has a certain strength. When mixing concrete by hand, be sure to study the manual for this process. Usually instructions are on the cement package.
Piles should preferably be poured in one go. Interruptions in the production of one element will lead to its weakening. Concrete pouring is recommended to be done at an outside temperature of 15-25 degrees Celsius. In this case, the concrete will gain strength faster and be durable. After every 30-50 cm of filling in height, a short break is taken, during which the solution is compacted with a vibrator or bayonet.
It takes an average of 4 weeks for the material to harden. In rainy and cold weather it takes longer. You can make a monolithic grillage after the concrete has gained 50-70% of its strength.
DIY screw pile foundation step by step instructions
Do-it-yourself pile-strip foundations are easy to do this way. The work is carried out in this order:
- clearing the site and preparing building materials;
- marking the area for the building;
- screwing piles using a manual or mechanized drill to the required depth;
- cutting off the supports one level at a time, at which the grillage on piles will be located;
- filling pipes with class B15 concrete;
- installation of a grillage on pile foundations.
Grillage options for screw piles In this case, building a pile foundation with your own hands does not require time for the concrete to gain strength. The next stage of work can begin immediately.
Strip foundation on piles
A pile-strip foundation is a structure of separate supports rigidly connected to each other. The grillage prevents the structure from settling unevenly. The tape can be made from:
- wood (only for a wooden or frame house);
- metal;
- reinforced concrete.
Each strip foundation has its pros and cons. When choosing a material for a strip foundation with piles, you should pay attention to the material of the supports and walls of the building. For wooden house- wooden grillage. For metal piles, it is reasonable to make a structure from rolled metal or wood, for reinforced concrete piles - from concrete.
The strapping completes the column-and-strip foundation. First of all, the depth of the grillage is determined. He can be:
- buried;
- ground;
- hanging.
The choice largely depends on the characteristics of the soil. Particular attention should be paid to the columnar-strip foundation with your own hands on heaving soil. In this case, there is a high probability of damage to the structure due to frost heaving. The grillage should not come into contact with the soil. Use two methods:
- hanging strapping (for this, 10-15 cm of sand is poured onto the ground, an element is poured over it, after which the bulk material is removed);
- recessed trim with low-density foam pad.
The construction of a pile foundation and a monolithic grillage is not very complicated. Provided the calculations are carried out correctly and the technology is followed, even a non-professional can handle the work.