Foundation plate on screw piles. Monolithic slab on piles

The choice and construction of the foundation always remains the most difficult stage in the construction of a building.

If the construction site is in a lowland, and in addition to clay soil, the freezing depth goes beyond the standard 120-130 cm, it is better to use a pile foundation. But for non-rigid foam concrete, gas-filled or wood concrete walls, the foundation must be tied with an excessively thick and powerful reinforced concrete grillage. Laying a monolithic slab will cost much more, despite the fact that there are practically no special advantages in comparison with the pile type.

The best option would be a pile foundation with a monolithic slab or a solid grillage.

It is always necessary to find a compromise between the efficiency and cost of the solution used. In this case, the advantages of a structure that uses piled supports and a reinforced slab are obvious:

slab foundation

Pile foundations, even with a large thickness of the strip grillage, could provide the necessary rigidity in the horizontal plane only due to the very large depth and strength of the supports. Any movement of the ground led to the deformation of the building box, especially if it was a bar or aerated concrete block. A monolithic slab of a pile foundation reinforced with a bar makes it possible to exclude even a hint of such a situation.

Construction of pile foundations with monolithic slabs

When arranging this type of foundation, the same technological methods are used as in the construction of a conventional pile-strip foundation, but taking into account the requirements for the formation of a grillage in the form of a monolithic reinforced concrete slab:

At the first stage, in accordance with the plan for the location of the bearing walls, wells are beaten for the required number of pile supports, waterproofing and reinforcement are laid in the body of the future pile; The area under the foundation of the house is compacted, covered with sand and gravel with drainage laid. Waterproofing and insulation are laid; Formwork is installed, the working volume of the grillage and slab is filled with reinforcement, the bar is tied up at intersections and layers, concrete is poured.

Soil preparation for the arrangement of a monolithic pile foundation

At the first stage, it will be necessary to plan and prepare the surface of the site in the same way as it is done in most cases for a thin slab foundation.

The entire fertile layer and surface loam are removed to the depth of the bayonet of a shovel, the bottom is carefully leveled and rammed with filling with a thin layer of coarse gravel. Despite the fact that the monolithic foundation slab will not rest on the bottom, it is necessary to strengthen it in order to maintain integrity with possible heaving. Along the perimeter of the foundation, a drainage pipe is laid in a trench to a depth of 70-80 cm, preferably on concrete preparation, but it is also possible on a sand cushion.

Before backfilling on the plan, it is necessary to punch wells for the required number of bored piles. Most often, these are TISE piles or anchor supports, with a cone-shaped widening of the sole.

Only after laying the waterproofing in the form of a roofing material or isospan pipe, the surface is covered with a thick layer of sand and carefully compacted in four or five passes. Thus, the soil under the future monolithic slab will be dry and relatively resistant to movement. If desired, a geotextile fabric of the type of dornite or similar density can be laid under the sand. In this case, the edges of the panels overlap by 15-20 cm.

Laying thermal insulation and fittings

A layer of waterproofing is laid on a leveled and compacted "gerbil", then a layer of extruded PPS, 100-150 mm thick. It is recommended to use thin, 30 mm thick heat insulator plates laid with seams between layers.

The insulation must be laid out over the entire surface of the foundation, at the places where the piles are installed, windows are cut out for supports, the laid waterproofing sheet is extended beyond the contour of the pile foundation and fixed on the formwork with a stapler. As a result, under the central slab and in the space between the pile supports there will be a thick layer of XPS, which will play the role of the bottom part of the formwork and further protect the entire structure from swollen soil. Formwork is installed along the contour of the monolithic slab.

Steel reinforcement with a bar diameter of 8 mm is used as a reinforcing element.

The lower layer of reinforcement is laid at a height of 30 mm from the insulation and is necessarily tied up with the reinforcement of the pile supports. The top layer of reinforcement is hung out so that the distance from the future surface of the monolithic slab is at least 40 mm. The reinforcement window is 25 cm, the step of dressing the upper and lower layers of the reinforcement is maintained at 70 cm.

Pouring concrete and arranging the blind area

After laying the reinforcing elements of the pile foundation, the procedure for pouring concrete into the shape of the pile foundation is started. The most competent will be to pour the entire array at the same time using a concrete pump and concrete mixers. To prepare 20-25 cubic meters of concrete for pouring within 12 hours of daylight hours is clearly beyond the power of even a team of workers, so it’s easier to buy it at the factory, but with the obligatory coordination of an exact delivery schedule.

At the first stage, the perimeter of the slab and the areas in which the external and internal pile supports are located are poured. The cavity inside each pile must be compacted with a vibrator with a maximum load, after which the concrete is cast along the contour of the foundation.

After 5-6 hours, the viscosity of the concrete will be sufficient to start leveling and trimming the surface of the monolithic slab. In the simplest case, the foundation mirror on piles can be leveled with a long rail, but a higher quality concrete screed is obtained using a specialized motor tool with a horizon machine.

After 6-7 days, the formwork is removed, and you can begin to equip the foundation blind area. Level 20-25 cm around the perimeter foundation slab backfilled with sand, waterproofing is laid and insulated with slab polystyrene foam.

A concrete screed is made from above with a slope of 5-6o. This is enough to remove water, but at the same time not create discomfort when walking. A properly planned blind area allows you to completely close the insulation layer, peeking out in the space between the piles.

Conclusion

Today, the foundation in the form of a monolithic slab - grillage on pile supports is the most successful for use on heaving soils. From the point of view of manufacturability and cost, a monolithic grillage foundation is the best solution, which is confirmed by the high popularity of monolithic systems in the northern regions of the country. The high resistance to heaving is evidenced by the fact that simple insulation of the blind area allows wintering the foundation slab, loaded only with the walls of the first floor, without the slightest trace of deformation or cracking.

Screw piles are successfully used in the construction of buildings on problematic soils (quicksand, heaving, deeply freezing and water-filled soils).

In this article - the technology of the floor device, types of plates for the technological stage of construction work.

Types and purposes

Ceiling - a structure that divides the building vertically (usually the ceiling is arranged above the technical underground and between floors). Floor slabs perceive loads from the weight of building elements, furniture, people in the house, and then transfer these loads to the walls of the building.

Overlappings are usually subdivided according to their location:

Underground (basement) - these structures serve to protect the building from the external environment (when building a house on screw foundations), as well as to separate it from the basement, basement or technical underground. Interfloor - these floors are arranged between the floors of the building during the construction of an object of several floors. Attic - necessary in the construction of buildings with attic and attic, their purpose is to separate residential premises from attic.

In this article we will try to figure out how to properly arrange the basement floor according to pile-screw foundation(screw piles).

Monolithic floor slab on screw piles: how to arrange it correctly

One of the options for arranging a floor on a pile-screw base on screw piles is pouring a monolithic slab.

Preparatory work

Before starting concrete work, metal piles should be shortened to design marks, the cavity of the pipes should be filled with concrete mix. Pile trimming is carried out in such a way as to remove the holes through which the supporting elements were screwed. When performing work on shortening metal supports, use a hose level.

The length of the piles is initially provided bigger size, taking into account the necessary trimming.

Formwork and concreting

A concrete mixture of class B25 and above is poured into the cavity of metal piles.

Screwed pile screw supports are interconnected by a welded frame, for which rolled metal (I-beam or channel) is used. A monolithic slab is poured in such a way that the metal grillage with its lower part forms the frame of the future slab. Under the metal strapping, the slabs are arranged with a continuous formwork, making sure that there are no gaps in the wooden shields.

The side formwork is erected to the required height, taking into account the expected thickness of the future floor slab. Floor slab reinforcement ground floor it is made by two layers of a special reinforcing mesh, after which the structure is poured with a concrete mixture. On top of the slab, the concrete mixture is carefully leveled.

Concrete care, waterproofing and insulation

Concrete gains strength in 28 days, so it is not recommended to load the slab during this period. In hot weather, to care for the concrete surface, periodically sprinkle the flooded structure with water, and also cover it with a protective film.

Formwork from a monolithic floor slab can be removed after 14 days, when the structure gains up to 70% strength.

The finished floor slab should be carefully treated with waterproofing agents using the technology of using roll or coating insulating materials. The most reliable insulation against moisture and emerging condensate is penetrating waterproofing.

On top of the waterproofing layer, insulation of the surface of the monolithic floor slab should be provided.

Overlapping on screw piles for a log house

The environmental aspect plays a far from small role when choosing materials for the construction of a residential building or a bathhouse on piles. If the foundation of the house is made of screw piles, the upper part of the building is very often erected from wooden materials.

Wood belongs to the classic, environmentally friendly building materials that have been used for centuries for the construction of baths, houses and outbuildings. How to properly arrange the ceiling in a log house on screw piles? Let's try to understand the technology of flooring in a wooden building on pile-screw supports.

The technology of erecting a ceiling for a log house on screw supports

After screwing the required number of piles (screw) into the ground, provided for by the project, the supports should be cut to the same level, filled with concrete mix and the heads on each screw support should be strengthened. Strengthening of the heads is done by welding.

Then you can start laying the lower crown, for which a wooden beam or rounded log can be used. Cuts for fixing wooden parts are made strictly above the heads of the pile supporting elements.

There is another way when screw piles are connected with a grillage belt made of metal. Along the entire perimeter of the grillage, metal pins are welded, which, during installation, must coincide with the drilled holes in the wooden parts of the lower trim of the building.

In this case, it is very important not to weaken the bearing ring with a large number of drilled holes. Waterproofing between metal and wood parts must be done very carefully. The connecting pins themselves need to be treated against corrosion (thickly covered with bitumen).

After that, they start laying a log from a bar, then a wooden floor is erected, which is at the same time a floor.

With a log length of more than 3 meters, an additional support will be required, otherwise the wooden floors will sag and spring.

Floor "pie" (flooring of the building on screw piles)

Taking into account that the building on screw piles has an unprotected space below, it is freely blown by the wind, it is necessary to properly arrange the floor of the lower floor. To begin with, a supporting frame made of wood is laid, which is combined with a subfloor made of wooden planks. Watch the video on how to properly make a floor on screw piles.

A layer of film insulation will protect the first floor from weathering heat. Then the main heat-insulating layer is laid, which is covered with rolled film materials for insulation from moisture and steam. The completion of the puff "pie" of the floor, combined with the floor, are the finishing boards.

The following materials are used for the floor insulation device:

Sheet foam - sheets of material are laid on the subfloor. It should be noted that with insufficient insulation from moisture and low temperatures, the foam is easily destroyed, breaking up into small segments. In general, sheet foam, as a heater, does an excellent job. Mineral wool insulation is offered for sale in the form of separate mats or in rolls.

Mineral wool can be slag, glass or stone - all types are perfect for insulating the floor of buildings on screw piles. The material should be protected from moisture. Penoplex, expanded polystyrene - materials perfectly protect building structures from freezing and high humidity. Insulation of floors of buildings on screw piles with polystyrene foam or foam plastic is the most reliable method of all available today.

Pile-slab foundation (SPF) is a combined type of foundation that can withstand increased loads for a long time. Such a foundation consists of two supporting structures: a pile field and a concrete slab. The main purpose of the combined SPF is multi-storey construction. For example, 90% of the buildings of the Moscow-City complex are built on pile-slab foundations.

AT low-rise construction this design is rarely used due to inexpediency and high cost. Installation of SPF during the construction of a cottage or country house justified in the following cases: In areas with increased seismic activity. On heaving soils, while bearing piles are recommended to be further strengthened before the construction of a monolithic slab. In places where the depth of soil freezing is below 2.5 m. When erecting structures sensitive to vibrations (from foam concrete, glass). Construction of an extension to an existing building on a monolithic or strip foundation. Often a pile-slab foundation is used in the absence of hydrogeological survey data of the site. In many cases, the cost of the SPF device is lower than the cost of conducting research. For safety net, future owners of a private house choose this type of foundation as the most reliable and durable.

Calculations of the combined pile-slab foundation

The SPF calculation consists of two parts:

calculation of pile foundation; calculation of concrete slab parameters.

When calculating the pile foundation, the diameter of the piles, their number, the distance between the piles, and the depth of the pile are determined. This calculation is not difficult - it is easy to carry out on your own. The result of the calculations will be a diagram showing the location of the piles.

The calculation of the slab part is more complex. It takes into account the following factors:

the planned load on the slab base; the depth of soil freezing; the presence of a drainage system; the presence and thickness of the cushion between groundwater and the base; the unevenness of the pile foundation; the conditions for the interaction of the slab with the soil, etc.

If you have certain knowledge to calculate the SPF, you can use professional program GeoPlate, which will allow not only to accurately determine the parameters of a concrete slab, but also calculate the settlement taking into account all physical and geometric data.

Accurate engineering calculations are mandatory during the construction of multi-storey buildings.

When constructing a private low-rise building and taking into account the fact that the load on the SPF is distributed in the following way: 85% - on piles and 15% - on a slab, as well as a small building mass, complex calculations of the slab part can be neglected. The thickness of a monolithic slab depends on the brand of concrete mixture used to fill it, the area of the structure and its mass. heavy building materials(ceramic brick, reinforced concrete) optimum thickness slabs will be 30-40 cm. A structure of the same area, but erected from lightweight materials, needs a base 20-30 cm thick. For light structures and small houses 6x6 m, a 10 cm thick slab is enough. the amount of concrete mix for the SPF device: base area x thickness in meters = amount of concrete (m3).

Settlement calculation

Settlement calculation is also carried out in professional engineering programs such as PLAXIS. When building a house weighing up to 12-15 tons, the foundation settlement will be no more than 1-3%, so it is not necessary to make complex settlement calculations. However, if construction is carried out on heaving soils, then it is better to make a calculation and, taking it into account, continue construction.

If you have engineering experience, special knowledge and all the initial data, you can make the calculation yourself, guided by the standards of SP 24.13330.2011. Of all the calculation methods, it is recommended to use the simplest - the layer-by-layer summation method with the calculation of the settlement of each individual pile. Ideally, it is better to order a settlement calculation to a design organization along with the development of a house project.

SPF construction technology

The general construction technology is described in SP 22.13330. In accordance with the standards, the process of arranging a pile-slab foundation includes the following steps:

Preparatory work

This concept means clearing the site of debris, leveling, marking the location of the piles according to the scheme.

Also at this stage, the issue is being resolved with the purchase or manufacture of a concrete mix for the slab. Considering that it is better to pour the foundation slab at a time, it is better to order concrete at the nearest RBU. Mixing this amount of concrete on your own is almost impossible, but if you have the appropriate equipment, experience and a few helpers, you can make the mixture on the site.

Installation of piles

Piles are mounted in different ways, depending on their type, depth, site features, etc.

In the field of private housing construction, the most popular option is screw piles. They have many benefits: affordable price, wide choice of standard sizes, simplicity of installation. The slab foundation on screw piles will last at least 20 years, and under favorable conditions up to 50 years.

Installation of screw piles can be carried out manually or mechanically. After the piles are immersed in the ground to the desired depth, they are leveled by trimming. Further, a slab part of the base is installed on the finished pile field.

Slab arrangement on screw piles

The slab part of the SPF is made in the following order:

Piles sticking out of the ground are combined with a metal grillage. For the grillage device, channels and corners of size 20 or 30 are used.

Elements are installed along the perimeter and inside the pile field along the pile installation lines. The pile field is covered with a gravel-sand mixture, which forms a “cushion” for the future slab part of the SPF. A footing is cast - a screed of lean concrete grade B7.5 10 cm thick. The purpose of the footing is to level the surface for laying waterproofing and insulation. Installation of waterproofing.

You can use both modern waterproofing membrane films, bikrost, technonikol, and the classics - roofing material, waterproofing. Installation of thermal insulation. The monolithic base slab will simultaneously be the bottom layer of the floor in the house, so it is better to put insulation right away to make the floor warm. Foam boards 10-15 cm thick are used as thermal insulation. Along the perimeter of the future monolithic floor formwork is installed.

The height of the formwork should be 10 cm higher than the height (thickness) of the slab. Inside, reinforcement is performed with a profile with a cell size of 30 cm. It is advisable to lay the lower layer of the reinforcing mesh on a polymer vapor barrier lining that will cover the insulation. The upper part of the reinforcing cage is connected to the outlets of the grillage.

To strengthen the structure, U-shaped metal elements from reinforcement are mounted along the ends. Pouring with concrete grade B15 or B20.

To evenly pour the entire concrete mass in a single direction, it is necessary to use a concrete pump. Truck mixers delivering concrete are always equipped with such equipment. The rule is used to level the concrete layer. Compaction is carried out using vibration equipment.

The pouring of a monolithic foundation on piles begins from the places where the external pile supports are located. Compaction should also be carried out first around the piles, and then over the entire area of the slab.

The foundation on screw piles with a monolithic slab finally hardens in 7-10 days.

During the hardening process, it is recommended to observe the temperature regime. In dry weather and temperatures above +22, it is necessary to water the slab every 2-3 hours to avoid cracks. In the presence of precipitation, it is necessary to cover the SPF with a film or build a temporary canopy.

Pile-grillage foundation with a monolithic slab

The purpose of the grillage is the correct distribution of the load and the connection of two types of foundation: pile and slab by combining pile heads. For this type of SPF, it is better to use not a metal, but a reinforced concrete grillage. For the installation of a reinforced concrete grillage along the pile heads, formwork is performed, reinforcement is carried out, and then the grillage is poured with B10 grade concrete.

After the monolithic grillage gains strength (after 7-10 days), they proceed to the installation of a monolithic slab. Phased construction in this case is similar to the processes that are performed when constructing a foundation on screw piles with a metal grillage: footing, waterproofing, insulation, formwork, reinforcement, pouring a concrete mass, tamping.

Pile-grillage foundation with a slab can have different heights:

Elevated - located above ground level.

This is the most convenient option, which allows you not to do complex settlement calculations. Zero - the height corresponds to the ground level. Its device is more complicated and is possible only on stable soils. Recessed - located below ground level. Due to its complexity, it is not recommended to use it in private housing construction.

If you still decide to make a zero or in-depth foundation, then use the formwork not removable, but monolithic. However, keep in mind that this will lead to an increase in the cost of the already expensive SPF with a grillage.

Pile-slab foundation on bored piles

In addition to screw piles, bored supports can be used for the SPF device.

This is a type of pile, during installation of which holes of the required depth are drilled in the ground, and then filled with concrete and reinforcement. The most popular option is I-shaped barrettes. The lower part of the pile rests on the bearing dense soils, and the upper part protrudes above the surface.

The use of bored piles is advisable where screw piles cannot be used.

For example, in soils with high alkalinity, because in this case, metal screw supports will quickly become unusable due to corrosion and lose their bearing capacity.

Advantages of SPF with bored piles in comparison with screw piles:

able to withstand 20% more load with the same diameter of the supports; resistance to corrosion, aggressive environments; drilling does not affect neighboring buildings, so these piles are often used when building an extension to an existing structure; long service life - at least 100 years.

If it is necessary to build an extension, bored piles will successfully coexist with screw piles in the same building, fully fulfilling their functions.

Installation of bored piles

The algorithm for constructing a monolithic slab on a pile foundation with bored supports is as follows:

In accordance with the scheme, drilling of wells of the required depth is carried out. The drilling method is selected based on financial opportunities owner, site location, type of soil, etc. In the construction of cottages, an inexpensive and effective method of manual auger drilling is most often used. Then, a casing pipe is stopped in the well, which will act as a formwork for reinforced concrete bored supports.

The pipe can be metal, asbestos-cement, reinforced concrete. Soil is poured into the free space between the pipe and the walls of the well and compacted. Using the building level, the casing pipes are aligned in height. As in the case of a screw foundation, it is recommended to make an SPF of an elevated type.

Pipes should rise 30-50 cm above ground level. Excess pipes are cut off. The well is filled cement-sand mortar on cement not lower than grade M300. The mixture is compacted using submersible vibration equipment.

In the absence of an electric vibrator, a hand-held vibrating tool can be used. Before the cement-sand mixture hardens, a metal frame is lowered into the well under pressure. It is quite problematic to do this manually, therefore, in the absence of special equipment, it is possible to install a reinforcing mesh inside the casing pipe, and then fill it with cement mortar. In this case, tamping should be given special attention!

The supports are interconnected by a reinforced concrete grillage. After the grillage has hardened, a monolithic slab is mounted using standard technology.

Conclusion

Combined types of foundation: pile-slab, pile-grillage and on bored piles not common in private construction.

There are no statistics on their use. Approximate calculations show that SPF costs 50-80% more than a conventional pile or slab foundation. When calculating the estimate, it is necessary to take into account the costs of renting equipment, delivery and purchase of concrete mix.

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Slab on screw piles is perhaps one of the most reliable foundations. Reinforced concrete slab on screw piles has a number of features. Subject to compliance with all requirements in the process of carrying out work on the installation of this type of foundation, the customer will receive a full-fledged grillage that can withstand heavy loads of buildings made using stone materials.
Screw piles under the slab must be buried to the limit required depth at least two meters. Each site has its own depth of installation of screw piles. Piles are twisted into the ground and leveled (cut off) into one horizontal level. The height of the upper parts of the piles is leveled at 25 - 30 cm from the soil surface, then sand is poured 20 cm and compacted with a vibrating plate. The vibrating plate can be replaced by pouring water, this will compact the sand cushion before further installation of the foundation. Next, a reinforcing mesh of 16-18 mm reinforcement is knitted on the prepared base. Reinforcing wire is inserted into the shafts of the screw piles and tied with the reinforcing mesh of the slab. Next, the formwork is installed and the concrete solution is poured. The thickness of the slab must be at least 25 cm and have two "layers"! reinforcing mesh. The device of such a reinforced concrete slab has a number of advantages. Such a slab for a rather heavy structure can be installed on rather difficult soils without huge material costs for materials and preparatory work. The time spent on building such a foundation is much less than a slab with the preparation of a massive “cushion” using sand and gravel. Of course, a foundation made using special equipment mechanically will be much better than a manual device.

Screw pile reinforcement for concrete slab

Another method involves the creation of a power frame from a channel or two T-beams and filling its base with concrete mortar.

The device of the slab on a screw foundation

These methods have an important difference; in the first, it is necessary to reinforce the pile field with reinforcement in two layers, setting up the formwork and filling it with concrete, in the second, the steel frame itself is filled with concrete, where the bottom is arranged as a non-removable formwork or directly on a sandy base.

When installing a bath on screw piles, a concrete floor arranged on a steel frame can be the first priority solution, where it is quite easy to arrange a drain and waterproofing.

Concrete slab on screw piles

Foundation slab on screw piles- another way to device w. b. foundations on screw piles. How might it look?

On pre-installed screw piles and prepared - filled with concrete mortar and "aligned" in one required height mark, a finished b.zh. is installed. factory-made concrete slab.

monolithic reinforced concrete slab on screw piles

Of course, such a solution requires a specialist. equipment - a crane or a hydraulic manipulator capable of transferring and easily installing the product on a finished base of screw piles. This method allows you to quickly produce a device and. b. slabs on screw piles and avoid time-consuming work on reinforcement and formwork. But it must be taken into account that it is better to install piles for this method mechanized way With exact calculation loads. It may also be necessary (in individual cases) tie the screw piles with a steel angle and, if necessary, with a channel. On such a foundation, you can safely carry out work on the construction of fairly heavy "stone structures". It's definitely fast way on the arrangement of production areas in a short short time.

There are houses for which only screw piles are enough as a foundation. For example, a bar or a log can be perfectly placed on separate piles: from one pile to another.

But there are houses that, according to technology, require a grillage as a base, for example, foam concrete or aerated concrete.

And yet, there are cases when screw piles allow you to save money and get away from expensive work on drainage, peat removal, waterproofing and others. This may be due to site moisture, soil heterogeneity, uneven terrain, deep peat, or simply the customer's request that the slab does not lie on the ground.

SVF Group solved this problem by combining two technologies - a monolithic slab and Aster ® piles of the SV series.

Advantages:

It is convenient to use when the installation of concrete piles is difficult or impossible, high level groundwater, high flow rate, peat.
Installation speed is reduced by 50%.
The cost of Aster ® piles of the SV series is less than concrete analogues.
No need for peat sampling.
High bearing capacity of piles Aster ® .
Effective use concrete, money is not buried.
The complete absence of seasonal shifts.
Guaranteed.

Slab on piles can be of two types:

Slab "hanging" on screw piles

Slab on piles, where the screw piles are the support for the slab.

Additional advantages of a combination of foundation types:

Practical. The plate will never be wet.
Economical and fast. The minimum amount of preparatory work.

Eco-friendly and tidy. The landscape is not damaged, there is practically no debris.

Usage pile-slab foundation is quite common, since this type of structure base is excellent for erecting on planting soil areas. In its own way, the invention is unique, because it has increased stability and strength.

A feature of the slab-pile foundation is that it consists of a grillage, a slab and concrete piles. If construction is supposed to be carried out on a site with moving soil, which is characterized by seasonal swelling, the developer cannot find a better option than a pile foundation with a monolithic slab. A base of this type can be used, among other things, for multi-storey construction, since it has a large bearing capacity. In addition, a slab foundation on piles can significantly save on the arrangement of a basement or basement. With the help of a pile-slab foundation, the degree of shrinkage of the structure can be reduced.

What to pay attention to?

Pile-slab foundations are combined structures that include two types of foundation at once. As a rule, powerful concrete supports are connected by a monolith, which simultaneously performs the function of a grillage. Thanks to this combination, the pile foundation becomes especially strong and reliable, which attracts many developers.

Despite the fact that the bearing capacity of the pile-slab foundation is quite high, before starting work on the construction of the base of the structure, it is necessary to carry out calculations in order to determine the total load on the soil when using two types of foundation at the same time. When making calculations, the following factors must be taken into account:

An accurate calculation of the forces that act on each support in the foundation.
The total stiffness of all piles.
The nature and degree of interaction of piles buried in the soil with a monolithic slab.
Possible manifestations of irregularities in the placement of supports, their uneven location.
The impact of supports on the soil, as well as their interaction with each other.
The impact of the monolith on the ground.

When building a pile-monolithic foundation, it should be taken into account that the load on the foundation is distributed unevenly. The supports account for about 85% of the total gravity of the structure, and the slab itself - only 15%. It is quite difficult to make all the calculations for the construction and strengthening of the foundation on your own. For this reason, it is advisable to contact specialists who will carry out all the calculations as accurately and correctly as possible.

Operation features

A feature of the combined foundation is that the pile foundation is first erected, and then a monolith is installed on top. The plate better fastens the supports to each other, and also gives additional rigidity, strength and stability to the entire base as a whole. Thanks to this design, there is no need to equip the grillage, which is usually provided for during the construction of the foundation.

It is best to install a combined version of the base in the following situations:

When the construction is located on a territory located in zones of increased seismic hazard.
During construction in particularly problematic areas. For example, these may be areas with heaving soils, underground watery layers and lakes, as well as a large depth of soil freezing.

To get rid of the above problems, you just need to ensure the construction of the foundation on piles. Of course, this technology is not suitable in all cases, however, in many situations it will be the only possible option.

In addition, in some cases, the combined base is used to strengthen the supporting belt of the structure. This is necessary for a number of reasons:

The use of a slab foundation associated with a pile foundation is mandatory when building extensions to the main buildings that were erected in problem areas.
The absence of a study of geology at the construction site requires the construction of a foundation of higher strength.
Combined bases are used during the construction of buildings sensitive to vibrations.

Foundation technology

To begin with, it should be noted that houses on a combined pile foundation must be built by professionals. It is simply impossible to independently equip such a technologically complex foundation. All work on the construction of the foundation is carried out in strict accordance with normative documents on construction, as well as in a clear sequence.

The whole process of building a combined base can be divided into several stages:

Expert advice:

Thus, the combined types of foundation, including both piles and a monolith, are the most durable and durable. Such bases are mainly used on more complex soil options, where there is a danger that a conventional foundation simply cannot cope. It is not so easy to make a combined foundation, but its strength allows you to build a truly reliable building. For the most part, combined bases are used in multi-storey construction, since the strength of the foundation is especially important here. The slightest changes in the base can lead to tilts and deformation of the entire structure.

When choosing the type of foundation for a future country house, it is necessary to carefully study the condition of the soil on the site. After all, the durability of the building directly depends on the strength of the foundation. It should also be taken into account that in the near future family circumstances may require the expansion of the living space, and it will be necessary to build on the building with one or two floors. This means that it is necessary to design the foundation with a very large margin of safety. But what if the hydrogeology of the site leaves much to be desired (fragile soil, an abundance of surface groundwater, seasonal flooding, etc.)?

A good solution in this situation would be the installation of a monolithic slab on bored piles. Piles pass through all fragile layers and sink into dense ground, transferring the entire load from the house to solid soil, and a heavy slab will successfully resist the displacement of unsteady soil layers, in this case, bored piles work as racks. If solid ground lies deep, or it does not exist at all, bored piles will work like hanging piles due to lateral friction. In addition to reliability, such a foundation is characterized by low cost, which is important for private construction.

The construction of the foundation begins as standard - with the calculation of the required number of piles, the determination of the required depth of their immersion (recommended at least one and a half to two meters, depending on the depth of freezing), drawing up a diagram of their location and marking on the ground. As a rule, piles are installed in the corners of the house and in the middle of each side of it; it is possible to roughly determine the number of bored piles by collecting permanent and temporary loads from the building and the monolithic slab. There are tables bearing capacity bored piles, depending on the type and density of the soil, as well as the diameter of the base of the piles. Further, inside the perimeter of the future foundation, the vegetation layer is removed, the surface is carefully leveled; if possible, it is better to involve an excavator for this manipulation.

After completion of the preparatory stage, pits for piles are drilled in the ground using a hand drill. Then crushed stone is poured onto the leveled surface, after which it is rammed with manual or electric rammers so that the thickness of the backfill is fifteen to twenty centimeters.

For crushed stone compaction, you can use a vibrating plate that runs on diesel fuel or gasoline. Further along the perimeter, a wooden or metal formwork is assembled. At this stage, it is necessary to provide the necessary communications - to design and place the input of the water supply system and the output of the sewer system.

Now you need to prepare the reinforcement for the supporting piles. It is knitted from longitudinal rods of a periodic profile with a minimum diameter of twelve millimeters, which, approximately every thirty centimeters in length, are fastened in the transverse plane with round metal wire clamps. The number of longitudinal rods must be at least six, the rods must be evenly spaced around the circumference. As a result, a cylindrical structure should be obtained, the diameter of which should be 100-140 millimeters less than the diameter of the wells for piles. For waterproofing a bored pile, even in relatively dry soils, it is recommended to make a pipe from roofing material (with an overlap of up to 0.5 meters), tied with wire and lower it into a drilled hole. The number of layers and the type of vertical waterproofing depends on hydrogeological conditions. In the upper part of the pile it is better to always make 2-3 layers of waterproofing. The connected reinforcement (structure) is lowered into the wells and poured with concrete of a grade of at least 200 (B15).

It should be noted the obvious advantages of using vertical waterproofing in the form of a roofing material pipe:

The pipe inserted into the well perfectly performs the role of formwork when concreting the pile.
The setting of concrete and strength development are improved, since the cement milk will not go into the ground and the strength of the concrete will not decrease.
With dry soils during concreting, the water, which is so necessary for concrete hardening, will not go into the ground and, therefore, the strength of concrete will not decrease.
When the soil freezes, the forces of frost heaving will have less effect on the rough body of the piles, in the presence of roofing material!

It's time to pour the so-called footing - a thin rough layer of concrete mix under the main foundation. It performs several functions: it provides additional waterproofing of the main foundation slab, carries out preliminary leveling of the surface and creates a plane for convenient marking and installation of the reinforcing cage. For the footing, concrete of a grade of at least 200 (B15) is used, it is better to produce it with a rented mixer. The thickness of the concrete layer is usually at least ten centimeters.

Reinforced frame of a monolithic foundation slab

Concrete needs to stand for three to four days, after which markings for reinforcement are made on its surface. The armoframe is made of reinforcement rods in the form of a set of square cells with a side of twenty to forty centimeters, interconnected by a metal wire. The diameter of the rods for the frame is selected in the range from twelve to fourteen millimeters. The armored frame, which is the lower and upper grating on struts, is installed on the draft layer of the footing. The lower grating (grid) of the slab is laid on concrete preparation on special fixators of the protective layer “chairs” or “cubes” to ensure minimum thickness protective layer of concrete 35 mm. When there is no concrete preparation under the monolithic foundation or slab, the thickness of the concrete cover for the bottom mesh should be at least 70 mm. Then, using the same mixer, a slab is poured - with a layer of concrete grade not lower than B22.5 with a thickness of thirty to forty centimeters. This is how the main monolithic foundation slab is formed.

The main layer of concrete is allowed to settle for several days under the protection of a plastic film, after which the entire surface of the foundation is cleaned of debris, dust and dirt, treated with two waterproofing materials: first, a layer of special mastic (primer) is applied, and after a day or two (after the first layer has dried ) is a cold bituminous primer. Foundation construction completed. Now it again needs to be protected from the effects of precipitation with any waterproofing film and left to harden for three to four weeks, during which it absolutely cannot be subjected to any load.

The combination of a concrete monolithic slab and bored piles, in addition to solving certain construction problems, allows you to save a lot on construction without sacrificing quality. For example, a similar foundation with an area of sixty square meters at average market prices, it will cost about one hundred and fifty thousand rubles, including the rental of the necessary equipment (excavator and mixer for pouring concrete).

If you got a suburban area with problematic soil, you should not despair. A monolithic foundation on bored piles will allow you to build a reliable and spacious house that will stand for many years.

Attention! The thickness of a monolithic foundation slab and its reinforcement, as well as the number, diameter, percentage of reinforcement and the length of bored piles depend on the construction area, the load from the building (its number of storeys and design features), type of base soils and hydrogeological conditions at the construction site! In addition, it may be necessary to perform waterproofing for concrete preparation and horizontal or vertical insulation of the monolithic foundation of the slab!

Foundation, monolithic slab on bored piles

Foundation on bored piles: design requirements, preparation of the site and foundation for pre-concrete, pits, waterproofing, creation of reinforcement cages for the slab and piles, pouring the foundation slab