Construction of a bored foundation using a monolithic slab

Just a couple of decades ago, the priority of using solid foundations (aka slab foundations) belonged to multi-story construction - buildings were erected on such foundations on unevenly compressed low-strength soils. However, with the advent of effective materials intended for the construction of low-rise housing, a slab foundation with a grillage has found a second life. What are its advantages and what are the features of the device will be discussed in this article.

How to avoid mistakes when choosing a foundation?

Perhaps today, the most popular type of foundation in Russian country house construction is strip.
It is considered strong and reliable enough to withstand the weight of any private home, it is warm enough, and also “tolerates” difficult climatic conditions well. It seemed like, what is there to think about? We take a strip foundation (or slab foundation, or other analogues) and begin building a house on our site. But it was not there.

The fact is that on certain types of soil, concrete foundations will turn out to be extremely unreliable and the house, at best, will become covered with cracks, or even completely warp.

To avoid such problems, when choosing the foundation for a future building, you should definitely conduct a geological survey of the land, check the quality and strength of soil heaving, the depth of groundwater, the depth of freezing, the density of soil layers and much more.

Depending on the condition of the soil, the weight of the future structure and its area, in accordance with your financial capabilities, you can already decide to build a certain type of foundation.

If you find that the soil on the site is loamy or sandy, then keep in mind that it is prone to movement, and in winter it expands. In this case, conventional strip or monolithic foundations are not the best solution.

General information

A slab foundation can be made in two ways: using ready-made reinforced concrete slabs or pouring a monolithic base.

In the first case, suitable for use are road slabs laid closely one to one on a prepared base with a cushion and waterproofing.

Sectional diagram of laying a slab foundation

This project provides for quick installation, but requires additional costs for the use of special equipment for transportation and loading and unloading operations.

The features of a slab foundation lead to the need to carry out rather complex calculations to take into account the effects of loads in different sections of the slab. For qualified design of this type of foundation, you should use the “Guidelines for the design of slab foundations for frame buildings and tower-type structures.”

This manual provides recommendations on the selection of foundation parameters and design schemes. It allows you to determine the preliminary dimensions of a slab foundation based on the criterion of minimum concrete consumption. The features of the design and construction of slab foundations are described. Requirements for measuring rolls, settlements and shears are given.

Like a strip base, a slab base is laid on a pre-compacted bed of a mixture of sand and gravel.

Then waterproofing and reinforcement cage are installed on it. When reinforcing, you need to use two reinforcing meshes - upper and lower, which are rigidly fastened with wire to one another. Reinforcement for slab foundations is used from 12 mm to 16 mm in diameter. It must have a variable cross-section, that is, be ribbed. If a strip foundation is being erected, then ribbed reinforcement must be used only for longitudinal reinforcement.

Such a foundation of the house experiences a load in the longitudinal direction, because its width is less than its height. And the slab foundation is subject to loads in all directions.

The distance between the reinforcement bars is maintained at 20 - 40 cm. If the reinforcement is laid in increments of 30 cm, then approximately 14 m of reinforcement will be used per square meter of the slab. When pouring, a monolithic slab foundation requires more reinforcement and concrete consumption than other similar types of foundation. Accordingly, the cost of its construction is higher.

Scheme of reinforcement and concrete pouring of a slab foundation

Slab foundations are divided into ribbed, box-shaped and solid.

If the structure is planned to be built without a base, then a continuous floating foundation is erected, and the slab will be the floor in this case.

A slab foundation with stiffening ribs is used in the construction of residential buildings, and the height of the rib will be equal to the height of the base and will be located on the underside of the slab, that is, directed downward. The top of the slab serves as the floor in an unfinished room. Such ribs are made from a concrete monolith or reinforced concrete blocks are used.

The advantages of such a plate:

• the slab becomes more resistant to deformation;
• Stiffening ribs prevent the slab from moving in the horizontal direction.

A box foundation that can withstand heavy loads is erected during the construction of a multi-story building.

Drawing of several options for a box foundation

It looks like a ribbed base and the height of its ribs is equal to the height of the wall underground; the ribs are connected to each other by a floor slab, thereby forming a concrete box.

A monolithic slab foundation can be deeply buried or shallow. The deep foundation is poured into a previously dug pit. This provides increased load-bearing capacity of the structure. But the presence of such characteristics for private construction does not make sense, so this type of foundation is used in it quite rarely.

A shallow foundation involves removing part of the soil and having a cushion of a mixture of sand and gravel, the depth of which is up to half a meter. As a result, the upper surface of the slab should be slightly higher than the ground level - about 10 cm.

Construction work on pouring the foundation is necessarily included in the house design. To calculate the need for a supporting plane for a house, you need to correlate the load on the foundation and the bearing capacity of the soil. A floating foundation is best suited for construction on weak or unstable soil or in areas with high groundwater levels. A slab-pile foundation also serves for the same purposes.

Types of pile supports

The construction of a pile foundation with monolithic inclusions can be carried out in various options:

• A base with a hanging grillage, the design of which includes a small hole between the grillage and the soil, up to one hundred millimeters, so that externally the base of the house seems to hang over the soil. This technology is used to protect the monolithic surface from the bad effects of the soil. This type of foundation is used by specialists for the construction of structures from various materials.
• With the deepening of the foundation piles into a special monolithic foundation grillage. With this technology, there is no distance between the base and the soil, but there is a base, which is ensured precisely by the grillage. When using conventional pile supports, it will not be possible to build a base. The grillage can be made from a variety of options, including concrete, reinforced concrete, wood and steel. Reinforced concrete is considered the most suitable, durable, reliable and safe option (according to experts).

In order to equip a pile-grillage foundation using a monolithic slab, it is necessary to first perform a number of preparatory works:

1. Select the piles of the required size, and also cut down the heads of the supports to the desired size.
2. The upper part of the supports is cleaned, rinsed well, and then air dried.
3. Formwork construction is in progress.
4. To install removable formwork, it is protected from the mortar, usually using polyethylene.
5. The monolithic grillage is being poured. Concrete is poured in successive layers over the surface.

Marking and digging a pit.

The geometric dimensions of the pit for a monolithic foundation slab should exceed the dimensions of the future house by 0.5 m on each side.

This will simplify the installation of the formwork. The marking is done with a beacon cord stretched between the reference points. The position of the points is determined by the plotter, tacheometer or other geodetic instrument.

Digging a pit can be done either manually or with a small excavator with a leveling bucket without teeth. In this case, the fertile layer of soil is first removed and transferred for temporary storage.

The optimal depth is approximately 0.5 m.

An additional small trench 25-30 cm deep is made under the grillage in the pit. The surface of the trench and the main pit is leveled and compacted. It is recommended to immediately strengthen the outer wall of the trench for the grillage with formwork.

Purpose

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

In addition, the following foundations are recommended:

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

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

House on chicken legs?

A pile foundation fits very difficult into the Russian people’s system of ideas about the foundation of a house - a frame structure on piles is popularly called a “cardboard house on chicken legs.” After all, we are building to last (so that our grandchildren and great-grandchildren will have it), with a huge margin of safety (just in case). And everyone understands that concrete is stronger and more durable than even the best steel. So the choice is obvious? But no.

Economic conditions change the national mentality, sometimes forcing us to solve housing problems here and now, for ourselves, and not for future generations. For example, the cost of St. Petersburg apartments makes building a house in the suburbs a very profitable enterprise, and technologies for cheaper construction of light wooden houses allow the use of pile foundations, which significantly reduces the construction budget. And the reasoning about the durability of the building now looks like this: “It’s enough for my lifetime.”

So, what are the possibilities of a pile foundation for wooden houses? Firstly, it can be erected on any soil (except rocky); secondly, construction does not depend on the season; thirdly, it happens very quickly (in one or two days); fourthly, inexpensive. Additional savings can come from replacing the concrete grillage with metal or wood framing. And note, when the construction work and facade finishing are completed, no one will ever guess on what foundation your wooden house stands.

Types of pile foundations with grillage

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.

Scheme of a bored foundation

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.

Soil samples.

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.

In the first option, the load-bearing capacity of the pile will be 15.4 tons, in the second 10.7 tons, in the third 7 tons. With the same prefabricated load from the dwelling, the maximum pitch of the pile field for the first case will decrease in the last two options by 0.8 m, 1. 6 m, respectively. That is, three-meter piles will be needed 2.2 times less than two-meter ones.

The prefabricated load on the pile field is calculated (weight of the roof, floors, wind, snow load, furniture, weight of floors, walls, foundation, internal stairs, equipment). The resulting figure is divided by the load-bearing capacity of the pile, taking into account a safety margin of 15 - 30 percent for possible redevelopments and extensions.

The width of the grillage depends on the parameters:

• pile diameter - for rubble concrete and reinforced concrete structures, the minimum size is 50 and 30 cm, respectively;
• wall thickness - it is allowed to widen the masonry with the lower rows by 10 cm in each direction;
• protective layer - 3 cm from the reinforcement to the outer edge of the grillage.

Thus, the minimum cross-section of the grillage is 40 x 35 cm (width, height, respectively). The depth of the grillage is selected depending on the characteristics of the soil and the construction budget:

• the hanging grillage will have to be protected with a fence at the end of construction;
• under a low grillage after stripping, it is necessary to remove a layer of soil/sand 10 - 15 cm or place one or two layers of foam plastic before pouring into the formwork;
• a high grillage allows you to place communications underground;
• ground grillage allows you to make floors on the ground, which are the most economical option for flooring.

The distance between the monolithic grillage and the blind area of ​​45–50 cm is considered the most convenient for the entrance porch. An odd number of steps (in this case 5 pieces) is more convenient than an even number. In addition, the resulting height of the intake is sufficient for the manufacture of ventilation ducts in the underground. They will not be covered with snow in winter at a height of 35 cm from the blind area.

Marking, excavation, input of communications

Marking the pile foundation

According to existing standards SP 70.13330 regarding geodetic work in construction, the maximum error when marking the foundation is 10 mm. For a pile foundation, the technology for transferring axes from the project to the construction site has the form:

• installation of cast-offs - structures of two pegs with crossbars are placed at the corners, cords are pulled along them along the axes of the future walls, and internal walls are marked in a similar way;
• marks for piles - the centers of corner piles are marked with lime mortar, chalk or paint on the ground, distances equal to the design pitch of bored structures are set off from them with a tape measure, in these places a plumb line is lowered from a stretched cord, similar marks are created.

According to SP standards, the minimum diameter of piles is limited to 30 cm, 40 cm, 50 cm for reinforced concrete, concrete, and rubble concrete structures, respectively. Hand drills with 50 cm equipment are produced by a limited number of manufacturers. Therefore, in most cases, when choosing rubble concrete piles, the developer has to dig pits to the full depth, use support piles, and fill them with non-metallic material after stripping.

If reinforced concrete piles are used, the width of which is 40 cm, there are no problems with the drilling tool. This allows you to avoid a large amount of excavation work without reducing the load-bearing capacity. The depth of the wells depends on the results of geological surveys; it rarely exceeds 3–5 m. To reduce labor costs, a motorized drill can be used, the rental of which is much cheaper than special equipment.

Drilling wells for piles using special equipment.

At the same stage, the supply of engineering systems is carried out. When using a low grillage in combination with insulation of the blind area, a depth of 0.7 - 1 m for water supply and 0.5 - 0.7 m for sewerage under the base of the building is allowed. Communications under a monolithic hanging grillage must be insulated. Thermal insulation technology looks like:

• the pipes are wrapped in mineral wool, with a heating cable in the air;
• placed in polystyrene shells in the ground.

The depth increases to 1.2 - 1.5 m for water supply, 0.7 - 1 m for sewerage.

Formwork and reinforcement

When choosing formwork for drilled piles, the following factors must be taken into account:

• when poured into the ground, the load-bearing capacity of the piles due to friction of the side surfaces fully corresponds to the calculated one;
• if roofing felt rolled into a cylinder is used, the characteristics practically do not change;
• when using an asbestos-cement pipe as permanent formwork, the load-bearing capacity along the side edges is reduced by 10–15%, but the pulling forces during soil swelling are reduced by 30%;
• if a polyethylene pipe is used as permanent formwork, heaving forces have virtually no effect on the piles, however, the load-bearing capacity along the side surfaces is lost by 50 - 70%, all loads are transferred to the sole.

Frame for piles.

Thus, if the height of the drilled pile does not exceed 2 m, the base does not reach the layer with bearing capacity, it is better to abandon polyethylene pipes or reduce the pitch of the pile field by 1.5 - 2 times.

When choosing the height of the formwork, it is necessary to take into account the type of grillage, the depth of the heads into it by 5 - 6 cm. It is at this mark that the lower reinforced belt will be mounted, taking into account 5 cm of the protective layer. The technology for reinforcing reinforced concrete piles is carried out as follows:

• cut - 4 longitudinal rods (this is the minimum value for one pile);
• cutting and bending of clamps;
• ligament – ​​connection of vertical rods with clamps;
• installation - the structure is lowered into the formwork or well, maintaining a 5 cm protective layer.

We recommend: How to properly reinforce bored piles.

Pouring of piles.

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.

We recommend: Proper 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).

Pouring the grillage.

Waterproofing is carried out 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).

How to make a load-bearing monolithic grillage correctly

Monolithic grillage for a pile foundation Considering that a monolithic grillage has a large mass, it has a special feature during installation.
After all, the huge mass of reinforced concrete from the grillage itself and, in fact, from the load-bearing walls and floors of the building will put pressure on the supports. Therefore, in order to ensure maximum structural strength and the ability to withstand seasonal soil movements, reinforcement is indispensable. How to do it correctly?

1. Reinforcement of supports. If the supports are made on a construction site, then it is necessary to install rigid vertical reinforcement bars inside the concrete formwork, interconnected by several reinforcement belts. They need to be done every 50 cm, connected with bolted connections. The vertical edge of the reinforcement should protrude beyond the pile to a height of at least 15-30 cm.
2. Grillage reinforcement. Considering that the monolithic grillage has a huge mass, the entire horizontal belt is reinforced. For this purpose, a uniform arrangement of belts is provided with an interval of 10 cm in height and in increments of up to 50 cm vertically. Then all the belts are connected to each other, as well as directly to the reinforcement of the supports themselves.

Strip foundation on a recessed slab

In projects with an underground floor, the height of the strip part of the slab foundation reaches 2 - 2.5 meters. This complicates concreting in one go due to large volumes of mixture. Therefore, step-by-step filling technology is often used. Vertical lintels are prohibited from being mounted in corners, and reinforcement must not be cut to install panels. Therefore, panels with cuts are used, into which rods are passed, and the remaining cracks are filled with polyurethane foam.

When concreting in stages, the next section can be poured after the previous section has gained 50% of its strength. The joint area is cleaned with a metal brush, steam, or a grinder. All film from the surface of hardened concrete must be completely removed.

Due to large volumes of concreting, formwork requires a lot of lumber and plywood. When treating the inner surface of the boards with polyethylene film after stripping, these materials can be used in the future (partitions, subfloors, roofing, rafter system).

At this height of the tape, two reinforcement belts are no longer enough; more belts are added every 50-70 cm in the middle part. At the same time, the size of the clamps increases; additional elements may be required to ensure a stable geometry (gaskets on the sides for a protective layer).

Types of grillages

There are several types of grillages, each of which should be studied in more detail.

Prefabricated grillage

Installing pre-prepared elements is much faster and more efficient than creating them yourself. Thus, prefabricated grillages for pile foundations are a simple structure consisting of several piles. It is initially manufactured as one element, after which it is specially reinforced using a welded frame for additional protection from mechanical damage.

The resulting structure is installed using cranes, and this is one of the most significant disadvantages, because, among other things, it requires the cost of renting the crane itself, and installation also takes more time and effort.

The prefabricated grillage consists of reinforced concrete beams, which must then be installed on pre-prepared sand beds, due to which they are leveled horizontally. All elements of the grillage are connected by embedding a special hole in the trapezoidal section.

Thanks to the speed of construction and other advantages, which still outweigh the disadvantages, today prefabricated grillages have become most widespread. In addition, they are famous for their good strength and low susceptibility to corrosion.

Also, a grillage is extremely convenient if it is necessary to construct a temporary structure such as country houses or verandas, the service life of which is often limited to 20 years or a little more. After all, these structures can also be erected directly on a waterproofed cap, and without using monocoiling for attachment, and the structure will still remain extremely reliable and durable. An example of use is the lower crown or lower trim, which is used in houses instead of the same grillage.

One of the homemade examples is usually the simplest construction, made by simply welding several steel beams. But the main disadvantage of such a grillage, in addition to those that are produced in factories, is the complexity of installing the connection of the same steel beams, and the structure itself and the welding points remain extremely unreliable.

However, due to their cheapness, such grillages are often used in buildings created for “time”, because they cost much less, and, again, they can be laid directly on the head of the piles, which will save resources. This is the best solution for creating a non-permanent building.

Prefabricated monolithic grillage

As an intermediate option, a prefabricated monolithic grillage is used. It is made from prefabricated factory elements. Their assembly using keyed connections and locks resembles a kind of “constructor”. Upon completion of assembly, the joints are sealed, forming an unseparable tape.

Prefabricated monolithic products are most often used in the construction of industrial or multi-storey buildings. They are expensive and require heavy equipment and maximum precision when installing piles, which only proves their extreme disadvantage in private housing construction.

Monolithic-cast

Monolithic-cast grillages are called ordinary monolithic grillages. They are reinforced concrete beams cast in the form of a slab or beam. Regardless of design variations, the monolithic-cast grillage is considered the connecting link between the piles.

The piles are either fastened to the grillages or included in them. The monolithic-cast grillage slab is often high; its use is advisable in the construction of low-rise buildings.

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 regulatory documents for construction, as well as in a clear sequence.

The entire process of constructing a combined foundation can be divided into several stages:

1. Preparing the area. The first thing you need to do before starting any construction work is to plan the site. To do this, any debris is removed from the territory allocated for construction, any green spaces are removed, and all holes and piles of earth are leveled. The holes can be filled with soil from the same area, and the piles must be leveled in accordance with the main surface. Then the area for installation of piles is marked. Special markings are installed directly on the ground in the places where the support will stand. The contours where the monolithic slab will pass are also marked.
2. Deepening of piles. At this stage, supports are brought to the site. The type of piles is selected depending on the nature of the building and the characteristics of the soil. Types of piles differ in the quality of the material, as well as in size. Reinforced concrete supports are considered the most durable; the size is usually selected depending on the depth of soil freezing. Then special equipment for driving piles is installed on the territory. As a rule, a piledriver and other equipment are used for this purpose. Each support is first installed directly at the point where it will be buried. Then it is leveled, after which it is driven into the ground using a hammer. There are various ways to bury supports in the ground, however, all of them involve the use of heavy equipment during such construction. After installing all the piles, they are leveled. To do this, using special equipment, the heads of the supports are cut to the zero level.
3. Pouring the monolith. After all the supports are ready, you need to start pouring the monolithic slab. For this purpose, the first step is to install the formwork. The resulting box is preliminarily equipped with waterproofing; most often in this case, roofing material is used. Then a special pillow is prepared. A layer of sand about 20 centimeters thick is poured into the box, the material is well compacted and leveled. Next, the same layer of crushed stone is poured and also leveled. The pad is then covered with a small layer of liquid concrete mortar, which will help secure the bulk materials. The thickness of the concrete should not exceed three centimeters. After this, a frame of reinforcement is constructed in the formwork, which is subsequently filled with concrete mortar. During the concrete pouring process, certain technology must be followed. For example, the solution should be poured into the box from both sides.

Expert advice:

• After the concrete solution is completely laid in the formwork, it must be leveled and compacted. This action is carried out using vibrating rammers. Next, the monolith is left to dry. Complete hardening of the concrete slab is observed 30 days after it is poured. While the concrete is drying, you need to take care of the slab. To do this, you need to cover the monolith with film and lightly moisten it several times a day.
• Caring for the surface of a monolithic slab helps prevent improper and uneven drying of the concrete solution. After the concrete has completely dried and the slab has become as strong as possible, you can begin constructing the remaining structural elements of the building.
• In some cases, USHP is used as a base - this is an insulated Swedish stove. USP is not just a concrete slab, it is the most modern and effective foundation that performs several functions at once. Such a slab includes a communications system, heating the entire area of ​​the house with heated floors, already installed sewerage systems, water supply and even marking electrical cables. USPs have a smooth surface, which allows you to lay the finished floor covering directly on the monolith.
• USP is often used in the construction of structures made of aerated concrete, frame houses, buildings made of logs and beams. The advantage of USP is that it can be erected in almost any area, regardless of the nature of the soil. The technology for constructing such a base involves various options for arranging a monolith, which makes it possible to make a base.

Design features of a pile foundation with a monolithic grillage

There are two options for making a monolithic grillage:

• slab - grillage that connects all piles into a single system;
• tape - a grillage connecting the piles in series.

A slab grillage is installed under the entire area of ​​the building, a strip grillage is installed only under load-bearing walls.

The most common in private construction is a strip monolithic grillage, since particularly heavy buildings are not erected in individual households, and the material consumption of a slab grillage is several times higher than a strip grillage.

In turn, the tape grillage is also divided into several varieties, characterizing its position relative to the ground:

• hanging (high) – placed above the surface of the earth. The distance from its sole to the ground is at least 10-15 centimeters. This type of grillage is advisable to use on heaving soils;
• ground - a grillage, the base of which lies at the level of the ground on a cushion (sand-gravel or sand). This design is acceptable only on non-heaving or slightly heaving soils. Soils subject to heaving during frosts can tear the grillage away from the piles;
• low – recessed grillage. In heaving soils, it is buried to the freezing depth; on more favorable soils, the depth of immersion of the grillage into the soil can be only 200-400 mm.

Of all the types of grillages, the most common in individual construction are hanging ones: they are strong enough to serve as reliable support for light buildings. Their installation does not require excavation work.

Most buildings (dachas, bathhouses, etc.) are built using a foundation on bored piles with a monolithic grillage - the cheapest and least labor-intensive option.

Materials used

The grillage is classified according to the source material. Highlight:

• lungs (wood);
• heavy (metal, concrete).

Diagram of all elements of the foundation slab

Wood species are used to create lightweight structures. The woody type requires mandatory measures to protect against various pests and moisture.

Serious structures require the use of reliable materials such as reinforced concrete or reinforced concrete. This is the most justified grillage option. It is durable and is made directly during the main construction, which helps reduce its cost.

The use of the metal type is extremely rare. The popularity of this option is fading due to its high cost, low practicality and complex installation. Its use requires special processing, which increases the cost several times.

When to use a pile-grillage foundation?

It is advisable to build such a structure in the following cases:

In order to save money. Sometimes this approach helps save up to 30% of the money set aside for the manufacture of the foundation. But you shouldn’t go to extremes: if the calculation shows that the foundation will require more than a dozen piles, think about it: maybe it would be easier to fill in a tape or slab? This foundation option is suitable only for small houses.

If the soil, due to its qualitative characteristics, does not allow the construction of “classic” types of foundations in a short period of time. A pile foundation with a monolithic grillage is designed for soft soils, as well as in areas characterized by a soil freezing depth of 1.2 - 1.5 meters. If there is stable, hard ground under the house being built, it is better to make a tile or strip base.

If the load from the house is low (the house is not made of stone or brick). This type of foundation is perfect for light or medium-sized buildings, as confirmed by numerous reviews on the Internet.

Features of the fundamental basis

Each of the component parts takes on a portioned load, namely: slabs 15%, piles 85%. The difficulty lies in the correctness of the calculations. Incorrect data will lead to increased pressure. If the height of the building is up to three floors, then the construction of a slab without a grillage is allowed. This is an additional part of a horizontal pile-type foundation, which transfers the load of supporting structures to the piles. As an additional function, the grillage is used to evenly distribute the load over the surface.

The feasibility of constructing an SPF:

• in geographical conditions where there is a high level of seismic activity;
• where there are problem soils with exceeding heaving and freezing depth. As a rule, a pile foundation is used. But, if designers are planning the construction of a multi-story building, then they reinforce the base with a slab type;
• The construction of SPF is relevant when the structure is sensitive to vibrations or is made of foam concrete;
• if you plan to build an extension to an already finished structure;
• there is no reliable data on the construction site, type of soil base, characteristics, composition.

There is no need to experiment during construction. Failures or errors lead to the destruction of the structure.

Types of SPF according to grillage location:

• low level;
• high level;
• foundation without grillage.

Feasibility of construction

Choosing this solution is advisable only if:

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

Features of operation

A special feature of the combined foundation is that the first step is to build a pile foundation, and then install a monolith on top. The slab better holds the supports together, and also gives additional rigidity, strength and stability to the entire base as a whole. Thanks to this design, there is no need to arrange a grillage, which is usually provided when constructing the foundation.

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

• When construction is located in areas located in areas 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 large depths of soil freezing.

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

1. The use of a slab foundation coupled with a pile foundation is mandatory when constructing extensions to the main buildings that were erected in problem areas.
2. The lack of geological research at the construction site requires the construction of a foundation of higher strength.
3. Combined foundations are used during the construction of buildings sensitive to vibrations.

Existing types

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

There are:

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

The materials for making piles are:

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

There are three main types of pile foundations:

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

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

Backfill.

Laying geotextiles.

The use of geotextile will increase the bearing capacity of the soil.

Laying a layer of crushed stone.

The point of laying a crushed stone layer is to organize a cushion under the foundation. In order for the load to be more evenly transferred from the foundation slab to the ground, the thickness of this cushion should not be less than 20 cm.

Layer of sand.

A layer of sand 10 cm thick is poured on top of the crushed stone. It is designed to protect the overlying waterproofing from the sharp edges of pieces of crushed stone.

Waterproofing.

Most often, thick polyethylene film or other material with similar physical characteristics is used as a waterproofing layer. It is not recommended to use roofing felt or other material prone to gradual cracking.

Waterproofing sheets are overlapped with significant overlap. The edges of the canvases should extend beyond the top cut of the formwork.

What are piles made of?

Piles include elongated steel rods that are screwed deep into problematic soil.

A pile foundation consists of a pile of piles, which are consolidated by a grillage. Piles are made of reinforced concrete, wood and metal.

The use of wooden piles is based on medium and light loads. The material for making this type of piles is coniferous trees, most often pine.

Driving of wooden piles is carried out using a mechanical hammer, a diesel hammer and a vibratory hammer.

Reinforced concrete piles are created from concrete. Another name for them is driven piles.

On construction sites, the most in demand are solid hollow reinforced concrete piles with a square or round cross-section.

Piles can be divided into subtypes: friction piles, which transfer the main load exclusively through the lateral surface, as well as rack piles, which penetrate deep into the soil through an unstable layer and, reaching harder soil, resting against it, delegate the entire load.

Main advantages

• The foundation on driven reinforced concrete piles with a grillage has an increased degree of strength and safe operation.
• Minor amount of earthwork.
• Minimum consumption of building materials.
• The ability to carry out planned operations at any time of the year, regardless of weather conditions.
• No soil subsidence due to swelling or flooding.
• Reduced heat loss due to reduced contact area with frozen soil.
• Saving up to 20% of financial resources.
• No significant time expenditure during the construction of the foundation.

Classification of pile grillages by degree of depth

In relation to the surface of the earth, the grillage can be:

1. Recessed - the tape is lowered into the soil to a certain depth. As a rule, a strip grillage is combined with concrete and reinforced concrete piles buried in the ground below the frost line. Despite the significant financial and labor costs, such a foundation may be the only suitable option for the construction of heavy structures.
2. Ground - a type of grillage that rests on the surface of the earth.
   Suitable for soils not prone to heaving. Otherwise, there remains a risk of premature wear of the foundation as a result of the destructive forces of frost heaving of the soil.
3. Hanging - a grillage, between the lower surface of which and the zero level of the site there remains an air gap.
   This rise is usually more than 10 cm above ground level. Thanks to the hanging grillage, the vertical forces of frost heaving do not affect the tape. Otherwise, cracks may form in the grillage or a gap may occur between the top and bottom of the base.

How is the minimum height calculated and what affects it?

After placing the points for supports on the plan, proceed to design calculations for the foundation grillage. The dimensions of the grillage should not be less than the dimensions of the structure that rests on it.

When designing structures of the first degree of responsibility, the minimum grillage height is calculated based on the load-bearing capacity of the supporting structure. The following condition is used as a basis:

Where:

• a1 and a2 – dimensionless coefficients;
• bk and dk – dimensions of the pile section;
• c2 and c1 – distance from the faces corresponding to the dimensions and to the nearest piles;
• h1 – working height of the grillage section;
• Rp is the lateral surface of the punching pyramid, taking from the top of the reinforcing mesh to the bottom of the glass.

The calculation rules for the given sample are described in detail in the Recommendations for the calculation of reinforced concrete grillages for pile foundations.

In low-rise construction, the conventional grillage height is taken to be 30-40 cm; in practice, this value may exceed the specified limits.

In fact, the parameter depends on a number of factors:

• geographical conditions of the site;
• climatic conditions in the region;
• design features of the structure being constructed;
• the material from which the foundation is made;
• option for installing the supporting structure;
• the method of impact of the foundation on the ground, etc.

Read about the construction of a pile-grillage foundation and structural calculations in this article.

Required width

The width of the grillage is assumed to be equal to the width of the base or thicker than it. If the house does not have a basement planned, then the width is chosen based on the thickness of the external walls according to the same principle. In this case, the width of the tape cannot be narrower than 40 cm.

Description of monolithic foundation slab

The slab, like all other types of foundations, can be laid below the soil freezing limits, but such a solution is only advisable when the building has a basement floor. In other cases, it is used either as a shallow foundation (with a laying depth of up to 50 cm), or completely superficial.

• The construction of a solid monolith is associated with a considerable need for concrete, and such a solution may not be profitable for some buildings. It is most advisable to use the slab for houses and other buildings with a small plan size, when there is no need to raise the base high.
• It is convenient when the surface of the foundation can serve as a subfloor, although a monolithic foundation slab with a grillage is not quite such an option. The floor pie here has to be assembled quite impressively, but in any case there is a reliable foundation underneath it, which will never sag as it happens in every second case with floors on the ground.
• The difference between the slabs and each other is that they are designed not only in a flat version, but can also have protrusions called stiffeners. These projections can be directed both downwards and upwards, and are located under vertical load-bearing structures (walls, columns).
• The presence of ribs that take the main loads onto themselves allows you to reduce the thickness of the slab itself, reducing concrete consumption. But their reinforcement is carried out more intensively, and the labor intensity of the structure increases due to more complex forms of formwork and frame. In flat slabs, these stages of work are extremely simple, so private developers use this option for independent execution.

Expert opinion Vitaly Kudryashov builder, aspiring author

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The thickness of the slab, of course, depends on the sum of the acting loads, but due to the large area of ​​support, it can be assigned based on the pitch between the load-bearing walls (columns). For flat slabs this is usually 1/6 of the span, and for ribbed slabs it is 1/8 or even 1/10.

What is a foundation grillage

So that any reader can understand what we are talking about, let’s figure out what it is: a “foundation grillage.”

A type of ribbed structure is a slab-grillage foundation, in which the stiffening ribs are directed upward and closed along the perimeter of all walls. It is these ribs that are called a grillage for their similarity to the structure of the same name, although this name is not entirely correct.

Why this is so can be understood by seeking clarification from standard 58033, which presents the official construction terminology. The term “grillage” refers to a structure that wraps around the pile heads and transfers loads to them. A slab is not a pile field - however, in the set of rules 22.13330, which is a guide to designing foundations, the name “slab grillage” is used in relation to upward-directed stiffeners.

The upward-directed stiffening ribs resemble the shape of a strip foundation. The only difference is that the tape transfers loads directly to the ground, and the grillage transfers loads to another foundation structure. Since grillage beams serve as a supporting base for the walls of the house, they are essentially a monolithic base.

Pros and cons of slab foundations

We have explained what a grillage is in foundation construction. Now let's look at the advantages of a slab that is rigidly connected to upward-pointing ribs.

Options for pile-monolithic foundations

• Low pile foundation
  Hanging grillage. This is a base that provides for the presence of an air cushion inside with a height of 70-100 mm. In fact, the floor of the building hangs above the ground and is supported by supports. The advantage of the design is the minimal impact of soil on the lower part of the concrete base.

• Embedding piles into a monolithic base. There is no longer a gap between the soil and the base, but you can make a small basement room. In such cases, the grillage can be erected from concrete, reinforced concrete, steel, wood, and other building materials, and reinforcement must be made.

What materials is the grillage made of?

The strength of the structure also depends on the material of manufacture. For the grillage the following are used:

• reinforced concrete;
• metal;
• tree;
• concrete.

Wood grillage
The first of these materials has become widespread in the production of grillages due to its reliability, rigidity and durability. The main condition is the creation of a sufficient protective layer for the reinforcement. The concrete structure does not require reinforcement, but is used only in the construction of one-story buildings. When using metal in this type of work, anti-corrosion preparation is required. A grillage foundation made of wood is suitable for structures made of similar materials. This base is impregnated with special substances to slow down the process of wood decay.

Grillage type pile foundation - what is it?

A pile-grillage foundation is a system consisting of piles and a connecting monolithic slab. The piles are driven into the ground below the freezing level of the soil, their above-ground part is connected using a grillage (head or frame). The latter is a wooden, metal or reinforced concrete strip, which is located on the ground or just above the surface of the earth.

In practice, different types of grillage are used: prefabricated, monolithic reinforced concrete, precast-monolithic. The first is in its structure a structure of several piles, which are reinforced with a metal frame.

A reinforced concrete grillage is a monolithic concrete slab that is poured directly on the construction site. The prefabricated monolithic type is a cross between the first two types of grillage. Its elements are manufactured at the factory, and at the construction site they are installed on piles and connected using locks and key fastenings.

What types of foundation are there?

The supports that are chosen for the foundation differ in their quality and the method of installation in the ground. This forms the basis for the classification of pile foundations with grillages. There are three types:

1. Screw.
2. Bored.
3. Driven.

For the screw type, metal pipes are used. The internal space of the pipe is filled with solution. This gives greater stability to the piles during the operation of the building. The work of screwing a steel “screw” into the ground is carried out manually or using machinery.

The drilled type involves pouring concrete mortar into a pre-prepared well. The recess is made using a drill and is pre-reinforced. A bored foundation with a grillage is valued for its high strength and stability.

For the construction of large objects, a driven foundation is often used. The supports are immersed in the ground using the impact or pressing method. To drive the pillars, special hydraulic pile-driving machines, steam-air machines or diesel hammers are used. An alternative is to pour reinforced concrete supports into ready-made wells.

The foundations also differ in the level of the grillage. It can be buried, above ground or elevated. In the latter case, the minimum height of the piping above the ground is 30-40 cm. A recessed grillage is in demand in the construction of heavy brick or aerated concrete buildings.

Variety of pile types

For a pile-grillage foundation, different types of supporting elements are used. They differ in structure, material and installation method. The quality of supports is divided into wooden, metal and reinforced concrete supports.

Wooden poles are applicable if wood is used for the structure itself. Country houses, bathhouses, sheds, and gazebos stand stably on such supports. Wooden piles can be mounted individually or in a bundle of 3-4 pillars.

Metal piles can be screwed or, less commonly, driven. The support looks like a metal pole with a pointed or screw end. Piles with a cast tip are considered stronger and more durable. The welded cone is somewhat inferior in technical characteristics. The steel surface of the pipe is coated with an anti-corrosion compound that protects the metal from destruction in wet soil.

Reinforced concrete pile products are made from durable concrete reinforced with metal. In terms of load-bearing capacity, they are superior to metal and, even more so, wood. The service life of the supports is affected by the quality of the concrete used. Reinforced concrete piles can support weights of up to 60 tons.

Pouring concrete.

All work on pouring concrete into the foundation frame must be calculated in such a way as to try to complete it in one day. In this case, special attention should be paid to organizing a continuous supply of concrete solution to the construction site.

Filling is done evenly, starting from the edge of the foundation slab.

Freshly poured concrete solution contains a significant amount of air in its volume. Air bubbles are removed using a deep vibrator. The vibrating device sleeve is immersed in the solution as often as possible to the full height of the slab, waiting for the visible cessation of shrinkage of the liquid concrete.

The grillage is poured immediately after the concrete of the foundation slab has gained strength sufficient to install the inner part of the wooden formwork on it. The outer part is already installed and is integral with the formwork of the foundation slab.

Upon completion of the pouring, the foundation and grillage are covered with a waterproofing film. The concrete curing time is one week. As the concrete under the film dries, the waterproofing should be removed and the surface should be watered.

Arranging a foundation in the form of a monolithic pit with a grillage may be the most reasonable option when building massive houses on soft soils. This option is also attractive due to the ability to decouple the soil and the space under the floor, thereby improving thermal insulation. At the same time, work of this level can be performed either by a third-party team of builders or by the owner of the house under construction on his own.

At its core, a monolithic slab foundation with a grillage is a pile- or column-type structure, the upper part of which is reinforced and combines the pile heads. There are various varieties of it, which are classified according to various criteria depending on the source material, construction method, and are also distinguished by the method location relative to the ground.

Such a foundation can be either strip or solid. According to the first option, the tops are connected by a “line”, and according to the second - by a single surface. Before we move on to considering the features of the material described above, we should decide what a grillage is. This term is used to describe the upper part of a columnar or pile-type foundation base, distributing the load on the main parts of the structure. It is manufactured in two forms - slabs and beams.

They must be installed on poles, after which the load will be distributed over them. They provide support for the entire structure. Among other things, the term “grillage” can also apply to flooring made of beams or logs, which are subsequently laid on the surface. This type of grillage is used when arranging the base for wooden buildings.

The main purpose of the grillage is to accurately and competently distribute the load on the foundation base. Due to the fact that the piles are mounted at some distance from each other, to make the surface uniform, some kind of structure should be used to connect the piles and distribute the load.

This should spread over virtually the entire surface. Among other things, the grillage is able to perfectly overcome the tasks associated with strengthening the foundation. Thus, it becomes much more stable. This eliminates the possibility of piles moving in the event of ground subsidence. Settlement of these elements will also be excluded. We will also answer another question - what is a monolithic slab?

It is one of the varieties of traditional foundations. It can be performed in two types - shallow and shallow. In the second case, the construction of the structure will be carried out at a depth of about 45 centimeters. This type of foundation must be reinforced throughout the entire structure.

This feature distinguishes this type from the strip type. This design difference allows the monolithic type slab to withstand heavy loads caused by uneven soil movement. This is especially relevant and quite important for foundations built on problematic soil. In this regard, the name “floating slab” is also found.

When and which one is better to choose?

A slab on piles is chosen for the construction of multi-storey buildings and industrial facilities, when the rigidity and reliability of the load-bearing structure on unstable soils is important. Such a structure will differ in its resistance to vertical and horizontal loads arising in the ground.

The scope of application of a pile-grillage foundation with a slab is wider. The design features of the system allow the foundation to be used in the following cases:

• the structure has many heavy floors and partitions, which necessitates the need for even distribution of weight on the base;
• the building rests on subsiding and waterlogged soils;
• underground sources on the site are located close to the surface;
• construction is taking place in an area of ​​high seismic activity.

Advantages and disadvantages of a grillage base on a slab

Slab grillage has serious advantages compared to other types of foundations:

• long service life. The durability of the foundation structure exceeds seven decades;
• versatility. A monolithic slab with a grillage can be constructed on various soils, as well as without taking into account the features of the relief;

Concrete grillage is used exclusively for load-bearing walls

• increased strength characteristics and reliability. The use of reinforcement cage increases performance properties;
• expanded scope. The design ensures the stability of various types of buildings;
• simplicity and accessibility of technology. The methods for performing the work are clear and allow you to build your own foundation;
• uniform distribution of forces over the surface of the base. This avoids cracking of the concrete.

Disadvantages include increased costs. Compared to other types of foundations, the costs of construction activities are higher, which is associated with an increased need for concrete mortar and the need to perform excavation work.

Overlapping on screw piles for a log house

The environmental aspect plays a significant role when choosing materials for building a residential building or bathhouse on stilts. If the foundation of the house is made of screw piles, the upper part of the building is very often constructed of wooden materials. Wood is a classic, environmentally friendly building material that has been used for centuries to build bathhouses, residential buildings and outbuildings. How to properly arrange a ceiling in a log house on screw piles? Let's try to understand the technology of installing floors in a wooden building on pile-screw supports.

Technology for constructing a log house floor on screw supports

After screwing the required number of piles (screws) provided for by the project into the ground, the supports should be cut to one level, filled with concrete mixture and the heads of each screw support should be strengthened. The heads are strengthened by welding.

Log house on screw piles

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

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

In this case, it is very important not to weaken the support ring with a large number of drilled holes. Waterproofing between metal and wooden parts must be done very carefully

The connecting pins themselves must be treated against corrosion (thickly coated with bitumen).

After this, they begin to lay logs from timber, then erect a wooden floor, which also serves as the floor.

Floor “pie” (building ceiling on screw piles)

Considering that a building on screw piles has an unprotected space at the bottom and is freely blown by the wind, the ceiling of the lower floor should be properly arranged. To begin with, a load-bearing frame made of wood is laid, which is combined with a subfloor made of wooden boards. Watch the video on how to properly make a ceiling on screw piles.

A layer of film insulation will protect the first floor from heat loss. Then the main heat-insulating layer is laid, which is covered with rolled film materials to insulate it from moisture and steam. The completion of the layered “pie” of the floor, combined with the floor, is the finishing boards.

The following materials are used for floor insulation:

• Sheet foam - sheets of material are laid on the subfloor. It is worth noting that if there is insufficient insulation from moisture and low temperatures, the foam is easily destroyed, breaking up into small segments. In general, sheet foam, as insulation, copes with the task perfectly.
• Mineral wool insulation is offered for sale in the form of individual mats or in rolls. Mineral wool can be slag, glass or stone - all types are perfect for insulating the floors of buildings on screw piles. The material should be protected from moisture.
• Penoplex, expanded polystyrene - materials ideally protect building structures from freezing and high humidity. Insulating the floors of buildings on screw piles with polystyrene foam or penoplex is the most reliable method available today.

Excavation of peat soil

There is another technology for constructing foundations on wet peat bogs - soil excavation. Using this technology, peat is removed from the building site, unless the thickness of the peat layer is insignificant, after which foundation structures are erected on dense soils. Determining the thickness of a peat bog is a very serious operation, in which it is necessary to make several holes in the area in different places, with a depth of 1 to 2 meters. This allows you to better verify the length and thickness of the peat layer.

Peat extraction is carried out using mechanized equipment, followed by site leveling.

There are many ways to construct foundations on weak and wet soils containing peat - it is always worth choosing the most suitable one for each specific case.

Waterproofing and thermal insulation work

Thermal insulation of the floor when installing a high grillage is carried out in the following order. First, to insulate the foundation grillage, fill the empty space under the grillage with brick, stone or rubble masonry, then backfill the internal area of ​​the foundation with careful compaction so that its level is at least 10 cm above the lower edge of the grillage strip. All thermal insulation work is carried out in the warm season .

Watch how the foundation grillage is built - the video demonstrates all the complex aspects of the technology:

Areas of application of SPF

• weak-bearing or loose soils;
• areas with high groundwater levels;
• presence of seasonal flooding;
• wetlands;
• peat bogs;
• high level of frost heaving.

These conditions require the use of reliable supporting structures - piles. They transfer the load from the weight of the house to dense soil layers located at great depths. The slab is an additional element that evenly distributes the load between all piles and absorbs vibration waves. As a rule, SPF is used for high-rise multi-storey buildings. They create a significant load on the supporting structure and vibrate strongly during operation. A powerful slab on a pile foundation, which is an enlarged version of the grillage, connects all the piles into a single support system and absorbs parasitic vibrations from the house structures.

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Cost of laying SPF

This is not the cheapest solution, but it is economically and operationally more profitable than some other traditional technologies. Without detailed calculations, no specialist will undertake to name even the approximate cost of the future structure. To roughly determine the cost, the grade of concrete, the dimensions and material of the piles, the thickness of the slab and other initial data are taken into account. It is necessary to take into account the costs of transporting building materials and operating special equipment.

House on a pile-slab foundation.

It is almost impossible to do without the services of specialists during the construction of SPF, even in private buildings; they will be needed at least at the initial (design) stage.

To at least roughly get an idea of ​​the cost, you can add up the prices for individual parts of the structure: the average cost of a linear meter of a slab foundation is up to 5 thousand rubles, a pile foundation is 3.5-4 thousand rubles (prices are indicated at the time of publication - 2017).

Read more about the correct installation and installation of pile foundations in a separate article: Installation and installation of pile foundations.

Installation

It is worth giving step-by-step instructions, using which and after taking the precautions and measures described above, the technician will be able to build a high-quality bored foundation with his own hands. So, the builder must adhere to the following actions:

So, the builder must adhere to the following actions:

• carrying out measuring and marking work - to carry them out competently, technicians prepare or order special drawings, taking into account both the territorial and technical features of the building;
• determination of the type of piles - hanging piles (which do not reach dense soil) and rack piles (pile structures resting on hard rocks), the first type is more applicable in disputed areas of soil - with a high groundwater level, with possible soil shifts and with high heaving soils in winter;
• installation of a drilling rig at the drilling point;

• drilling a well with the depth and diameter required by the technician (these two parameters are selected in advance of construction, depending on the dimensions of the building and the type of soil rocks);
• introducing a clay solution - this is necessary to prevent the process of shedding the walls of the hole, and then - the clay surface does not allow moisture from groundwater to pass through and becomes a kind of natural internal strengthening of the hole;
• slurry elements (or the same drilling products - all kinds of rocks, impurities, strata obtained during drilling) must be extracted to the surface using drilling fluid or mechanically (it all depends on the type of drilling);

• if the object is large and dimensional, and future pile elements require exceptional reinforcement, the developer uses specialized equipment to immerse the reinforcing elements to the entire depth of the already dug well (depending on the depth, this process can take place under pressure);
• after being placed in the hole, the reinforcement elements are fixed with stops, such stops can be formwork, the varieties of which we will consider below;
• after the procedures described above, the hole is filled with concrete (depending on the depth of the pile structure, concrete can be delivered using special equipment or manually, but concreting in any case should not last longer than 3 hours - this is the SNiP norm);
• further actions involve drilling and filling wells at another point according to the described scheme, further measuring actions and fastening all piles with a reinforced concrete strip foundation.