Foundations for low-rise construction are made from local building materials (natural stone, rubble concrete, red brick, etc.), and they also use monolithic concrete or prefabricated concrete and reinforced concrete blocks.

The plane of the lower part of the foundation is called sole(Fig. 3.1), its broadening is pillow, and the horizontal plane of the upper part of the foundation is with a sawn-off shotgun. In the absence of basements and large pits, shallow foundations are usually designed, the base of which is located at a depth of at least 0.5 m from the ground level. On soils that swell when frozen, the depth of the base of the foundation of the external walls is taken to be at least 0.2 m below the thickness of the freezing layer.

There is a certain relationship between the architectural and planning solution of a low-rise building, the design of the foundation and the condition of the soil. For example, if an architect envisions a basement, large pit, or basement in a house design, then the foundation must be of a strip structure in order to successfully serve as a basement wall. The condition of the soil can influence the choice of architectural solution for the underground part of the house. For example, if a house is placed on soils with a high level of groundwater, then the thickness of the walls of the strip foundation increases due to additional waterproofing elements, which leads to a slight reduction in the area of ​​​​the underground premises. In addition, there may be a threat of the basement part along with the house or part of the house with the pit rising (“floating up”) under the influence of groundwater pressure. In this case, it is usually necessary to abandon the design of underground premises or to design an expensive foundation structure with anchors in the ground or a weighted floor of the underground premises.

The most important parameter on which the shape and volume of foundations depend is foundation depth.Foundation depth- Thisdistance from the ground surface to the base of the foundation.

The depth of foundations depends on many factors: the purpose of the building; its space-planning and design solutions; magnitude and nature of loads; quality of the base; surrounding buildings; relief; accepted foundation designs and methods of construction work. However, first of all, the depth will determine the quality of the foundation soil, groundwater level and soil freezing.

The minimum foundation depth for heated buildings is usually 0.7 m for external walls and 0.5 m for internal walls.

The practice of operating low-rise residential buildings with shallow foundations has shown that soils that swell when frozen gradually push such foundations out of the ground. Over the course of several years, a house can rise above ground level by tens of centimeters, while different sections of the building usually rise by different amounts, which leads to skewing of windows, doors and even breaking of walls. This phenomenon occurs from the action of lateral friction forces of swelling soil on the surfaces of foundations, which exceed the resistance of the relatively small mass of the house. To neutralize the undesirable effect of swelling when the soil freezes, it is necessary to design houses without basements on shallow foundations with a base in the form of a sand cushion. When installing a sand cushion, the soil is removed to a depth below freezing of at least 0.2 m and the excavation is filled with coarse sand, poured with water and compacted layer by layer. Backfilling is carried out to a level of 0.5 m from the site planning level. Shallow foundations are installed on the artificial foundation obtained in this way. This technique allows you to achieve significant savings in materials and costs. For example, in the Kyiv region, the depth of soil freezing is 0.9 m, therefore, a shallow foundation will be 1.1 m high, and with a sand cushion - 0.5 m, i.e. with a sand cushion on soils that swell from freezing, about 50% of the material for constructing the foundation is saved.

According to the method of construction, foundations can be industrial or non-industrial. In mass construction, industrial foundations are used, which are made from prefabricated large-sized concrete or reinforced concrete elements. These foundations allow work to be carried out without seasonal restrictions and reduce labor costs on the construction site. Non-industrial foundations can be made of monolithic concrete or reinforced concrete, as well as small-sized elements (brick, rubble stone, etc.). Foundations of this kind are used, as a rule, for non-standard buildings.

By the nature of their work, foundation structures can be rigid, working only in compression, and flexible, which are designed to absorb tensile forces. The first type includes all foundations, with the exception of reinforced concrete ones. The use of flexible reinforced concrete foundations that can withstand bending moments can dramatically reduce the cost of concrete, but sharply increases the consumption of metal.

According to the structural design, foundations are divided into strip, columnar, pile and solid.

Install under all load-bearing walls of the building strip foundations in the form of solid walls. They can serve not only as a load-bearing structure that transfers permanent and temporary loads from the building to the foundation, but also as an enclosing structure for basement premises.

Strip foundations they are installed under all main (load-bearing and self-supporting) walls, and in some cases under columns. They are strip-walls sunk into the ground with a rectangular or stepped cross-section.

Strip foundations have become widespread in residential construction for buildings up to 12 floors, built using a frameless design.

The shape in plan and section, as well as the dimensions of the strip foundation, are set so as to ensure the most even distribution of the load on the base. The size of the foundation base is determined by calculation depending on the mass of the above-ground part, the foundation material and the bearing capacity of the soil. The thickness of its wall is determined by calculating strength and depending on the technological features of the material, for example, a wall made of rubble concrete is made at least 0.35 m thick, depending on the size of the filling stones. It is necessary to ensure that the resultant of all loads from the building passes in the middle third of the width of the base of the foundation, i.e. e< 1/3 (рис.3.3). Этим самым исключается появление в фундаменте растягивающих усилий.

Depending on the magnitude and direction of the design loads, strip foundations can be symmetrical or asymmetrical (Fig. 7.3).

Fig.7.3. Strip foundations: a – plan and section of a strip foundation made of prefabricated concrete blocks for a building with a basement; b, c – options without a basement made of solid and hollow blocks; d, e, f – design of a rigid foundation with a minimal, normal and maximally widened base; g – asymmetrical foundation; and – transition from one foundation depth to another; k, l, m, - options for strip foundations made of monolithic concrete, rubble concrete and rubble; 1 – basement wall blocks; 2 - hollow wall blocks of basements; 3 - foundation pillows; 4 – walls; 5 – floors; 6 – basement floors; 7 – blind area; 8 – concrete foundation; 9 – rubble concrete foundation; 10 – rubble foundation; 11 – floor of the first floor.

For the manufacture of strip foundations, any building materials except wood are used. On rocky soils, monolithic concrete with the inclusion of rock fragments (rub concrete) is more often used. This material better fills uneven surfaces of the rock base. Rubble stone foundation strips are characterized by lower cement consumption, but are more labor and material intensive. Due to the size of the stones, according to the standard, the minimum width of the strips is taken to be no less than 0.5 m. As a rule, the walls of strip foundations made of these materials for low-rise buildings do not have widening in the area of ​​the soles. Strip foundations made of red brick are designed for dry, strong soils with a thickness of 0.25 - 0.51 m. It is better to make the brick foundation pad from monolithic reinforced concrete with a thickness of at least 0.1 m, which increases the durability of the structure.

In mass construction conditions, strip foundations are usually erected from prefabricated concrete or reinforced concrete elements. Prefabricated strip foundations are assembled from two types of blocks (Fig. 7.4) - foundation pillow blocks (FBP) and wall blocks (FSB). The latter are made solid from lightweight concrete (γ ≤ 1600 kg/m 3) or hollow from heavy concrete (γ > 1600 kg/m 3), which can be used for internal walls and for external ones in soils not saturated with water. Wall blocks are used in the following sizes: height 0.6 m, length up to 2.4 m and width 0.3, 0.4, 0.5 and 0.6 m.

Fig.7.4. Prefabricated strip foundations: a – foundation design for weak soils; b – laying foundation blocks with dense soils and low loads; c, d - foundations of large-panel buildings; d – elements of prefabricated large-block concrete foundations; f, g – elements of large-panel foundations.

Installation of prefabricated concrete foundations is carried out using cement mortar and bandaging the seams. In case of weak soils, reinforced distribution belts are laid along the foundation pads and along the edge of the foundation (Fig. 7.4 a). For dense soils and light loads, foundation pads can be laid at intervals (Figure 7.4 b). The gaps should be filled with soil.

For low-rise buildings with low loads and strong foundations, when strip foundations are irrational, they are used columnar foundations. They are installed under all load-bearing and self-supporting walls, as well as under individual pillars and columns.

Columnar foundations are foundations consisting of pillars sunk into the ground and foundation beams resting on them, which take the load from the walls and transfer it to the pillars.

The pillars are installed at the intersections of the walls and in the spaces between them with a certain pitch, which is determined by calculation depending on the mass of the building and the bearing capacity of the soil. For low-rise buildings, the pitch of the foundation pillars is 2.5 - 3.0 m.

Structural options for foundation beams and their proportions depending on the pitch of the pillars are shown in Fig. 7.5. To eliminate the possibility of displacement of the foundation beam and the wall located on it due to soil heaving, a cushion of sand or slag 0.4 m thick is placed under the foundation beam.

Fig.7.5. Structural diagrams of foundation beams for columnar foundations: a – fragment of a general view of the foundation; 1 – wall; 2 – foundation beam; 3 – pillars; b – f – various types of foundation beams; 4 – prefabricated reinforced concrete; 5 – prefabricated reinforced concrete lintels (reinforced beams); 6 – monolithic reinforced concrete beam; 7 – ordinary reinforced brick beam; 8 – reinforced brick beam with steel frames in the vertical joints of the masonry.

Pillars with a square cross-section in diameter are made from prefabricated concrete blocks, monolithic concrete, red brick, and natural stone. The dimensions of the pillars are taken based on strength calculations (material and soil). For low-rise residential buildings, the size of the pillar cushion does not exceed 1 m, and the horizontal section of the pillar can be equal to the size of the base or be smaller. In the latter case, the height of the pillow is taken to be no more than 0.3 m.

In cases where it is necessary to transfer significant loads to soft soil, pile foundations .

Pile foundations are foundations consisting of reinforced concrete, concrete or metal pile rods immersed in the ground, caps - the upper widened end of the pile, and a grillage that combines the work of all piles

Pile foundations are used on weak compressible soils, with deep occurrence of strong continental rocks, heavy loads, etc. Recently, pile foundations have become widespread for conventional foundations, because... their use provides significant savings in excavation volumes and concrete costs.

According to the material, piles can be wooden, reinforced concrete, concrete, steel and combined. Depending on the method of immersion in the ground, driven, driven, shell piles, drilled and screw piles are distinguished (Fig. 7.6).

Driven piles immersed using pile drivers, vibrating hammers and vibrating pressing units. These piles are most widely used in mass construction. In cross-section, reinforced concrete piles can be square, rectangular or hollow round: ordinary piles with a diameter of up to 800 mm, and shell piles - over 800 mm. The lower ends of the piles can be pointed or flat, with or without widening, and hollow piles can be with a closed or open end and with a camouflage heel (Fig. 7.6 d).

Driven piles arranged by filling pre-drilled, punched or stamped wells with concrete or another mixture. The lower part of the wells can be widened using explosions (piles with a camouflage heel).

Bored piles They differ in that ready-made reinforced concrete piles are installed into the well and the gap between the pile and the walls of the well is filled with cement-sand mortar.

Depending on the nature of the work in the ground, two types of piles are distinguished: rack piles and hanging piles. Rack piles , cutting through the thickness of weak soil, their ends rest on strong soil (rock) and transfer the load from the building to it. They are used when the depth of solid soil does not exceed the possible length of the piles. Foundations on rack piles practically do not give rise to precipitation.

If solid soil is located at a considerable depth, use hanging piles , the bearing capacity of which is determined by the sum of the resistance of friction forces on the side surface and the soil under the tip of the pile. Pile foundations in plan may consist of:

single piles - for individual supports (Fig. 7.6 d);

strips of piles - under the walls of a building, with piles arranged in one, two or more rows;

bushes of piles - under heavily loaded supports;

continuous pile field - for heavy structures with loads evenly distributed throughout the entire building plan.

Fig.7.6. Pile foundations: a – plan and sections; b – types of piles depending on the design scheme – rack piles and hanging piles; c – elements of a pile foundation: 1 – grillage; 2 – criminal; 3 – pile; d – types of piles: 1 – four driven concrete and reinforced concrete piles – square, round, solid and hollow; 5.6 – printed regular and with a widened heel; 7, 8 – camouflage; 9 – with hinged opening stops; 10 – prismatic pile; 11 – pile-shell; 12 – pile in the leader well; 13 – wooden pile; 14 – screw pile; d – arrangement of piles: pile rows, pile bushes, pile field; e – option of a pile foundation without grillage; g, i – options for pile foundations without grillages and caps: 1 – cap; 2 – pile; 3 – base panel; 4 – floors; 5 – column; 6 - crossbar

For low-rise construction, short reinforced concrete driven piles are used, usually with a square section of 150 × 150 mm, 200 × 200 mm, or drilled piles with a diameter of 300, 400 mm or more. The depth of laying short piles is no more than 6 m.

The distance between the piles and their number are determined by calculation. Typically, the distance between hanging piles is taken to be (3 – 8)d, where d is the diameter of a round pile or the side of a square pile. The clear distance between shell piles must be at least 1 m.

Grillage beams have much in common with foundation beams. The same materials are used for their manufacture. There are two types of reinforced concrete grillage - monolithic and prefabricated. Its width is 250 × 250 or 300 × 300 mm, height – 400 – 500 mm.

Pile foundations are 32–34% more economical than strip foundations in terms of cost, 40% in terms of concrete costs and 80% in terms of the volume of excavation work. Such savings make it possible to reduce the cost of the building as a whole by 1–1.5%, labor costs by 2%, and concrete consumption by 3–5%. However, steel costs increase by 1–3 kg per m2.

In cases where the load transferred to the foundation is significant and the foundation soil is weak, arrange solid foundations under the entire building area. They are usually built on heavy heaving and subsidence soils.

Solid foundations are foundations in the form of rigid solid beam or beamless concrete or reinforced concrete slabs, arranged under the entire area of ​​the building.

Such foundations well level all vertical and horizontal movements of the soil.

The ribs of the beam slabs can face up or down. The intersections of the ribs are used to install columns in frame buildings. The space between the ribs in slabs with the ribs up is filled with sand or gravel, and a concrete screed is placed on top. Concrete slabs are not reinforced. Reinforced concrete reinforced according to calculation. If solid foundations are deeply buried and there is a need to ensure their greater rigidity, the foundation slabs can be designed with a box-shaped section and placed between the ribs and ceilings of the boxes of the basement rooms (Fig. 7.7).

Solid foundations are especially appropriate when it is necessary to protect the basement from the penetration of groundwater at a high level, if the basement floor is subjected to high hydrostatic pressure from below.

A solid foundation slab for low-rise buildings is designed only in cases of construction of buildings on soils with uneven settlement or swelling and with a high level of groundwater (in buildings with a basement). The slab is made of monolithic heavy reinforced concrete with a thickness of at least 100 mm. The thickness of the slab is determined by calculation depending on the mass of the building, the strength of the soil and the distance between the walls. For houses without a basement, the foundation slab is installed on a sand cushion, which reduces the uneven settlement of the soil. In buildings with a basement, the foundation slab simultaneously serves as the base of the floor.

Slab foundations are quite expensive due to the large volume of concrete and metal consumption for reinforcement.

On soft soils, characterized by increased compression, the best option for foundation of a house is a solid foundation. The beginning of construction work on the construction of a house is associated with determining the quality of the soil at the construction site, the depth of groundwater, the level of freezing and the material from which the construction will be carried out. In addition, it is necessary to determine the number of storeys of the building, because the load exerted directly on the base of the house depends on this. The construction of a solid foundation is necessary in cases where the load on soft soil is quite large. Such a foundation is a monolithic concrete slab located under the entire area of ​​the building.

Features of a monolithic foundation

The main feature of a solid monolithic foundation is that it can withstand a high degree of load, since the slab is made using a reinforced frame that occupies the entire area of ​​the building. Such a base has a flat, smooth surface and therefore can serve as a basement floor.

To install a solid foundation, it is necessary to erect formwork and allows construction to be carried out on any soil.

Even moving soil is incapable of damaging the integrity of the structure, and the evenly distributed load makes it possible to erect buildings on such a foundation, both the lightest and the heaviest, consisting of two or more floors.

Installation of a solid foundation is justified when carrying out construction work on buildings:

• on soil with a high sand content;
• in wetlands;
• on subsidence and peat soils.

A solid foundation is also irreplaceable in areas where a characteristic feature is the presence of soil close to the surface.

The use of a solid foundation is necessary when constructing buildings in soils prone to significant swelling. A slab made of reinforced concrete is located over the entire area of ​​the building being constructed and does not lose its strength and shape, moving, if necessary, along with the soil.

Work on the construction of a solid foundation

First of all, before starting work, you will need to perform a calculation to determine:

• slab thickness;
• slab laying depths;
• total base area.

In order to significantly increase the strength of the building, the area of ​​its base is increased by one or even two meters in each direction. When performing calculations, it is necessary to take into account the bearing capacity of the soil and the increase in load due to interior walls, ceilings, installed furniture and equipment. To obtain more accurate results, add 150 kg/m2 to the weight of the building itself, then the resulting number must be divided by the area of ​​the house. The brand of cement used to prepare concrete is also taken into account.

M500 grade cement makes it possible to obtain a composition that, when hardened, can withstand a load of 500 kg/m2; accordingly, the thickness of the base slab will be at least 50 centimeters.

Using reinforced concrete slabs, builders receive a reliable and durable foundation for light frame structures and heavy multi-story buildings.

Installation of a solid foundation

Pouring a monolithic slab

Reinforced concrete solid foundations are erected in several stages:

• marking the site intended for construction;
• erection of formwork;
• installation of reinforcement frame;
• pouring concrete.

To build a small house of a regular shape, you can use ready-made reinforced concrete slabs, but if the project of the future building is drawn up taking into account the wishes of the owners and the house has non-standard shapes and sizes, then it is necessary to pour concrete in accordance with the available data.

Marking

Before you begin marking the site, you should carefully prepare the site, getting rid of debris and vegetation. Then you need to use a level to achieve a perfectly flat surface on which the markings will be carried out. Transferring the plan of the future house drawn up according to the project to the surface of the earth requires the use of special marks, pegs, and laces. The construction thread should not be made of nylon. A stretchable cord is not able to maintain its shape and size, which means that the markings made will be inaccurate. Watch the video on how to mark the foundation.

After the pit is ready, a sand and gravel cushion is placed at the bottom, which must be thoroughly compacted. Trenches are laid across the future foundation over its entire area, the bottom of which is lined with geotextiles, and then covered with gravel and crushed stone. This is necessary drainage.

Formwork and frame

The formwork for a solid foundation is placed, protruding beyond the pit by 20 cm along the entire perimeter. The bottom of the pit is covered with a layer of crushed stone, the thickness of which must be at least 20 centimeters, and a solution based on a cement-sand mixture is poured on top of it, performing the first screed and creating a flat surface. It is covered with rolled waterproofing materials and the construction of formwork begins. Along the entire perimeter of the pit, supports are dug in for boards or panels, from which the formwork will be erected. The work is carried out under level control. Watch the video on how to install formwork for a solid foundation.

A reinforced mesh is laid on the surface of the first screed, rods are installed vertically at a distance of 20 cm, to which the lower mesh and, later, another upper mesh are tied.

The structure is fastened using annealed wire. The use of welding will lead to the formation of bridges that promote the development of corrosion.

Pouring concrete

When starting the final stage of work, you must remember that to create a reinforced concrete slab, you can order a ready-made solution, or you can prepare it yourself. But the hardening time is only 3-5 hours, and therefore you may not have time to prepare the concrete yourself. Therefore, it is worth spending money and ordering a mixer with ready-made concrete. The supplied solution is distributed over the base area using a rule, and then compacted using a vibrator.

There should be no metal components visible above the surface of the finished slab, so using a level, even before pouring begins, the height corresponding to the thickness of the foundation is marked on the vertical rods.

Solid foundations in the form of monolithic reinforced concrete ribbed or beamless slabs, they are installed under the entire building in cases where there is a significant load on the foundation, and the foundation soils are very weak, with uneven subsidence, or when it is necessary to protect the basement from the penetration of groundwater at a high level.

To transfer significant loads from buildings or structures in weak soils, they arrange pile foundations. Pile foundations make it possible to increase the level of industrialization of construction work. In recent years, they have found increasing use in construction on natural foundations.

According to the manufacturing method, a distinction is made between piles driven into the ground by impact, vibration, screwing, and in the form of a monolithic structure, concreted on site in specially prepared wells (cast-in-place piles). Depending on the nature of the work, a distinction is made between hanging piles and continental piles (rack piles).

Hanging piles are appropriate when the depth of solid (continental) soil is significant, and the soil resistance at the side surface of the piles and under the lower ends is sufficient to withstand the transmitted load (Fig. 1. a).

If the depth of solid soil does not exceed the possible length of the piles, rack piles are used, which with their ends enter the continental soil and transfer the load to it (Fig. 1. b).

Rice. 1. Pile foundations a - hanging pile; b-pile-rack; c-reinforced concrete piles; g-rammed concrete; d-metal screw-on; 1 - reinforced concrete pile; 2 - prefabricated reinforced concrete grillage; 3 - concrete filling; 4 - wall panel; 5 - weak soil; 6 - dense (continental) soil; 7 - blade. 8 - joint

Depending on the material, piles can be wooden, reinforced concrete, concrete, steel or combined (Fig. 1. c-d).

Piles under the base of the foundation are usually placed in groups or rows. Single piles are those placed in isolation or at a distance of more than 1/4 of their length.

A group of piles located under the foundation is called a pile bush, and piles located in one or more rows form a pile strip. The upper ends of the piles are combined into a single structure using a concrete or reinforced concrete slab - a grillage (Fig. 1. a, b).

Blind areas or sidewalks are used to remove precipitation from the foundation and plinth.

The article describes the features of solid slab foundations. The scope of their application, operational and design differences are discussed in great detail. Applied issues related to the technology of construction of foundation slabs are brought to the fore.

This is a continuation of the series of articles about foundations, and we have already published a lot of interesting material. Therefore we recommend:

A slab foundation, also known as “solid”, also known as “floating”, or “Swedish, Scandinavian slab”, is a solid slab located under the entire area of ​​the building, buried in the ground, or laid on it. There are several design options for slabs - box-shaped, flat, ribbed, prefabricated from road reinforced concrete products, monolithic, with extensions at the corners, with or without reinforcement, insulated and cold... They all have their own distinctive features and specific scope of application. For private suburban construction, in terms of economic and functional characteristics, flat monolithic reinforced concrete slabs with a thickness of 20 to 40 cm with insulation have proven themselves to be the best. We will talk about them further.

Why choose a slab foundation

In low-rise construction, which is what we are actually interested in, this type of foundation for many reasons will be preferable to its competitors (both strip and pile structures). This is explained by advantages of both a purely technical and construction-related nature.

Strengths of solid foundations

Universality in foundation geology. A floating structure can be correctly used on all types of soils, including weak-bearing, heaving, horizontally mobile, high groundwater levels, permafrost...

There are some restrictions on the terrain - it is difficult to build such a foundation on a slope; most likely, piles will be preferable. However, there are American-tested technologies for constructing slabs on hillocks, which in their design (in the lower part of the site) have elements of high monolithic strips. Another “centaur” suitable for such places is a pile foundation with a low grillage in the form of a monolithic slab.

Good load-bearing capacity. This quality is due to the specific mechanics of the “house/slab/soil” interaction. In the next chapter we will look at this point in detail. In short, the slab has a large support area, so the pressure on the foundation soil is very low (from 0.1 kgf/cm2). Consequently, a two-story stone house on a slab can be built with confidence. They say that the elevator shaft of the Ostankino Tower stands on a monolithic slab.

High spatial rigidity. It is due to the absence of seams and joints, the use of rigid reinforcement, the massiveness of the structure and high material consumption. The slab foundation is excellent for houses with “inelastic” walls, which are very afraid of even the smallest (1–3 mm) movements of the supporting structure - brick, aerated concrete, cinder block, shell rock and other mineral materials.

In the presence of excessively heaving soils and significant sensitivity of buildings to uneven deformations, it is recommended to build them on shallow and non-buried monolithic reinforced concrete slabs, under which cushions made of non-heaving materials are placed.

SP 50–101–2004 “Design and installation of foundations and foundations of buildings and structures.”

Good insulating properties. When properly executed, it does not allow water to pass through and prevents heat loss through the floor.

Simple construction technology, built quickly. Easy to mark, minimum excavation work, simplified formwork design, easy to reinforce and concrete. Can be manufactured by low-skilled builders.

Conditional disadvantages of a slab foundation

Technically, it is very difficult to combine a solid slab and a basement in a structure.

The slab can be poured only in favorable weather (it is slightly inferior to prefabricated and pile driven foundations).

High price. Increased material consumption (concrete, reinforcement), of course, leaves its mark. But if you look at the problem as a whole, the picture changes dramatically - we save a lot on other materials, construction stages, and production operations:

• the slab becomes the subfloor of the first floor - no need to make an overlap;
• You can lay a water heated floor in the mass of the slab, rather than pouring a separate screed for it;
• for the manufacture and fastening of formwork panels, less boards or sheet materials are needed (at least twice as much as strip structures);
• no need to pay for removal/planning of a large volume of selected soil;
• the height of the external walls is reduced, since it is possible to obtain a lower base (and these are expensive facade finishing materials, labor costs...);
• lifting equipment, concrete pumps, excavators, driving pile drivers, drilling machines are not needed, everything is limited to mixer vehicles;
• you can build it yourself and not hire highly paid professional builders, there is less risk of suffering financially from the “human factor” (simpler technology).

It turns out that the main disadvantage of slab foundations is the low awareness of domestic developers about their advantages. But in the northern part of the USA and Scandinavian countries, monolithic slabs have become the No. 1 foundation.

The principle of operation of a slab foundation

Situation

The building density is growing, people increasingly have to build on “bad” soils (weak, constantly wet, heaving, frozen...).

Modern projects of country houses have become much more complex in terms of architectural and planning solutions: different parts of the building are built at different heights (options of one and a half floors, attached garages, special solutions for staircases and landings...), uneven distribution of load-bearing walls over the building area. Houses are now bigger, higher, heavier.

Problem

On top of the foundation and on the natural foundation there are uneven impacts from the house. From below, complex soils either tend to form local failures under the building, or forces of frost heaving push the building out, and then, when thawed, sag. There is a danger of deformation and destruction of supporting structures.

Solution

Increase the supporting area of ​​the foundation, reducing the load from the house on the natural foundation.

Maximize the spatial rigidity of the foundation and evenly redistribute the pressure from top to bottom.

Use a heat insulator to separate the heated rooms from the ground under the house - thus eliminating uneven freezing under the building (in winter, the ground under the slab does not thaw).

All these methods of dealing with “unevenness” are inherent in the principle of operation of an insulated monolithic slab. This is a kind of single platform under the house, which is not subject to local bending (if properly designed), and without deformation is able to actually move with the ground - “float”.

Features of designing a slab foundation

Slab design differs significantly from methods for developing other types of foundations. Here, engineers also take into account all the main soil parameters and all loads (weight of structures, operating weight, snow pressure). SP 20.13330.2011 has not been canceled.

However, the slab foundation must be considered as a single, jointly working “slab-above-foundation part” structure. Therefore, in this case, special attention is paid to a detailed study of specific components of the building and the supporting structure as a whole; drawings of the house are created and calculated, indicating diagrams of load distribution and their directions.

The whole problem lies in the difficulty of competently modeling bending loads, possible rolls that the slab experiences, and, accordingly, calculating its thickness, configuration, and the need for reinforcement, including local reinforcement. The most efficient design of foundation slabs is carried out using special computer systems that produce very detailed working drawings. That is why we recommend ordering a foundation slab calculation from a specialized organization; the cost of such work will range from 5 to 10 thousand rubles.

The most widespread are slabs with a thickness of 20 to 40 cm, but one detail is very interesting: most calculations show that different slab thicknesses can be used for the same house if the percentage of reinforcement is correctly manipulated.

For example, a solid foundation for some abstract building. At 20 centimeters, it is necessary to carry out local “additional reinforcement” of especially loaded areas and not make mistakes in the calculations; at 25 centimeters, the frame can be knitted evenly, without particularly risking. But a 30-centimeter slab, when compared with a 25-cm structure, will not allow you to save on reinforcement, but it will use much more concrete.

Exceptionally competent calculation allows you to cast slabs even with a thickness of 15–18 cm.

Note that it is possible to significantly increase the resistance of the slab to punching, while reducing its overall thickness (read material consumption) by making local thickenings of the foundation in the area of ​​the corners, the junction of load-bearing walls, along the entire perimeter, under the columns. Such reinforced slabs are often called “American”; in cross-section they look like a prism.

The slab foundation cannot be smaller in area than the house; all cantilever sections must be taken into account. For example, if the building will be faced with brick or other heavy materials, then the slab must be laid in large sizes to provide a supporting area for the cladding.

Slab foundation construction technology

Since slab foundations are often used in very difficult geological conditions, the most stringent requirements are imposed on the planning and construction of floating structures, which are stipulated by many regulatory documents, for example, SNiP 3.03.01–87 “Load-bearing and enclosing structures” or SP 50–101– 2004 “Design and installation of foundations and foundations of buildings and structures.” Naturally, only high-quality materials should be used for the construction of foundation slabs.

The construction of all solid foundations is carried out approximately according to the same scheme:

• Design.
• Marking (only the outlines of the building are taken into reality).
• Removing turf, sampling soil (if cushion/drainage is necessary).
• Laying buried communications (water, sewerage).
• Installation of cushion and drainage.
• Installation of hydro- and thermal insulation.
• Assembling a “warm floor”.
• Knitting and laying of reinforcement cage.
• Assembling and unfastening formwork.
• Concreting.
• Stripping.

Let's look at these operations in more detail.

We have more or less figured out the design. If you are building something serious, it is better to order the development of a foundation project from engineers, and you will definitely save your nerves and money.

We have already discussed the issues of carrying out preparatory work and carrying out markings in situ in the article “Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement.”

As for earthworks. If soil replacement (massive cushions) and insulation are not required, then it is enough to remove only the top fertile layer, otherwise, the soil of the natural foundation is removed in the required volume. Sometimes, before excavation, it makes sense to level the building area - to make bedding. Then the additional material is very carefully compacted with a vibrating plate.

The most important condition is that the bulk soil under a slab foundation should not be inferior to the mainland (natural) in any way.

There is no need to worry that it will be difficult to maintain communications under the slab. Everything is done as usual: where there will be a technical room, a pit is always made in the slab for entering communications (foam is laid near the pipes, or a contour is made from formwork), the smaller it is, the better for the rigidity of the foundation. In any case, the pipes cannot be sealed tightly. Under the slab, communications run in a trench and are covered with drainage materials. Read about drainage of communication lines in the article “How to make drainage on a site.”

The cushion is an artificial base, it is designed to replace “bad” soils. The material for the cushion is most often a mixture of sand and crushed stone, which have good drainage properties, have little compression, and do not heave. The sand and gravel cushion is laid in layers of 100 mm, and each layer is carefully compacted with a vibrating platform. If clean sand is used, it must be spilled with water.

It is necessary to periodically check the horizontalness of each layer of pillows.

In areas with unfavorable water balance, it is recommended to lay several drains under the slab (cushion) to drain water.

Most technological maps for the production of solid foundations suggest laying geotextiles under the cushion, which prevents sand and gravel from silting (read: losing properties that are important to us).

In order for the hydro- and thermal insulation to fit well and not be deformed by the mass of concrete, the upper part of the cushion must have the most even plane possible. Some manufacturers of floating foundations even prefer to make a preparation screed from sand concrete.

The cushion is covered with a thick polyethylene film or other waterproofing materials that will prevent laitance from leaking during concreting. The sheets are laid overlapping and glued/soldered.

A layer of insulation up to 100 mm thick is laid on the waterproofing. Previously, they used polystyrene foam, but now everyone has switched to extruded polystyrene foam. Some builders believe that insulation is not a necessary layer, but it reduces heat loss through the slab and does not allow the soil under the slab to thaw uncontrollably and unevenly even under heated rooms. If you want to use a warm floor, you will not heat the ground, but let all the heat into the house. In the technological maps of foreign companies, it is recommended to lay the insulation (and pillow) outside the slab.

Heated floor pipes are laid out directly onto EPS sheets using a special mesh; naturally, they are not insulated with any materials in order to better transfer heat. Some heating routes can also pass through this layer - they are carried out in sleeves and heat insulators. All ends are removed from the pit for communications, the system is ringed and crimped. Under pressure, air pumped into the pipes prevents them from deforming when pouring concrete.

Reinforcement is perhaps the most difficult operation in the construction of floating foundations. This is where the most mistakes are made, both technological and design.

Let's start with the main thing. According to SP 52–103–2007, the minimum percentage of reinforcement for a reinforced concrete slab is 0.3%. It is calculated as follows: take a cross section of the slab and calculate its area, calculate the total cut area of ​​all reinforcing bars, and compare these indicators. If the metal content of concrete is insufficient, then increase the diameter of the reinforcement or the number of rods (reduce the pitch). For thick slabs, a third tier of metal is used, located in the thickness of the slab. Practice shows that most often it is enough to lay two layers of reinforcement with a diameter of 12–14 mm, and a pitch of 150–250 mm.

Do not forget that in loaded areas (columns, load-bearing wall inside a building...) additional reinforcement may be required by laying auxiliary longitudinal rods within the punching prisms.

Depending on the design of the building, it sometimes makes sense to install vertical reinforcement outlets under load-bearing walls and columns (SP 52-103-2007), which will provide additional rigidity to the “slab-above-foundation part” system.

The presence of a protective layer of concrete is a prerequisite for high-quality reinforcement. The reinforcement cage meshes are displayed on special polymer mushroom stands. The fungi of the lower tier are small, about 4–5 cm. The intermediate fungi (between two meshes) have a height depending on the thickness of the slab, so that about 5 cm of concrete (protective layer) remains above the upper reinforcement. The fungi are placed one above the other, their total number (step) should ensure sufficient resistance of the frame to the loads arising during concreting.

It is prohibited to use all kinds of linings made of wood, stone, and metal.

It is recommended (SP 63.13330.2012) to connect the ends of the frame, the upper and lower tier, with U-shaped elements made of reinforcement. The reinforcing bars should not come into contact with the formwork, since a protective layer of concrete with a thickness of at least 40 mm should be provided.

A frame of viscous reinforcing bars is made using wire. The use of electric arc welding is allowed, but then it is necessary to use class A500c fittings, or similar, with the index “C”.

Due to the large volume of reinforcement work, it may be advisable to use standardized factory-made welded mesh. The joints obtained after laying must be placed in a “checkerboard” order - the joints of the finished mesh of the lower tier of reinforcement must be overlapped by the entire mesh of the upper tier.

The floating foundation formwork is very easy to assemble; you just need to level each side of the perimeter. Please note that a lot of concrete is used, and the pressure on the shields will be quite serious - so lift them off the ground very well.

The formwork should be wrapped inside with polyethylene to prevent laitance from leaking through the cracks. As an option, you can lay EPS sheets near the formwork, then they will reliably “stick” to the concrete and provide vertical insulation of the slab.

Expanded polystyrene is also used to separate buildings adjacent to the house, which require their own foundation (garage, porch, terrace...).

A separate small formwork contour is made for the pit for communications.

You can read about formwork and reinforcement in the article “Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement.”

The nuances of making a monolith can be found in our publication “Strip foundation. Part 3: concreting, final operations.”

Concreting must be done in one work shift. The most rational way would be to order the delivery of concrete with a mixer and pour the foundation directly from the tray. For concreting remote areas, you can use a homemade gutter.

Concrete must be compacted with an in-depth vibrator.

For the manufacture of slab foundations, concrete is used with characteristics that are regulated by SP 52–103–2007. Most construction companies producing floating foundations offer to order concrete with the following performance properties:

• strength class from B22.5 (grade not lower than M300);
• water resistance coefficient from W8;
• frost resistance from F200;
• mobility P-3;
• possibly sulfate resistant if groundwater is high.

Taking into account domestic realities, it is better for a private developer to order concrete at least a grade higher than the standardized one - there will be a greater chance of obtaining the design strength class.

Next, you should carry out manipulations to care for the concrete. When the slab reaches 50% strength, the formwork can be removed. We examined these works in detail in the article “Strip foundation. Part 3: concreting, final operations,” we will add that the next day after pouring the floating foundation, the upper plane of the slab should be rubbed down - this will be a good base before installing any floor coverings.

In Northern Europe and the USA, floating foundations have been actively used for more than half a century; over time they have proven their reliability, functionality and economic attractiveness. In our country, the slabs also found their developer. From year to year, solid foundations are becoming more and more popular, since in many cases there is simply no alternative to them.

Turishchev Anton, rmnt.ru

http://www. rmnt. ru/ - RMNT website. ru

How to make a solid foundation? Solid foundation

Solid slab foundations - construction

A solid foundation is a representative of the shallowly buried type and is a solid slab base. The depth of its occurrence should not exceed 50 cm. The foundation slab is capable of absorbing various loads without deformation due to the rigid reinforcement of all structures.

Application area

slab foundation

The use of a solid slab foundation is relevant in the following cases:

• arrangement of the base for technological equipment, implying possible movement if reconstruction or modernization is necessary;
• when building on soil with low bearing capacity, in this case the use of a strip foundation is impractical;
• if uneven settlement of the building may occur, in this case the loads are redistributed so that they are displaced from the ground, which has weak load-bearing abilities;

Advantages and disadvantages

The main disadvantage is the high costs; the construction of such a foundation will require a large amount of concrete and reinforcement. As for the advantages over other types (for example, pile foundations), there are several:

• ease of installation;
• protection from melt and groundwater of the entire structure;
• load-bearing capacity is at the highest level;
• the ability to prevent horizontal and vertical displacement, as well as soil heaving.

If the soil on which the building is being erected is particularly heaving or has very weak bearing capacity, a floating foundation can be used in such cases.

Design Features

To ensure high strength characteristics in the technological process it is necessary to use:

slab structure diagram

1. High class concrete, not less than B 12.5.
2. Steel reinforcement, the diameter of which should be in the range of 12–16 mm.
3. The increased support area will reduce the load to 0.1 kgf/cm².
4. Additional cross stiffening ribs that will provide the necessary resistance to climatic temperature changes.

Solid foundations have proven themselves excellent in low-rise construction. This is especially true in cases where the building has basements and semi-basements, because such foundations are designed to withstand significant loads.

Since the consumption of materials is quite high, the use of a non-buried foundation will help reduce these indicators. It will reduce costs by an average of 40%. One of these options is a shallow insulating base.

Frost-resistant solid foundation

It is a justified alternative to a deep foundation and even in harsh winter conditions, a shallow depth of 50 mm will provide the necessary thermal insulation properties.

Technological features

The basis is a monolithic slab; in this case, the foundation is laid on insulation. The monolithic block should be 20-25 cm thick, with thickened edges. Polypropylene board is used as insulation. Insulation laid around the perimeter of the building retains heat and reduces the depth of freezing.

Installation problems

During installation, builders very often encounter certain negative qualities of thermal insulation material. Polystyrene foam has poor impact strength. It also decomposes when exposed to ultraviolet rays. To eliminate this problem, vinyl chloride plastic is used. It is supplied in rolls and has quite flexible properties. It can also be easily field-mounted to foam and concrete slabs.

Road slab foundation

foundation slabs photo

• there is no need to arrange formwork;
• simplicity and speed of installation;
• the foundation is not afraid of high water levels and underground flows;
• Suitable for all types of soil, including sandy soil.

Of course, there are also disadvantages - the construction of multi-storey buildings on such a foundation is unacceptable, the maximum number of floors is two.

Technology for laying a solid slab foundation

The construction of the foundation is carried out in several stages.

First stage. Preparatory work

1. Calculation and purchase of the required amount of materials.
2. Site preparation - debris is cleared and leveled.
3. Markings of the structure are applied when transferring the plan to the area.
4. A pit is being dug.
5. The formwork is being installed.
6. A sand cushion is lined and a drainage system is installed if necessary.
7. A layer of waterproofing is laid out, which can serve as a polyethylene film.

Second phase. Structural reinforcement

Reinforcement is performed with steel reinforcement. It can be connected to each other by twisting wire. Welding in this case is unacceptable, because the frame connections may be subject to corrosion.

Reinforcement must be done in two tiers. The lower level is a longitudinal structure, which is supporting and is assembled outside the foundation and, after assembly, is transferred to the immediate installation site. The height depends on the size of the foundation.

The second layer of reinforcing mesh is laid on the supporting tier. In general, the entire structure should be 3-5 cm less than the height of the base.

Third stage. Pouring concrete

The fastest way to complete this stage will be ready-made imported concrete. After all, doing such a volume of mixture yourself is a very labor-intensive process. The prepared structure is filled with concrete along the height of the sides. After which it is necessary to level the surface. All pouring operations must be performed before hardening; this interval is within 3–5 hours.

A solid foundation serves as a good foundation for any structure. Do not forget that violation of norms and rules in the technological process can lead to the destruction of the entire building structure.

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stroykirpich.com

preparatory work, frame, concrete pouring

The construction of any structure begins with laying the foundation. The foundation is the basis of the building, which serves as its support, ensures the stability, reliability and safety of the house. Modern construction knows several types of foundations, each of which is optimally suited for its purposes. One of them is a solid foundation, the structure of which is a monolithic concrete slab without empty cavities (unlike a strip foundation).

If structures with different weights will be located on a slab foundation, this should be taken into account when reinforcing, strengthening the corresponding places.

Solid slab foundations are indispensable for construction on loose soils with low bearing capacity.

You cannot do without this type of foundation when building on heaving soils, on old landfill sites or on sandy terrain. This type of foundation is shallow. If you use this type of foundation during construction, then even on a small construction site the building will receive a large support area. On this basis it is possible to build both heavy multi-storey buildings and prefabricated panel structures with low weight. However, when building structures of different weights, one significant difference must be taken into account: the location of the reinforcing rods will be different.

Calculation of basic parameters

The purpose of calculating a slab foundation is to determine the thickness of the slab, the total area and depth of the foundation. It is recommended to make the foundation area slightly larger than the area of ​​the future building. Increasing the foundation slab by 1-2 m in each direction will not greatly affect costs, but will significantly increase the strength of the structure.

When building a one-story house, the area of ​​the foundation must be related to the total weight of the building and foundation. In this case, the bearing capacity of the soil on which construction is carried out is taken into account, for example, for dry soils the bearing capacity is 2 kg/1 sq. see. When calculating, take into account that the foundation bears the load of the entire building with interior floors, the roof and even snow on the roof, which will remain there for some time. In addition, the house will contain furniture and residents, who also create a load, so you need to add 150 kg/sq.m. to the weight of the building itself. m. After receiving the weight of the future house, it must be divided by the area. Taking into account the type of soil, the parameters of the foundation are determined in accordance with the load.

When building a two-story house, the calculation scheme is the same. For example, if the calculated weight of such a house is 300 tons, and its area is 100 square meters. m., then the load per 1 sq. cm will be 300 g. If you use M500 concrete, then the thickness of the foundation can be minimal (about 50 cm), since this brand of concrete can withstand up to 150 kg of load per 1 sq. m. cm.

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Preparatory work

As a result of laying a solid foundation, a solid reinforced concrete slab should be obtained, occupying the area of ​​the entire building. The main distinguishing feature of this design is its increased load-bearing capacity, which ensures the stability of the foundation against soil displacement and helps to increase the building's resistance to loads resulting from temperature fluctuations or land shrinkage.

Laying a solid foundation slab is mandatory when building on the following types of soil:

• subsidence;
• heaving;
• weak-supported;
• water-saturated;
• swampy;
• peated.

The slab foundation is erected in several stages. First of all, the site is prepared and marked, the formwork is installed, the reinforcement frame is mounted and concrete is poured. To lay such a foundation, industrially manufactured reinforced concrete slabs of standard sizes can also be used. However, this option is not suitable for buildings of all shapes and sizes. In addition, such a foundation will not be airtight. If you still use slabs, then pay attention to the fact that they should be 20-30 cm thick.

Before laying a solid foundation, it is necessary to carry out preparatory work. The area must be cleared of debris and plants. In addition, its surface must be perfectly flat. Use a level to achieve the best result. You can level the surface with a shovel. You need to calculate in advance how much materials will be needed and purchase everything you need.

When the area is cleared and its surface is leveled, you can proceed to marking it. Marking the site involves transferring a pre-drawn plan to the area. When laying out, marks are placed in key places of the future building. The top layer of soil (up to 50 cm) must be removed, as it has a low bearing capacity and is easily pressed. This is a rather labor-intensive process, for which it is recommended to use equipment (excavator).

A cushion of a mixture of sand and crushed stone or gravel in a ratio of 2:3 is placed at the bottom of the finished pit. The pillow must be thoroughly compacted. It is necessary for the following purposes:

• the pressure of the building on the ground is distributed evenly;
• moisture contained in the soil passes under the house unhindered;
• reduces the force of frost heaving on the base of the foundation.

Trenches are laid across the future foundation to accommodate reservoir drainage. The bottom of the trenches is covered with geotextiles, on top of which crushed stone is poured. It is also recommended to place perforated plastic pipes in trenches. They must be sprinkled with granite crushed stone and protected from clogging by clay particles with geotextiles.

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Manufacturing of formwork and reinforced frames

It is necessary to install sealed rotary wells at the corners of the pit. This is due to the fact that in most cases the slab foundation stands on soils in which the moisture content is high, and groundwater is located close to the surface. After this, formwork is installed, which should extend beyond the planned foundation by 15 cm on each side.

A layer of granite crushed stone up to 20 cm thick is poured onto the bottom of the pit. A small layer of concrete (about 4 cm thick) is poured on top of this base. This concrete layer is the first screed. Before pouring it, it is necessary to fill the crushed stone with a mixture of concrete and sand to level the surface.

The next stage is waterproofing. You can use special soldered roll materials or lay regular material on bitumen mastic. At this stage, you can also lay down thermal insulation material, which will protect the foundation slab.

Next, a reinforced frame is formed from two iron meshes: upper and lower. They are connected by vertical rods, which are installed every 20 cm. All frame elements are connected with special annealed wire (knitting). Welding is not recommended, as it will create bridges that are prone to corrosion.

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Pouring the foundation slab

The final stage of work on laying a monolithic foundation is pouring concrete into the finished formwork with a reinforced frame. To prepare concrete, you can use ready-made dry mixtures, order concrete from a manufacturer, or prepare it yourself from start to finish. For concrete you will need sand, cement and gravel (or crushed stone). The concrete solution is poured into the formwork up to the height of the sides. Please note that you have about 3-5 hours before the concrete begins to harden, so this stage of work must be completed quickly. The concrete solution must be prepared immediately before pouring.

Now you know the manufacturing features that distinguish a solid slab foundation from other types of foundations. Please note that the material consumption and labor intensity of its manufacture are quite high. However, this is necessary when building on certain types of soil.

moifundament.ru

types, classification, need for use, composition, calculation and application

Foundations of different types can be erected under suburban and multi-storey buildings. For example, in some cases, solid slab foundations are poured under houses. Such grounds, in turn, can also be classified into several types. Before starting to pour a solid foundation, of course, its design must be drawn up.

Necessity of application

Slab foundations are one of the most reliable types of house foundations. In this regard, they are superior to tape and columnar ones in any case. However, the area of ​​this type of structure is very large. They are solid foundations - a single thick slab under the entire house.

The construction of such structures is, of course, very expensive. In addition, for example, when building a low-rise country house, foundations of this type, unlike others, cannot be filled with concrete using homemade means. In this case, the cement mortar has to be ordered ready-made. Liquid concrete is poured into the formwork when constructing such a foundation from a tank using a hose. And this, of course, makes the construction of the foundation even more expensive.

Due to the high cost, foundations with a solid slab are built under houses quite rarely. Their construction is considered advisable mainly only when the building is built on non-static soils. In this case, a solid slab can maintain the integrity of other building structures during movements.

Also, foundations of this type can be erected under various types of small-area buildings. For example, sometimes garden gazebos are built on such a foundation. Most often, under such structures, of course, columnar foundations are built. A solid foundation, however, in this case can also be a good solution.

The slab under the gazebo or small extension, of course, will be very small in size. If the concrete depth is shallow, it won’t take much. In addition, it will be possible to fill the slab under the gazebo without the use of special equipment and assistants - manually at a time.

Main types by filling method

When building houses, solid foundations can be erected:

not buried;

shallow;

strongly buried.

The first type of base can only be used in areas where there is no frost heaving. They build exclusively lightweight houses of small area on shallow foundations. The thickness of such structures, depending on the type of soil, can vary between 30-50 cm. Sometimes heavy brick houses are built on such foundations. But the use of non-buried foundation slabs under such structures is allowed only on rocky soils.

Shallow foundations are usually erected during the construction of small private houses. The pit under them is dug very shallow. In most cases, when pouring such a foundation on an area according to the markings, the top fertile layer of soil is simply removed. Deeply buried foundations are built only on heaving soils under heavy buildings.

Types by design

In this regard, solid foundations are distinguished:

monolithic;

lattice.

The first type of foundation is a regular concrete slab. Solid monolithic foundations are the simplest and most popular type of such structures. But on very unreliable soils, foundations with stiffeners can also be installed. The latter are poured directly under the slab.

Sometimes the ribs at the lattice bases can be directed upward. In this case, the walls of the building are erected on them using approximately the same technology as on strip foundations. When using this type of solid foundation in a building, among other things, it is possible to equip a basement. This is how deep slab foundations, for example, are often poured.

Design

When developing drawings of a solid foundation, of course, first of all you should decide on its thickness. When constructing high-rise city buildings, such calculations are made exclusively by specialists using various kinds of formulas.

In individual construction, a design for a solid reinforced concrete foundation for a small house can be developed independently. In this case, most likely, you won’t even have to calculate anything. There are standard indicators for the thickness of such foundations for certain types of buildings, which can be used as a guide in the process of drawing up a project.

So, for example:

gazebos and light extensions are erected on solid foundations 100-150 mm thick;

under light frame private houses, as well as one-story log and cobblestone houses, foundations of this type are most often poured to a depth of 200-300 mm;

under concrete structures or brick or two-story log buildings, solid foundations with a thickness of 250-350 mm are erected;

under two- or three-story houses made of brick or concrete, it is necessary to pour slab foundations at a depth of 300-400 mm.

Load collection

If you wish, of course, you can independently make a more accurate calculation of the solid foundation when building a country house. The collection of loads when pouring such a structure is determined taking into account:

constant pressure from the roof, ceilings, walls, etc.;

temporary loads - snow, furniture, people.

The permanent load is calculated depending on the materials used to assemble the building structures and their parameters. According to the standards, the mass of the walls should be taken minus the openings.

The weight of the slab itself when performing calculations of solid foundations:

not taken into account on sandy soils;

on clayey ones it is divided in half;

on quicksand it is taken into account completely.

The snow temporary load on the foundation is determined according to Table 10.1 SP. In this case, the parameter is taken for this specific area. Uniformly distributed loads for residential buildings are assumed to be 150 kg/m2. The weight of very heavy objects that are supposed to be placed in the house is taken into account separately.

Selection of materials

The collection of loads on such foundations is calculated in the same way as on columnar and strip foundations. A solid foundation, like any other, is poured in most cases, of course, from a concrete mixture. Having determined the thickness of such a foundation, you can easily calculate the amount of material required for its construction.

Concrete for the construction of solid foundations is usually used grades B15-B25. You can, of course, pour slab foundations using a higher quality and durable mortar. However, this is usually considered impractical due to the increased cost of work. One of the undoubted advantages of slab foundations in any case is increased strength.

In addition to concrete, to build such a foundation you will also need materials such as sand, reinforcing bars and waterproofing. To assemble the formwork you will need to prepare boards. According to the standards, lumber with a thickness of at least 30 mm must be used to create a pouring form for the slab base of a house. Before pouring the solution, it is recommended to cover the formwork boards with plastic film.

Concrete and reinforcement

Calculate the amount of material required to fill such a base, in addition to the thickness of the slab, taking into account the fact that:

at the edges the foundation should extend beyond the building by at least 10 cm;

the reinforcement rods for the slab should be 6 cm shorter than it;

rods are installed when pouring in increments of 40 cm;

the sand cushion should also extend 10 cm beyond the building;

When pouring, the waterproofing material is laid with a small margin.

It is advisable to use roofing felt as a waterproofing agent for pouring such a foundation.

Work order

Slab foundations are poured in several steps. A pit of the designed depth is first dug on the site.

At the next stage, when arranging a solid slab foundation, a multi-tiered reinforcement frame connected with the use of wire is installed on the sand cushion. In order for the volumetric mesh to subsequently appear in the thickness of the concrete, special plastic stands or bars 5 cm thick are first placed at the bottom of the pit.

At the final stage, concrete from the tank is poured into the pit. During the process of laying the mixture, any defects that appear are manually eliminated. From time to time, the concrete layer in the pit is pierced with shovels to eliminate air bubbles. At the final stage, carefully level the surface of the slab.

To fill a lattice solid foundation, longitudinal trenches are dug in the pit before filling with crushed stone. The concrete poured into them subsequently forms ribs.

The final stage

After the foundation is poured, it is advisable to cover the slab with plastic film. Subsequently, the slab should be periodically moistened with water for 2 weeks. This will avoid the appearance of surface cracks. It is allowed to erect walls on such a foundation, as on any other, only after the concrete has fully matured. That is, approximately 28 days after pouring.

fb.ru

Foundation of a solid structure - technology for constructing a solid foundation, construction of country houses from NPO "ANTARES Trade"

The construction of a solid foundation is most often resorted to in cases where the area allocated for the construction of a house is located on soil with a high groundwater level. Sometimes a solid foundation is used on sand cushions and on swelling soils.

A solid foundation is a single reinforced concrete slab that goes deep into the ground. In this regard, this type of foundation is often called slab foundation. It is well suited for building houses made of bricks, concrete blocks or other heavy building materials. Often, the project also provides for a solid foundation in the case of the construction of industrial premises, which are subject to increased requirements in terms of load-bearing capacity. These include, for example, garages.

Due to the uniform distribution of the load applied to the foundation over its entire plane, the pressure on the ground is minimized. This allows the construction of country houses even on swelling, unstable soils.

The foundation of a solid structure is resistant to soil movement that may occur due to settlement or freezing. Its construction is possible on almost any soil, since a monolithic slab made of concrete or reinforced concrete actually moves along with the soil when it shifts, eliminating deformation of the structure built on it.

The main technological feature of a solid foundation is the fact that it, together with the formwork, forms a single integral structure. Taking into account the fact that a monolithic foundation is most often laid on problematic soils, special requirements are placed on it. That is why, when planning and constructing it, all technologies must be followed with special care.

A solid foundation slab can be simple or reinforced, ribbed or smooth, solid or lattice. The grade of concrete is selected depending on the characteristics of the project being implemented.

In terms of depth, a solid foundation can be deep or shallow. The first, in addition to better load-bearing properties, also allows you to organize a basement.

The foundation of a solid structure is laid on a compacted gravel-sand cushion, under which a drainage system is installed. To organize a deep foundation, it is necessary to first dig a pit. Before pouring concrete, reinforcement should be installed, a waterproofing layer should be laid, and, if necessary, a layer of insulation.

antares-stroy.ru

Construction of a monolithic foundation | Solid foundation

Today, any more or less serious building, erected in accordance with current technological standards, requires a foundation. Depending on the characteristics of the soil, the number of storeys of the building and some external factors, the type of foundation used is selected.

A monolithic solid foundation is poured when a building is erected on loose soils with low bearing capacity and in places where groundwater is close to the surface. Examples of places where it is impossible to do without the use of such a foundation are old landfills, soils prone to swelling, and sandy areas. This type of foundation is classified as shallow, and its use allows the building to obtain an acceptable support area on a small plot of land. This type of foundation is quite universal - it is built both under heavy multi-storey buildings and under prefabricated panel structures of light weight. The main difference will be in the method of placing reinforcing rods and the arrangement of additional stiffeners.

Technology for constructing a solid (slab) foundation

A solid (slab) foundation is a solid slab of reinforced concrete placed over the area of ​​the entire building. It has an increased load-bearing capacity and resists soil displacement well, actually moving with the soil. It also increases the house’s resistance to loads that are likely due to land subsidence or temperature fluctuations.

General characteristics

The slab foundation is focused on complex types of soil:

• peated;
• swampy;
• water-saturated;
• weak-supported;
• heaving;
• subsidence.

Stages of work

Work on the formation of a slab (solid) foundation allows both the pouring of concrete at the construction site and the use of standard reinforced concrete slabs, which are used for laying roads. The main condition is a thickness within 20-30 cm. Depending on this, construction includes several stages:

• preparation;
• site breakdown;
• formwork formation;
• reinforcement;
• pouring concrete.

Preparation

It consists of developing documentation, calculating estimates, precise planning and clearing the territory. In order to ultimately receive a complete package of documents, it is best to contact specialists working in the relevant field. This will save time and money, as well as professionally approach the construction of the house, taking into account the type of recommended foundation. This is especially true when constructing rear structures on soils with surface moisture.

In addition, the basis for the foundation requires a balanced approach and clarification of all details. Ideal surface evenness is also important. To do this, the area is first cleared of shrubs and other vegetation, stumps and roots are removed, and large stones and boulders are collected. Next, level it with a shovel and level, removing protrusions and indentations.

Site breakdown

This stage consists of transferring the plan to the area. To do this, a geodetic breakdown is carried out and key marks of the future building are set. Next, the entire top layer of soil is removed. It has a low load-bearing capacity and a high tendency to compaction. That is why it is removed to a depth of up to half a meter. The work is carried out using an excavator.

To backfill the pit, a gravel-sand or crushed stone-sand mixture is used at a rate of 60:40, respectively. It is compacted tightly. This pillow:

• makes it possible to reduce the force of frost heaving on the lower zone of the foundation;
• allows ground moisture to pass freely under the house;
• evenly distributes the pressure of the building on the ground.

In addition, the sandy base does not retain water, and the low-set structure does not allow the soil to freeze during cold periods, providing the structure with increased stability. Then trenches are laid across the foundation (for reservoir drainage) and lined with geotextiles. Crushed stone is poured on top of it.

Formation of formwork and reinforcement

At the corners of the resulting “structure”, rotary sealed wells are installed, since the slab foundations lie mainly on soils with a high moisture content and maximum proximity to groundwater. Then proceed to the basic formwork. According to calculations, it should extend beyond the perimeter of the foundation by 15 centimeters.

The bottom of the pit is covered with granite crushed stone of a fraction of 4-6 cm. The maximum layer thickness can reach 20 cm. A small 4-centimeter layer of concrete is formed on top of it, which is the first screed. But before this, the crushed stone is poured with a liquid mixture of sand and concrete so that the outer layer forms an even “crust”.

Next we move on to waterproofing. These can be special roll materials with adhesions or a regular bitumen primer that is used to cover cement. Any rolled waterproofing material is glued onto it. A layer of fused waterproofing is laid on top of the mastic in 2 layers. If desired, you can also make thermal insulation layers.

Then they begin to form the formwork for a monolithic reinforced concrete slab. To do this, racks are dug in around the entire perimeter of the structure and any plank materials are nailed to them. During this operation, a level is required.

The base of the foundation slab is a special metal frame with reinforcement over the entire area. For these purposes, two iron meshes are used - lower and upper. They are tied together with special hooks and annealed steel wire.

Then, additional ones are installed between the main mesh rods, at a distance of 20 cm from each other. Plastic compensators or clamps are also installed, ensuring the best location of the steel rods.

Pouring concrete

Pouring concrete is the final stage of work on a slab foundation. During its implementation, both ready-made dry mixtures and self-mixed solutions can be used - based on cement, sand and gravel (crushed stone). They fill the formwork strictly to the height of the sides. After drying, the slabs begin the next stage of construction.

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Do-it-yourself slab foundation - design, photo, video

To build a small house, you can choose the simplest foundation design - a solid slab. These foundations are a type of shallow, or rather, non-buried foundations. Their depth ranges from 40 cm to 50 cm.

Unlike non-buried columnar and strip foundations, they have rigid spatial reinforcement along the entire load-bearing plane.

Thanks to this, alternating loads that appear during uneven movement of soils are absorbed by the foundation without the occurrence of internal deformations.

Those foundations that simultaneously with the soil exhibit seasonal movements are called floating. The design of such foundations is a lattice or solid slab made of reinforced concrete cross-prefabricated beams, monolithic reinforced concrete or prefabricated slabs, the covering of which is monolithic.

Construction of a slab foundation

The construction of a slab foundation involves significant consumption of concrete and reinforcement. Such a foundation is advisable in the case of constructing a compact house or other structure where the construction of a high base is not required and the slab itself is intended to be used as a floor.

If we are talking about building a cottage of a higher class, then foundations are usually built in the form of cross-reinforced strips or ribbed slabs.

Arrangement of supporting structures

Thanks to the large support area of ​​the slabs, the pressure on the ground is reduced to 0.1 kg/cm2. In this case, cross stiffeners form a structure that is quite resistant to those alternating loads that arise when:

• drawdown,
• freezing,
• soil thawing.

The construction of such structures requires the use of high-strength concrete (class not lower than B12.5) and reinforcing bars with a diameter of at least 12 mm - 16 mm.

The relatively large volume of consumption of concrete and reinforcing steel is fully justified if all other technical solutions for foundations in these conditions cannot confidently guarantee their reliable functioning. In those buildings where the floor is located quite low above the ground level, slab foundations are even more economical than columnar foundations, since there is no need to install a grillage or basement floor.

Unburied solid slab

An unburied solid slab as an element of the spatial system “slab-above-foundation structure” allows for the perception of possible soil deformations and external force influences. In this case, it is not necessary to carry out various measures to prevent uneven soil deformations (and in conditions of sandy, heaving and weak soils, significant resources are spent on such measures).

Compared to buried structures, the use of a non-buried foundation slab can reduce labor costs by 40%, concrete consumption by 30%, and the cost of the underground part by 50%. However, in order to protect such slabs from freezing, they must be insulated.

Shallow foundation

In cold regions where there is seasonal freezing of the soil and the possibility of frost heaving, a practical alternative to the more expensive deep foundation is a frost-resistant shallow foundation.

The shallow laying of such foundations is achieved thanks to the installation of thermal insulation placed in the most important places (around the house). As a result, it becomes possible to build foundations with a laying depth of 40 cm - 50 cm (and even in very harsh climates).

Frost-resistant foundation technology

The technology of frost-resistant shallow foundations is very popular in Scandinavian countries. Such foundations are made in the form of a reinforced concrete monolithic slab 20 cm - 25 cm thick, which has thickened edges, which are contour ribs.

To protect against frost, foam insulation (foam plastic) is used.

The heat that goes through the foundation slab into the ground from the house, plus geothermal heat, causes the freezing line to rise up along the perimeter of the frost-resistant foundation.

Video. Monolithic slab foundation - cushion and formwork

Video. Instructions for constructing a slab foundation using Planter membranes

Articles about the foundation

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Foundation, installation of foundations for low-rise construction

Foundations are the supporting part of the building and are designed to transfer the load from the structures above to the base. The foundations of the building must meet the following basic requirements:

have sufficient strength and resistance to tipping and sliding in the plane of the sole;

resist the influence of atmospheric factors (frost resistance), as well as the influence of ground and aggressive waters;

correspond in durability to the service life of the building;

be economical and industrial in production.

By design, foundations are divided into: solid, strip, columnar and pile.

Bored piles: quickly and reliably, economically

What else attracts builders to such technology as bored piles? As a rule, during the traditional construction of foundations, large-scale excavation work is carried out, and special equipment is used - multi-ton piledrivers, powerful excavators, which create noise and rumble. With the bored pile method there are no such inconveniences now. Work with bored piles can be carried out in densely built-up areas, as well as on an asphalt site. At the same time, the peace of residents of the surrounding houses is not disturbed, and underground communications are not damaged. Therefore, a pile foundation created using this technology has obvious advantages.

Work with bored piles is carried out in a short time. The environmental friendliness, high efficiency and serious cost-effectiveness of this method are especially obvious with large-scale volumes of work. Therefore, the method of working with bored piles meets current construction standards. Such a pile foundation can be used in a wide range of soils, including swampy ones.

Strip foundations

In most cases, to transfer pressure to the foundation that does not exceed the standard pressure on the ground, it is necessary to expand the base of the foundation. The theoretical cross-sectional shape of a foundation with an expanded base is a trapezoid. The expansion of the base should not be too large to avoid the appearance of tensile and shear stresses in the protruding parts of the foundation and the appearance of cracks in them.

Prefabricated strip foundation made of concrete blocks for the walls of a house with a basement and technical underground:

I- foundation slab; 2 - concrete wall blocks; 3 - painting with hot bitumen; 4 - cement-sand mortar; 5 - blind area; b - two layers of idigidronzol roofing felt on bitumen mastic; 7 - basement floor

Solid foundations

They are a solid block-free or ribbed reinforced concrete slab under the entire area of ​​the building. Solid foundations are installed in cases where the load transferred to the foundation is significant and the base soil is weak. This design is especially appropriate when it is necessary to protect the basement from the penetration of groundwater at high levels , if the basement floor is subjected to high hydrostatic pressure from below.

Monolithic reinforced slab: installed on water-saturated and weak-bearing soils. Suitable for timber, log and frame wooden buildings. Completion period: 5 days.

Monolithic reinforced blind area: applicable for all types of strip foundations. Execution time: 2 days.

Columnar foundations

They take the form of separate supports placed under walls, pillars or columns. With insignificant loads on the foundation, when the pressure on the ground is less than the normative one, it is advisable to replace continuous strip foundations under the walls of low-rise buildings with columnar ones. Foundation pillars made of concrete or reinforced concrete are covered with reinforced concrete foundation beams on which the wall is erected. To eliminate the possibility of the foundation beam bulging due to swelling of the soil located underneath, a sand or slag cushion 0.5 m thick is placed under it. The distance between the axes of the foundation pillars is taken to be 2.5-3 m. The pillars must be placed at the corners of the building, at the intersection points and junctions of walls and under piers.

Columnar foundations for walls are also erected in high-rise buildings with a significant foundation depth - 4-5 m, when installing a continuous strip foundation is unprofitable due to its large volume and, therefore, greater consumption of materials. The pillars are covered with prefabricated reinforced concrete beams, on which the walls are erected. Columnar single foundations are also used for individual building supports. A more economical option is to lay reinforced concrete block slabs under the brick pillars. Prefabricated foundations for reinforced concrete columns of frame buildings can consist of one glass-type reinforced concrete shoe or a reinforced concrete glass block and a base slab under it. Columnar foundations are used mainly in the construction of industrial buildings and structures.

Prefabricated foundations for individual supports: a - for brick pillars made from strip foundation blocks; b - the same, from special reinforced concrete slabs; c - under a reinforced concrete column from a glass-type shoe; g - the same, from a glass block and a base plate

Pile foundations

They consist of individual piles united on top by a concrete or reinforced concrete slab or beam called a grillage. Pile foundations are used in cases where it is necessary to transfer significant loads to weak soil.

Piles are differentiated by material, method of manufacture and immersion in the ground, and the nature of work in the ground. According to the material, piles can be wooden, concrete, reinforced concrete, steel and combined. According to the method of manufacturing and immersion into the ground, piles can be driven, immersed in the ground in finished form, and driven, manufactured directly in the ground. Depending on the nature of the work in the ground, two types of piles are distinguished: rack piles and hanging piles. Rack piles rest with their ends on solid soil, for example, rock, and transfer the load to it (Fig. 7). They are used when the depth of solid soil does not exceed the possible length of the pile. Pile foundations on rack piles provide virtually no settlement.

If strong soil is located at a significant depth, hanging piles are used, the bearing capacity of which is determined by the sum of the resistance of friction forces on the side surface and the soil under the tip of the pile.

Types of piles in the ground:

a - hanging piles; b- rack piles: 1 - dense limestone; 2 - plastic silty loam; 3 -or; 4 - silty sand; 5 - peat; 6 - plant layer

Wooden piles are cheap, but because they rot quickly if placed in soil with variable moisture content, the heads of the wood piles should be located below the lowest water table. However, in areas with high groundwater levels, wooden piles last a very long time if they are constantly in water. In world practice, there are examples of four-hundred-year-old buildings on wooden stilts that are still in good technical condition.

Reinforced concrete piles are durable, more expensive than wooden ones, but can withstand significant loads. The scope of their application has been significantly expanded due to the fact that the design elevation of the heads of reinforced concrete piles does not depend on the groundwater level. The distance between the axes of the piles is determined by calculation. Within the most common immersion depths of piles - from 5 to 20 m, these distances for ordinary pile diameters range from 3...8d, where d is the diameter of the pile.

Driven foundation pile: 3 - reinforced concrete grillage beam; 4 - driven pile of rectangular section; 5 - dense soil

Cast-in-place suspended pile foundation: 1 - waterproofing; 2 - reinforced concrete grillage beam; 3 - cast-in-place pile; 4 - casing pipe tip; 5-weak soils I - waterproofing; 2 - surface of the earth; 3 - reinforced concrete grillage beam; 4 - driven pile of rectangular section; 5 - dense soil

Pile foundations, compared to block foundations, give less settlement, thereby reducing the likelihood of uneven soil deformations. When preparing the foundation, sometimes old filled-in wells, holes, and random weak layers of soil are found in the soil. To avoid uneven settlement of foundations, these places must be cleared and filled with masonry, lean concrete or compacted sand, and when building foundations above these places, reinforced seams should be applied.

Foundations are moistened by atmospheric moisture or groundwater seeping through the soil. Due to capillarity, moisture rises through the foundation and dampness appears in the walls of the first floor. To block the penetration of moisture into the walls, an insulating layer is placed in their lower part, most often from two layers of bitumen roll materials (roofing felt, etc.), glued together with waterproof bitumen mastic. During the operation of foundations, it is necessary to monitor the settlement of the foundation and possible deformations.

One of the important conditions for the safety and integrity of the house is waterproofing the basement. The walls and floors of basements, regardless of the location of groundwater, must be isolated from surface water seeping through the ground, as well as from capillary ground moisture rising upward. In basements, when the groundwater level is located below the basement floor, sufficient waterproofing of the floor is its concrete preparation and a waterproof floor made on it, and waterproofing of the walls is covering the surface in contact with the ground with two layers of hot bitumen. If the groundwater level is higher than the basement floor, in this case, the greater the difference in the levels of the floor and groundwater, the greater the water pressure created. In this regard, to waterproof the walls and floor of the basement, it is necessary to create a shell that can resist the effects of hydrostatic pressure.

An effective measure to combat the penetration of groundwater into the basement is the installation of drainage. The essence of the drainage device is as follows. Around the building, at a distance of 2-3 m from the foundation, ditches are arranged with a slope of 0.002-0.006 towards the prefabricated drainage ditch. Tubes (concrete* ceramic or others) are laid along the bottom of the ditches with a slope. There are holes in the walls of the tubes through which water penetrates. Ditches with pipes are covered with a layer of coarse gravel, then with a layer of coarse sand and then open soil on top. Through pipes laid in ditches, water flows into the lowlands (ditch, ravine, river, etc.). As a result of drainage, the groundwater level decreases.

When the groundwater level is located no higher than 0.2 m from the basement floor, waterproofing of the floor and walls of the basement is arranged as follows. After coating the walls with bitumen, a clay castle is made, that is, before filling the trench, crumpled fat clay is driven close to the outer wall of the basement. The concrete floor preparation is also laid over a layer of crumpled fatty clay. When the height of the groundwater level is from 0.2 to 0.5 m, adhesive waterproofing is used from two layers of roofing material on bitumen mastic (Fig. 12). The insulation is laid over a concrete floor preparation, the surface of which is leveled with a layer of cement mortar or asphalt.

Since the floor structure must withstand a fairly large hydrostatic pressure from below, a load layer of concrete is laid on top of the insulation, which balances the water pressure with its weight. On the outer side of the walls, insulation is glued with bitumen mastic and protected with a masonry of iron ore bricks of 1/2 brick with cement mortar and a layer of crumpled fatty clay 250 mm thick. The adhesive insulation of the external walls of the basement is placed 0.5 m above the groundwater level, taking into account its possible fluctuations.

1 - layer of load concrete; 2 - concrete preparation; 3 - roll waterproofing; 4 - crumpled fatty clay 250 mm; 5 - brickwork made of iron ore with cement mortar 120 mm; 6 - double layer of bitumen

Waterproofing a strip foundation in a building with a basement:

1 - concrete preparation; 2-reinforced concrete slab; 3-roll waterproofing; 4 - crumpled fatty clay 250 mm; 5 - brickwork made of iron ore with cement mortar 120 mm; b - double layer of bitumen

If the groundwater level is located more than 0.5 m above the basement floor, then a reinforced concrete slab is placed on top of the floor waterproofing, made of three layers of roofing felt or waterproofing material. The slab is embedded in the basement wall, which, working in bending, absorbs the hydrostatic pressure of groundwater.

When the groundwater level is high, installing external waterproofing sometimes causes difficulties. In such cases, it is performed along the inner surface of the basement walls. The hydrostatic pressure is absorbed by a special reinforced concrete structure - a caisson.

When laying foundations of any type, the following rules must be observed

Most foundation structures use concrete. Concrete has the property of “maturing”, 28 - 30 days. After laying the concrete structure, it must be kept for a given time without loads and it is advisable to cover it with either roofing felt or other available material to prevent the top layer from drying out. While the concrete is setting, periodically water the foundation with water to prevent it from drying unevenly. So, building a house on a newly built foundation is fraught with danger; defects will not keep you waiting.

Waterproofing your foundation is important. It consists of coating the entire surface in contact with the ground with hot bitumen. The walls are also insulated. To do this, lay two layers of roofing felt (1st layer - between the base and the zero level; 2nd layer - between the base and the main wall of the house). This protects the walls of the house and the basement from dampness.

Protection of the outer side of the plinth from atmospheric influences. This is achieved by plastering or tiling. To grout the foundation, rubber-containing components (ash from burnt car tires) are added to the mixture. It turns out to be a “fur coat” for the base. She is beautiful and reliable.

When constructing the base, ventilation openings are provided. In summer they serve to ventilate the underground, and in winter they are closed to prevent dampness from entering the house.