Concrete base for the foundation. Guidelines for the construction of foundations on a natural basis in the construction of residential buildings with a high number of storeys

Ehhhh ... Once again I appeal to the entire geodetic community: LEARN THE MATCH! In SNiPs and GOSTs, everything is described in great detail (albeit clumsily in places).

Gold words! No

Shouldn't even be near!

Now in more detail ...

SP 45.13330.2012 "Earthworks, foundations and foundations".

1. We begin to study carefully with section 6.1 "Vertical layout, excavation"(This is what they called the foundation pit here.) The most important thing here is table 6.3. Items 1 and 5 (by the way, it will be useful to remember item 9 for landscaping).
This table determines the first 2 tolerances:
- soil surface after excavation by an excavator. Most often it is + 10cm, because digging will be expensive, since you will have to do backfilling and additional compaction of the bottom.
- the surface of the bottom of the pit after the final revision is ± 5 cm.
2. Proceed to section 17.1 "Soil compaction, installation of soil cushions". Here everything is clumsy ... However, if you read carefully, then:
- Clause 17.1.1 d) allows us to get the definition: crushed stone is soil material that is rammed into the bottom of the pit when installing a soil cushion. And at the same time it gives an understanding that "crushed stone" is a kind of construction jargon not defined by the Building Rules.
- paragraph 17.1.5 "Installation of ground cushions ..." - here lies the key point in subsection a): "the ground for the installation of ground cushions must CONDENSE... ". According to the laws of physics, with the simultaneous addition of volumes and an increase in the density of the original volume (we add crushed stone to the un-rammed soil), the total volume will not change, which means that the elevation determined earlier will not change.
3. The correctness of all conclusions made earlier is confirmed by Appendix H (reference), Table H.1, p. 4 b): "The depth of the rammed pit - the deviation from the design mark should not exceed ± 5 cm."

The concept of "sand cushion" does not exist, and as a "construction" it cannot be accepted ... (there is the concept of "sand and gravel mixture", has the same definition as "crushed stone")

Further accuracy is determined from the logic of the entire pie:

1. A leveling sand-cement screed is placed on an arranged soil pad (± 5cm). From this moment on, a gradual increase in accuracy begins. Usually in the project the thickness of the screed is 5 cm. Ideally, where the soil is understated by 5 cm, the thickness of the screed will be 10 cm, and where it is overestimated, the thickness of the screed will be 0 cm. The average spread of such deviations will give an overexpenditure close to zero. The screed does not bear any bearing capacity - therefore, the actual thickness in a particular place does not matter. An executive geodetic diagram for a screed is not needed, because it is not regulated by governing documents. Precision must be ensured by foremen on the basis of beacons made by the geodesist (1 by 10-50 meters, as agreed or registered in the PPGR). The only thing that the surveyor must do at this stage is to ensure operational control, Appendix A, clause A.1 of the same joint venture about earthworks.
2. All kinds of waterproofing, etc. are laid. - they are not of interest to us, since they have a specific thickness, and the foremen and the maintenance department will calculate the areas themselves.
3. The concrete base of the foundation slab is poured (it is also "footing") and only here we start talking about sane accuracy and apply the joint venture "Bearing and Fencing Structures". In fact, the thickness of the slab depends on the correct filling of the foundation. And the executive is needed not so that the greedy director calculates the overrun, but so that if any jambs come out after pouring the FP, it would be possible to estimate the thickness of the poured slab and the designer's supervision could decide on the preservation of the bearing capacity and on the conditions for further construction. Naturally, logic says that the tolerances of SNiP "Bearing and Fencing Structures" already apply to the foundation.

They say that chickens are milked

Click to Expand ...

Thank you for your enlightenment in this area, alas, at one time they explained to me differently, learn to live!

Before proceeding with the construction of the foundation, it is necessary to take care of the proper preparation of the construction site. It is needed in order to prevent the leakage of cement laitance during the pouring of the slab or tape. This will allow you to get a high-quality and durable base for your home.

Preparation device

Stages of work:

• the construction site is marked for the construction of the foundation;
• the site is leveled;
• crushed stone is poured with a layer not thicker than 10 cm;
• the pillow is compacted using a vibrating plate;
• formwork is mounted along the perimeter, verified using the markings;
• the height of the formwork must correspond to the thickness of the concrete layer. In most cases, it does not exceed 30 cm. The concrete is poured flush with the top of the formwork;
• to give the pillow strength, it is recommended to strengthen it with reinforcement. For these purposes, use reinforcement with a cross section of 8 mm;
• during pouring, concrete should be tamped using a vibrating plate;
• the size of the site on which the concrete preparation is carried out may exceed the size of the foundation slab or tape by 10-15 cm on all sides;
• after pouring into concrete, it is recommended to vertically install reinforcing bars, which will tie the pillow to the foundation. They should protrude 20-30 cm above the concrete surface;
• a concrete base is considered the most reliable today and is recommended for all types of foundations and buildings.

The concrete base can be reinforced, or reinforcement can be dispensed with. For practical use, both of these grounds are almost equivalent. The only difference is that the unreinforced pillow has size limitations. According to building codes, the minimum thickness of the concrete layer in this case must be at least 15 cm. reinforcing mesh, which is laid at the bottom of the pit in such a way that it is at a distance of 5 cm from the ground.

This will allow the mesh to be positioned in the most optimal way. It can be made from reinforcement bars with a thickness of at least 8 mm, tied together with a knitting wire. The mesh can also be welded. It will reinforce the bottom of the concrete pad, which is subject to tensile forces from the weight load of the building transmitted through the foundation.

Pros of a concrete base

This type of foundation tape is good because it allows you to take long breaks in work, which is impossible when installing a filler strip base... For its construction, you can use both home-made concrete blocks and factory-made ones. V recent times blocks of expanded polystyrene are becoming more and more popular. They are significantly lighter in weight and do not require as careful site preparation before installation.

For heavy building stones, it is recommended to arrange a crushed stone base with a pouring of it with lean concrete or bitumen. The thickness of the layer depends on the expected weight loads of the building and the type of soil. Where it is denser, less thickness is needed concrete preparation... For heaving soils, the thickness of concrete and crushed stone must be at least 15 cm.The thickness of the protective cement layer over crushed stone is at least 3 cm.

For blocks of foam concrete and aerated concrete, you can arrange a concrete base not on crushed stone or gravel, but on sand. For this, sand is poured to a thickness of at least 10 cm. The sand is spilled and compacted. Then the formwork is mounted to the height of the concrete layer and the grout is poured. The recommended thickness is from 5 cm. Concrete preparation for the foundation is always more preferable than a compacted sand cushion.

Laying a high-quality foundation is the key to the durability and strength of any building. This will require not only good building materials, but also knowledge of construction technology. And one of the fundamental points of this technology is the arrangement of a special preparatory site. In the case of tape and monolithic base it is absolutely necessary, and in this article we will tell you in detail how to make concrete preparation for the foundation.

Concrete foundation preparation is necessary to level the base before pouring the tapes or slabs. In addition, it does not allow the laitance to be absorbed into the soil. If this happens, and the liquid leaves the concrete solution, the foundation, after solidification, will turn out to be fragile and unable to cope with its purpose. Before starting construction, you should make calculations and start preparing the construction site. The preparation itself can be made of concrete, bulk or film materials, but in any case, it must meet certain technical requirements. According to SNiP, concrete preparation for the foundation is characterized by a regulated thickness, depending on the selected material. You can get acquainted with the basic norms in SNiP 52-01, SP 52-101 for 2003 and in SP 50-101 for 2004. In general terms, the creation of a preparatory site for the foundation gives the following results: Protection of the concrete layer from leaks, which will allow the foundation to quickly gain the required volume and improve performance. Leveling of force effects provoked by ground movements. In other words, concrete preparation evenly distributes the load over its entire area and at the same time weakens the heaving forces of the soil, preventing them from harming the house. Providing comfortable conditions for laying the reinforcement cage - it is much more convenient and faster to work on a flat surface. So, concrete preparation for the foundation can be created from lean concrete, gravel or profile membranes. Let's consider the use of these materials in more detail. Concrete platform Since the main task of the concrete site for the foundation is to exclude the possibility of soil shrinkage from a large load, the use of a lean concrete solution is quite justified. It will provide the base with good stability, create a solid and even surface for work. On the other hand, the use of lean concrete is not always financially rational, but, despite this, this method is the most popular. Lean concrete is a mixture in which the content of the cement part does not exceed 6%. Moreover, for mixing, they take low-grade cement (M100). Crushed stone or gravel are used as fillers to increase strength. The bottom of the dug pit is poured with a solution of lean concrete, and after it has solidified, they begin to install the reinforcement and pour the foundation. The thickness of the concrete preparation for the foundation may vary depending on the characteristics of the soil, the load on the foundation, the level of groundwater, the area of ​​the future structure, etc. These provisions are spelled out in detail in SNiP. The recommended thickness is 40-100 mm. Concreting the foundation pit eliminates the risk of deformation of the reinforcing cage, as well as the walls of the foundation slab (tape). If you have to do work in cold weather, antifreeze additives should be added to the lean concrete mortar. Helpful advice: In winter, it is easier to make concrete preparation than crushed stone, since it is almost impossible to work with frozen crushed stone. Crushed stone preparation Crushed stone or gravel preparation is a good alternative, however, it is relevant only in the case of arranging support-pile grillages or monolithic foundations... Backfill thickness can vary from 100 to 200 mm depending on soil characteristics, load and other factors. Often, builders use a mixed technique, filling the bottom of the pit with gravel, and then pouring it with lean concrete with a layer of up to 80 mm. Such measures are especially relevant if the construction of the foundation will be carried out with heavy materials: stones, rubble concrete blocks, etc. If the site is located on heaving soil, the thickness of the crushed stone layer should be at least 150 mm, and the thickness of the concrete fill should be at least 30 mm. For relatively light materials, for example, aerated or foam concrete blocks, preparation can be made from sand. To do this, it is poured with a layer of 10-15 cm, tamped, assembled the formwork and poured the foundation. Building codes do not provide a clear answer to what kind of preparation is needed in each case. It is only known that for crushed stone preparation, a bulk layer thickness of no more than 200 mm is sufficient. If the foundation of the future home is monolithic slab or any other similar type of base, reinforced frame structures, it is better to do concrete preparation. Among other things, it should be borne in mind that crushed stone preparation implies subsequent pouring with molten bitumen, which evens and hardens the surface, and also creates a reliable waterproofing layer. It is clear that in winter, to create such a pillow will require more resources to warm up, so it is better to work with rubble in the warm season. Preparation from profile membranes Manufacturers of profile membranes for working with foundations all as one claim that their products can fully replace any crushed stone or even concrete preparation. In some cases, this is the case. The advantage of using membranes is the efficiency and cleanliness of the work - no fiddling with the solution or bulk materials... It is enough to lay the membrane on the bottom of the pit and start laying the foundation. How to make concrete preparation Despite the possibility of choice, many people prefer to rely on traditions and make concrete preparation for the foundation. The price of such an event may be higher, but the result allows you not to doubt the durability of the building. In a lean foundation, the concentration of cement is very low. It is used not only for arranging foundation preparation, but also for pouring floors. To prepare the solution, you will need B15 grade cement, while for all others construction works it doesn’t work - it’s too fragile. 1 bag of cement will require about 344 kg of sifted river sand and 10-11 liters cold water... We recommend reading about how to choose the right sand in the article. Sequence of work: Experts recommend making concrete preparation under strip foundation with a small margin in all directions - literally 10-15 cm. This will strengthen the stability of the foundation and remove excess moisture from it. This pouring technology can be used for any kind of foundation, but when it comes to building from lightweight materials, you can save on materials and make a lightweight version (sand cushion). Important: If you decide not to reinforce the foundation cushion, the concrete layer should rise 15-20 cm above ground level. The device for concrete preparation for the foundation is quite simple, but this does not mean that you can do without it. If the tapes or base slab is installed directly into the ground, it will lead to inevitable and very early destruction of the house. On the other hand, preparation from crushed stone and concrete extends the service life for many years.

The stability of foundations depends on the quality of the foundation preparation. Its choice and arrangement is largely determined by the material of the underground structures and the soil conditions of the building site. Concrete preparation for the foundation is considered the most reliable and expensive in comparison with sand and crushed stone cushions. Most often, it is performed under monolithic tapes and plates, taking into account the requirements of the relevant SNiP and SP.

What is the foundation for?

First of all, the preparation of the site for the foundation is aimed at strengthening and leveling the base. But the concrete layer is also a barrier that protects the future underground monolith from the loss of cement laitance, which, when concreting the structure, can simply seep into the ground or the underlying layers of rubble and sand. The concrete helps to retain moisture in the mortar mass, which is required for the correct passage of the concrete curing process. If there is not enough water, the cement will not be able to fully reveal its properties, and this will lead to:

• to the appearance of cracks in the concreted structure;
• to a shortage of design strength;
• to further destruction of the foundation during the period of operation.

The device at the base of the underground part of the house of a concrete site in accordance with SNiP contributes to the most uniform distribution of loads acting from the soil and the above-ground part of the structure. Preparation for a concrete foundation allows you to level the bottom of the excavation and position it stably in the formwork reinforcement cage for monolithic tape or slab. In addition, the underlying layer virtually eliminates the occurrence of soil shrinkage due to the impact of large or point loads.

Another reason that determines what a foundation is for is that, on a hard and even layer of preparation, the construction of a foundation in winter is easier.

Normative documents - SNiP and Code of Rules (SP)

The device of any structures during the construction of civil and industrial facilities obeys certain requirements specified in the relevant SNiP and other standards of state and industry significance. Concrete preparation for the foundation is carried out based on:

• SNiP 2.02.01-83;
• SP 63.13330.2012;
• SP 50-101-2004.

These documents define measures for the design and construction of foundations, taking into account:

• type of soil;
• surrounding buildings;
• acting loads;
• seismicity;
• environmental requirements.

The thickness and width of the concrete preparation for the foundation is calculated according to SNiP, according to the bearing capacity and possible deformations. In the first case, the calculation is required if:

• the presence of significant compressive loads is assumed;
• the structure is supposed to be located near slopes, on a slope or embankment;
• there are soft soils under the foot of the foundation.

It should be noted that SNiP allows not to make calculations for the bearing capacity, if the project provides for measures that exclude soil displacement for the previously mentioned reasons.

All long and short-term forces transmitted from the structure, including the weight of the underground part of the structure, are taken as loads on the concrete preparation of the foundation. Possible combinations are indicated in SNiP.

Foundation device

Regardless of the type of soil, at the first stage of work on the preparation of lean concrete for the foundation, the bottom of the excavation should be leveled. For your information, for a monolithic tape it will be enough to dig a trench, and a foundation pit is required for the slab. When determining the excavation depth, the thickness of the foundation and the thickness of the sand and gravel layer, laid directly on the ground, are taken into account.

Loose soil must be tamped, and sand and crushed stone must be added to the bottom of the excavation. The layers are also compacted. Crushed stone, in this case, will perform a drainage function. Further, roofing material or films are laid on the surface as waterproofing.

Concrete preparation for monolithic tape or foundation slab should protrude along the perimeter beyond the underground structure by 10-15 cm. With this in mind, a crushed stone-sand base is made and a formwork device for pouring the base is performed. The height of the box is taken based on the thickness of the preparation for the foundation.

In the next step, a lean concrete mortar is mixed, which contains a small volume of cement. Gravel and sand are used as fillers. After the concrete is poured into the formwork, it will need to be tamped to get rid of air bubbles and leveled. In the first few days, the surface of the concrete preparation is covered with plastic wrap to prevent excessive drying of the surface.

It is important to know that the base for the foundation, which is not reinforced with reinforcement, has size restrictions.

Reinforcement significantly strengthens the foundation and increases the reliability of the underground part of the structure. The nets are knitted by means of wire from rods with a diameter of eight millimeters, and laid before pouring the solution. To ensure reliable conjugation of the concrete preparation with the foundation, metal rods are vertically installed in the base thickness so that they protrude 20-30 cm above the concrete surface.

The optimal thickness of the concrete without reinforcement is 15-20 cm. When installing a reinforced concrete base for a foundation, the size of the preparation can be reduced to 6-10 cm. The SNiP indicates the maximum deviation of the horizontal surface - no more than 5 mm per meter when installing a monolithic tape and no more than 50 mm for a slab more than 25 meters wide.

Concrete foundation preparation serves to:

· Evenly distribute and redirect the forces acting from inside the soil and adversely affecting the state of the foundation.

· Provide a level surface for further construction work.

· Prevent liquid part of the mortar from escaping when pouring the foundation. This contributes to the fact that the thickness of the concrete preparation for the foundation is recruited much faster and the entire foundation becomes stronger and therefore more durable.

Before starting construction work, it is necessary to carry out careful calculations, taking into account the characteristics of the soil, climate conditions and the requirements for the construction of a concrete base. The foundation can be made from concrete, as well as from loose or synthetic materials, but they must necessarily meet all standards. All requirements for the process of preparing a concrete base can be found in the SNIP.

Preparing the soil for pouring a concrete base.

· Carrying out the necessary measurements and preliminary work.

· Digging a pit.

· Leveling and compaction of the soil using a vibrating plate.

· If necessary, the soil can be moistened or drained.

Using lean concrete

Skinny concrete usually consists of a small amount of cement (4 to 7%) grade B 7.5, while the bulk of it is crushed stone or gravel. Cement grade B15 can also be used, it has increased strength characteristics and is more resistant to corrosion.

If the concrete preparation of the foundation is prepared in the cold season, various means are also added to the cement mixture to improve the resistance of concrete to negative temperatures.

The process of pouring lean concrete takes place in several stages:

· A thin layer of sand is poured. It absorbs well and evenly distributes the pressure of the building to the ground. The sandy layer prevents the negative impact of groundwater.

· A cement solution is poured into the bottom of the pit with a thin layer, after which it must be leveled. The thickness of the concrete preparation for the foundation should be about 100 mm.

· Everything is carefully covered with polyethylene to prevent drying out.

Filling stages. Concrete preparation device for the foundation

1. The construction site is thoroughly cleaned of debris. The top ball of soil with grass and roots is removed (up to 30 cm).

2. Marking the site for construction using pegs and a stretched thread. The pegs are installed in 50 cm increments and must be installed at the corners.

3. The soil is leveled and moistened / drained. Then a thin layer of sand is poured out and leveled.

4. Crushed stone or gravel is filled in and leveled with a layer of 60 to 100 mm.

5. With the help of a vibrating plate, everything is carefully compacted.

6. Formwork is being prepared from wood panels paved inside with parchment. This is done to make it easier to dismantle the formwork later.

7. Concrete preparation of the foundation is poured. The upper level of the mortar must coincide with the height of the formwork.

8. If necessary, mount the frame reinforcement. This requires corrugated rods up to 8 mm thick.

9. The concrete is compacted with a vibrating plate.

10. Reinforcing vertical metal rods are installed, fastening the foundation with the preparatory pad. They should be 30-40 cm higher than the thickness of the concrete preparation for the foundation.

In a situation where during work on the street hot weather with low humidity, the concrete base should be moistened with water to prevent cracking and deformation of the concrete. The next day after pouring the cement mortar, it is necessary to cover the concrete preparation with a thin layer of wet sawdust and then moisten them with water for seven days.

Being enough durable material, concrete is not plastic at all. It perfectly withstands vertical loads, but when deformed by stretching or twisting, it tends to crack or creep over the entire thickness of the concrete. In order to prevent this, reinforcement is used. Metal corrugated rods are laid in a reinforcing frame and then tied with wire or by welding.

Welding is used only for fittings marked "C".

Reinforcement reinforces, first of all, those zones of the preparatory cushion where the concrete preparation of the foundation will most likely deform: in the lower part of the concrete layer and at the corners. However, reinforcement is not mandatory and, if it has not yet been performed, the thickness of the concrete preparation for the foundation must be at least 15 cm.