Determining the size of the base of the foundation for the house. How to calculate the dimensions of the foundation Strip foundation thickness

Calculating the size of the foundation for the house is a painstaking work that requires attention, because the quality of the above-ground part of the house depends on its correctness. As a rule, there is a standard system, it was compiled by architects, it is quite simple and should not be used for houses of complex construction, as there may be some discrepancies. If you want to know how to do it right, read on….

The most basic task of each developer is to build a foundation that is durable and reliable, and in order for it to meet the requirements, they select the appropriate geometry. To make it easier to calculate, look at the finished foundations that are ideal for your architectural plan. It is worth paying attention to the shape, quality and defects. They will point out to you what mistakes were made at the time of construction.

Options

After a visual acquaintance, you can safely proceed to a full-fledged calculation, which includes the values ​​\u200b\u200bof the bearing capacity and the deformation of the soil in the area where the foundation will be built. This requires knowledge of mathematics and physics.

The calculation of the bearing capacity is not complicated, it is difficult to deform - it should be done with professionals.

Take, for example, a strip foundation. The following data will be required:

1. Soil quality.
2. Level of ground water leakage.
3. Ground freezing mark.
4. Architectural project of the house.

Having objective data, you can proceed to the phased calculation of the foundation.
The first stage is the determination of the weight of the external structure of the house, which is above the ground, including the additional load from furniture, decorative finishes, etc., which will produce a specific pressure on the sole soil.
The second stage is geometry.
The third stage is adjustment.

How to determine the size of the foundation for an economy class house?

For this type of house, it is necessary to determine:

• the specific gravity of the external structure, located above the base of the foundation, while taking into account the weight of the soil itself;
• plinth, including decorative trim, floors and floor slabs;
• wall panels, excluding door and window openings;
• partitions with external and external finishing. A similar calculation is made directly with the walls;
• truss system and ceiling, including trim and roofing material;
• flights of stairs;
• insulating layer.

You will need a drawing paper, on which you will need to sketch all the structural elements of the house. The sketch should be as similar as possible to the real design. At the end of the sketches, the volumes of the structure are determined according to the formula - LxHxW = V. If it is necessary to determine the volume of a complex structure, then it is necessary to divide the foundation into parts and calculate their volume according to the proposed formula. The result is multiplied by the weight of the construction material. As a result, the weight of the structural element will be known, it must also be determined.
To find out the weight of the material, you need to multiply the resulting weight according to preliminary calculations by the load safety factor.

The safety factor depends on the nature of the load.

At the end of the summation of the weight of all structural elements, the weight of the whole house should be obtained, in the sketch it is designated - "Rk". The dimension of the weight of the house is indicated in tons or kilograms.

1. The determination of geometric parameters is carried out taking into account the deepening of the foundation, the parameters of the house plan, material, soil classification, as well as the planned structure.
2. According to the final calculations, a diagram and a sketch are drawn up, where the width of the structure depends on the category of soil. It should be noted that the width of the soil, regardless of what soil it is arranged on, should not be less than 350 mm and less than the width of the walls of the house.
3. The height of the house depends on the amount of foundation immersion in the ground.

To determine the snow load on the roof of a house, a standard formula is used - Correction factor X per Pc, resulting in an updated snow load Pc *.

Video

We offer you to watch a video about the errors of laying the foundation:

Strip foundation height
The maximum height of the above-ground part of a monolithic strip foundation with internal filling of the space limited by the tape with soil (sand) should be equal to four dimensions of the width of the strip foundation. (Foundation height above ground = 4x foundation width)

*The table is given according to the table3.2 from the design manual "Reinforcement of elements of monolithic reinforced concrete buildings", Moscow, 2007.

For example, the total height of the underground and aboveground parts of a strip foundation 40 cm wide should have an optimal height of 80 cm to 120 cm.
According to English recommendations, the aboveground part of a monolithic shallow strip foundation cannot be larger than its underground part, but can be arbitrarily smaller than the underground part of the foundation. The most common option is the depth of laying a monolithic shallow strip foundation and its height above the ground equal to 50 cm, that is, the total height of the strip is 1 meter (if the conditions of the underlying soils allow). If you need an above-ground plinth 80 cm high, then it is recommended to arrange the underground part of the strip foundation with a depth of at least 80 cm. These English recommendations (like many others) are not confirmed by the requirements of Russian building codes, but may be useful when designing reliable strip foundations.

The length of the building on the strip foundation
Extended buildings should be cut along the entire height into separate compartments, the length of which is taken: for slightly heaving soils up to 30 m, medium heaving soils up to 25 m and strongly heaving soils up to 20 m, excessively heaving soils up to 15 m [VSN 29-85].

Strip footing width
Minimum structurally limited. the width of the foundation strip is 15 cmand not less than the width of the shoulder of the concrete cushion protruding from under the tape [ BR 2010 A1/2, paragraph 2E2-c] , and for strip foundations for country houses, the minimum width is at least 25 cm - 30 cm. The width of a strip shallow foundation cannot be less than the width of the wall supported on it. The minimum width of the strip foundation for light garden buildings (arbors, sheds, sheds, small baths) must be at least the minimum allowable width of a reinforced concrete beam, that is, 15 cm.
In addition to the minimum design restrictions, there are also requirements set by bearing capacity of soils under foundations. The specific load from the building per unit area should not exceed 70% from the bearing capacity of the soil. You can regulate the amount of load using the area of ​​\u200b\u200bsupport of the foundation on the ground. The larger the support area, the lower the specific load transferred to the ground.

For single-family (individual) frame residential buildings, which make up a fairly large proportion of all summer cottages, there are separately prescribed standards for the depth of foundations in the Code of Rules SP 31-105-2002 “Design and construction of energy-efficient single-family residential buildings with a wooden frame”. They are applicable when the following conditions are met simultaneously:
the span of floor beams resting on foundations (basement walls) does not exceed 4.9 m;
calculated uniformly distributed loads on floors do not exceed 244 kgf/m2;
design soil resistance is not less than 0.75 kgf/cm2.

Table number 20. The minimum width of the strip foundation for an individual frame house.*

How to build a solid foundation? The durability of the structure depends on the strength of the foundation. Let's discuss the options:

• foundation depth,
• foundation area (foundation base area).

The choice of the optimal foundation size is often called foundation calculation.

It is important to choose the right size of the foundation: the depth of the foundation and the area of ​​​​the base of the foundation. During the construction of the house and during the first two years, the soil under the house is compressed under the weight of the house. Foundation settlement occurs. Uneven settlement of the foundation leads to cracks in the walls and foundation, warping of the walls and destruction of the house.

The foundation may sink unevenly due to various factors, for example:

1. in winter, heaving soils swell,
2. the base of the foundation is loose soil,
3. not a horizontal base of the foundation,

For the correct calculation of the foundation, you must first study the structure of the soil on the site, the depth of soil freezing and the level of groundwater. Considering all factors, you can choose the optimal depth of the foundation.

Foundation depth and soil type

The foundation will be strong if the base is a homogeneous soil. Such soil settles evenly and the foundation will not warp or crack. also depends on the type of soil. Consider the types of soils: rocky, cartilaginous, sandy and sandy loam, clay and loam.

Rocky soil allows you to lay the foundation of the structure on the surface, removing a thin fertile layer of soil.

Cartilaginous soil consists of gravel, cartilage, large stones. The foundation on such soil is laid at a depth of at least 500 mm. The depth of the foundation is determined by the load of the structure and the level of groundwater, it does not depend on the depth of soil freezing.

Sandy soil passes water well, so water does not stagnate near the surface, even with a high occurrence of groundwater. Insignificant freezing of sandy soil and the mentioned factor allow laying the foundation to a depth of 500-700 mm. If the sandy soil is fine-grained or dusty and the groundwater is high, then such soil can freeze significantly and then the depth of the foundation increases to the depth of freezing of the soil. It should be borne in mind that sandy soil is strongly compacted under load and a heavy structure can settle heavily, so we recommend making a high base. Similar recommendations are also suitable for clay-sandy soil - sandy loam containing 3-10% clay, but the recommended foundation depth drops to 700-1000 mm.

The foundation on clay soil is laid just below the freezing depth of the soil. This is especially important at high groundwater levels. Clay soil has the ability to compress under load and swell when frozen, as if pushing the foundation to the surface. So that the foundation does not crack at the same time, we advise you to make a high-strength foundation and give preference to a columnar foundation. The foundation on loam is also laid below the freezing depth of the soil. Loam contains sand and at least 10-30% clay.

Groundwater level and foundation depth

The position of the groundwater level affects foundation depth in the following way:

If the groundwater is deep, more than 2000 mm below the freezing depth of the soil, then the foundation can be laid to a depth of 500 mm or less.

If the groundwater is not so deep, but below the depth of freezing of the soil, then either the foundation is laid to the depth of freezing of the soil, or a gravel-sand cushion is laid from the depth of freezing of the soil to the bottom of the foundation (it is well tamped), and the foundation is laid to a depth of 500 mm and below.

If the groundwater reaches the level of soil freezing, then the depth of the foundation should be lower than the freezing depth of the soil by at least 100 mm.

With a high location of groundwater, the foundation is laid below the freezing depth of the soil, with the exception of the presence of sandy soil and year-round heating of the structure.

Optimum foundation depth

Optimal foundation depth is chosen as follows. If the soil under the house is heaving, then the foundation must be laid below the freezing point of the soil, in Central Russia at a depth of 1500 mm (the depth of soil freezing is about 1200-1400 mm). To the south and west of the country, the depth of soil freezing decreases, and to the north and east it increases. In each area, through many years of observations, experts have established the depth of soil freezing, which can be found in the local construction or design organization. If they live in the house all winter, then you can ignore this factor and lay the foundation higher.

The base of the foundation should be a dense, well-packed soil, so the foundation is laid below 500 mm. A layer of loose soil is removed, the bottom is leveled horizontally, a sand cushion 150 mm high is made, which is well rammed.

The foundation for the internal main walls is laid at a depth of 500 mm.

Foundation area

Optimal foundation area is selected from the calculation so that the soil does not sag under the weight of the house. The soil sags under the weight of the house when the load on the soil is too great. The load on the ground can be reduced by increasing the base area of ​​the foundation. For a strip foundation, in order to obtain the required foundation area, increase the width of the foundation walls. For a columnar foundation - increase the number of pillars and increase their length and width, bringing up to 500 mm.

For one-story or two-story summer garden houses, the size of the foundation is usually the same, because. the bearing capacity of the soil will withstand this load. The size of the foundation depends on the thickness of the walls and the depth of soil freezing. To build a solid but economical foundation for a summer garden house, it is recommended to use a column foundation and avoid unreasonable thickening of the foundation. With unfavorable soil properties, only the lower part of the foundation can be expanded.

A strip foundation is usually erected under a building with heavy walls made of brick or reinforced concrete. With a shallow foundation, it is advisable to make a strip foundation. If the building will have a basement, a strip foundation is also built. In suburban construction, it is not recommended to make an extended strip foundation to its entire height. If necessary, only the base of the foundation is expanded: it is concreted and reinforced. The thickness of the foundation usually corresponds to the thickness of the wall of the building.

A columnar foundation is built under a frame or wooden structure with light walls. Pillars are erected at the corners of the building, at the intersection of walls and in other places where the load is concentrated. Pillars are placed at a distance of 1500-2500 mm. The distance is determined by the weight of the house and the bearing capacity of the soil. On sandy loam and sandy soils, posts are placed at a distance of 1500-2000 mm. On rocky, cartilaginous, clay soils and loam, the pillars are placed at a distance of 2000-2500 mm.

Foundation calculation

For the foundation to be reliable, the area of ​​​​the base of the foundation must satisfy the inequality:

(Foundation area, cm²) x (Soil bearing capacity, kg/cm²) > (House weight, kg)

1) Soil bearing capacity depends on the type of soil under the foundation and is determined according to table 5. The bearing capacity of the soil is called the design resistance of the soil.

2) House weight consists of the weight of the foundation, walls, roof, floors, as well as the weight of snow on the roof, people and all objects in the house, incl. furniture, bathroom and pool with water, billiards, piano.

The weight of the foundation, walls, roof, roof slabs can be calculated using tables 1-4.

The weight of snow on the roof is calculated based on the specific weight of snow cover in Central Russia 100 kg/m².

The weight of people and objects in a house for a cottage and a country house is calculated, as for a city apartment, according to the formula

400 kg/m² x (Total floor area, m²)

If a pool or other very heavy object is supposed to be in the house, its weight must be added to the weight of the house.

For a country house where there is no cast-iron bath, piano, billiards, crowds of guests, you can calculate the weight of people and objects in the house using the formula

200 kg/m² x (Total floor area, m²)

Reference tables

Table 1. Weight 1 m³ foundation

Table 2. Weight 1 m² walls

Table 3 Weight 1 m² floors

Table 4 Weight of 1 m² of roof

Table 5 Soil bearing capacity

The strip foundation is perhaps the most popular type of foundation used in low-rise construction. This is primarily due to its versatility, since it is possible to build a house on it from almost any material. Another question is that this is not always economically feasible, but more on that later. What is this type of foundation, it is clear from its name. This is a single structure in the form of a strip of a certain solid building material located under all the load-bearing walls of the building.

According to the design, monolithic and prefabricated strip foundations are distinguished. Monolithic - made of monolithic reinforced concrete, prefabricated - foundation made of FBS blocks or small-piece materials (brick, rubble stone).

According to the depth of occurrence, strip foundations are divided into deep and shallow, which were discussed separately.

In this article, it is the buried monolithic strip foundation that will be considered.

Main advantages:

• high strength and ability to withstand significant weight of the house;
• greater reliability and durability;
• the ability to build on their own;
• Possibility to build a basement (basement).

Flaws:

• significant labor costs due to the large volume of earthwork and concrete work;
• significant material costs for concrete and reinforcement;
• frankly, the dubious prospect of making a high-quality foundation without the involvement of construction equipment (we will talk about this later).

You can not choose a buried strip foundation when building on organic, loess soils, on peat bogs, on fatty water-saturated (even seasonally) clays, on fine and silty sands, which are especially susceptible to moisture.

Important: The groundwater level should ideally not rise closer than 2 meters to the base of the foundation. Otherwise, it is better to establish the possibility of choosing this type of foundation (especially when building a massive brick house) when conducting geological and geodetic surveys, because. it will be determined precisely by the composition of the soil and its homogeneity at the site. Perhaps this type of foundation will have to be abandoned or a drainage system will need to be made. Remember that for a number of soils, when moistened, the bearing capacity changes very much. This can lead to sad consequences.

The main mistakes in construction.

1. thoughtless and not justified by any calculation choice of the basic geometric parameters of the foundation tape, such as its height and width.
2. pouring concrete directly into the excavated trench, without taking measures for its waterproofing and insulation;
3. errors when reinforcing the foundation and when laying household communications in the tape;
4. other errors associated with the technology of work.

Now consider how these negative factors can be avoided.

Calculation of the strip foundation.

When calculating, it is necessary to compare the total weight of the entire house and the foundation itself with the bearing capacity of the soil. The first should be less than the second, moreover, with a certain margin. You can do this in the following sequence:

I) We examine the building site. All information on this subject is provided

Based on the data obtained, we accept the depth of the foundation by 30-50 cm more than the estimated freezing depth. At the same time, you must understand that, starting from the estimated depth, you will have to observe the chosen thermal regime in the house in the very first winter. In other words, the house must be heated. Otherwise, if the house stays cold in the winter, the standard freezing depth is taken into account.

The width of the foundation tape is initially taken equal to 20 cm. This is the minimum value, which will increase if necessary in the further calculation.

II) Determine the weight of the house, which will act on the bearing layer of soil.

The approximate specific gravity of individual structural elements of the house is given in the following table:

Also note that the snow load when the slopes are more than 60º is assumed to be zero.

III) We calculate the weight of the foundation itself. From the project of the house, we know the total length of the foundation tape. Its height and width are defined above, in paragraph I. We multiply these values, we get the volume of the tape. We multiply it by the specific gravity of reinforced concrete, equal to 2500 kg / m³, and thereby obtain the weight of the foundation.

We add this figure to the weight of the house (point II) and get the total load on the bearing soil (P, kg).

IV) Now we calculate the minimum allowable the value of the required width of the base of the foundation B (cm) according to the formula:

B \u003d 1.3 × P / (L × Ro),

where 1.3 is the safety factor of the bearing capacity;

P - the total weight of the house with the foundation (item III), kg;

L is the length of the tape (translated into centimeters), cm;

Ro is the resistance of the bearing soil, kg / cm². Its value is approximately taken from the table below:

Once again, we note that the bearing capacity values ​​in the table are given for soils of normal moisture content. When the groundwater level rises to the bearing layer, the values ​​of Ro will change greatly (for example, for oily clay it can decrease by almost 6 times, and for fine sand - by almost 4).

v) If the resulting value of the tape width turned out to be less than the 20 cm selected at the beginning, then we take the final width to be exactly 20 cm. compressive strength of the foundation will not be ensured.

If we got a width exceeding the initially selected 20 cm by more than 5 cm, then we need to repeat the calculation, starting from III point, substituting the new width when determining the mass of the foundation.

Such repeated calculations are performed until the increase in the width of the tape is less than 5 cm. For those who are a little confused, let's give a small example.

An example of a simplified calculation of a strip foundation.

Let us determine the minimum allowable width of the base of a recessed strip foundation for a 2-storey brick house (see Fig.) 10 × 8 meters in size with one load-bearing partition in the middle of the long side. The height of the walls is 5 m, the height of the gables is 1.5 m. The thickness of the walls is 380 mm (one and a half bricks), the basement and interfloor ceilings are made of hollow-core slabs, the roof is metal. The bearing soil is loam with an estimated freezing depth of 1.1 meters.

I) Based on the depth of freezing, we accept the depth of the tape with a wound of 1.6 meters. To begin with, we take the width of the tape equal to 20 cm.

II) We calculate the weight of the house:

1. The total area of ​​the walls of the house, together with the gables and with the internal load-bearing partition (also folded into one and a half bricks), minus the window and door openings, in our case will be 212 m², and their mass is 212 × 200 × 3 = 127,200 kg.

2. The total area of ​​the basement and interfloor floors is 160 m², and their weight, taking into account the operational load, is 160 × (350 + 210) = 89,600 kg.

3. The roof in our example has an area of ​​about 185 m². Its mass with a metal roof and snow load for central Russia will be 185 × (30 + 100) = 24,050 kg.

4. We sum up the figures obtained and get 240,850 kg.

III) The weight of the foundation itself, 1.6 m high, with a total tape length of 44 m and with a previously accepted width of 0.2 m, will be 1.6 × 44 × 0.2 × 2500 = 35,200 kg.

The total weight of the house will be 276,050 kg.

IV) Taking the Ro value for loam equal to 3.5 kg / cm² and converting the total length of the foundation tape into centimeters, we calculate the desired width:

H \u003d 1.3 × 276 050 / (4400 × 3.5) \u003d 23.3 cm

v) We see that the obtained value does not exceed the initially accepted 20 cm by more than 5 cm. Therefore, the calculation can be completed on this and the minimum possible width of the base of the foundation can be rounded up to be 24 cm.

Conclusion: having made the width of the base of the foundation more than 24 cm, we can expect that this soil will withstand the house in terms of its bearing capacity.

Now, in a nutshell, what would happen if the bearing capacity of the soil was, for example, 2 kg / cm². Then the width of the tape would be 40.8 cm. After that, we return to point III. The mass of the tape becomes already equal to 71,800 kg, therefore the total weight of the house is 312,650 kg, and the specified width of the tape B = 1.3 × 312,650 / (4400 × 2) = 46.2 cm.

We see that the discrepancy with the previous value of 40.8 cm was again more than 5 cm, so we return to point III, we consider the mass of the foundation, the whole house and an even more refined width of the foundation tape. By the way, this time it will turn out to be equal to 47.6 cm. The discrepancy with the previous value is only 1.4 cm, so the calculation can be stopped and the minimum possible width of the foundation sole is 48 cm.

Please note that 48 cm is exactly the width of the sole, and not the entire tape. It can be narrowed, up to 20 cm (depending on the thickness of the wall and the structure of the ceilings), and at the bottom only an extension is made (see the pictures below). By the same principle, heavily loaded prefabricated foundations are made from FBS blocks. First, wide foundation pillows are laid, and already narrower foundation blocks are placed on them.

At the beginning of the article, it was mentioned that almost any low-rise building can be built on a buried strip foundation, but this is not always advisable. Let's see why? Let's take for example a small wooden house for which the foundation was calculated in the article and try to calculate the tape for it. It turns out that its minimum allowable width will be only 7.1 cm. And you will have to do at least 20 cm. The overspending of only one concrete will be almost 200%, not to mention all related materials and work. Obviously, a columnar foundation in this case would be a better choice.

Thus, we have more or less figured out the calculation, now directly about the technology itself.

Stages of erection of a buried monolithic strip foundation.

1) What to dig - trenches or a foundation pit?

Sometimes the answer to this question is very simple. For example, if you are going to build a house with a basement, it is obvious that you need to dig a foundation pit. But if the basement is not planned, what then?

And then you need to take into account the features of your project, your building site, the possibility of mechanizing work and decide on your own (well, or on the advice of a more experienced builder friend). What you need to pay attention to:

• Type of soil on the site, especially its flowability - you must admit, it is problematic to dig a trench with even walls that do not crumble at the slightest touch in dry sandy soil. In addition, with great depth and manual work, it simply becomes an unsafe occupation.
• The thickness of the fertile layer- this is especially true if you are going to make floors on the ground. The fertile layer will need to be completely removed, because. it tends to decrease in volume over time due to decay processes. And due to the fact that in some regions of our country this layer is very thick, digging a foundation pit with its subsequent backfilling with non-porous material (sand) becomes inevitable.
• Required width of the sole of the tape- it's one thing if the calculation requires a width of 20-30 cm, another if it's 50-60 cm. Filling the entire tape to such a width is a rather costly undertaking. It can be made already with an extension at the base, but for this it is necessary to build a formwork. Fiddling with formwork in a narrow deep trench is extremely inconvenient, so sometimes it's really easier to dig a pit.

2) Preparation and marking of the site.

Before starting construction, it is necessary to carry out measures to divert surface rainwater from the building site. It is not necessary to pour concrete into soil that has become muddy after rain, and no one is safe from bad weather. Given the terrain, dig small drainage trenches if necessary.

Try to bring the necessary building materials to the site before excavation. The shorter the cycle of foundation work (up to the construction of the blind area), the better.

The marking of the site will be discussed in detail in a separate article.

3) Further work order depends on whether we are going to pour concrete directly into the ground or into the formwork.

When pouring into a trench, you must:

1. level and clean the bottom of the trench;
2. lay insulation, if insulation of the foundation is required;
3. cover the trench with a layer of rolled waterproofing;
4. make concrete preparation - pour at least 5 cm of lightweight concrete on the bottom of the trench and let it harden (this prevents damage to the waterproofing layer by reinforcement and protects it from corrosion due to contact with the ground);
5. install a reinforcing cage on the concrete preparation that has set, lay household communications;
6. build a leveling plinth formwork;
7. to pour concrete.

When pouring into the formwork, the sequence is different:

1. level and clean the bottom of the trench or a section of the bottom of the pit under the future foundation;
2. mount the formwork;
3. make concrete preparation;
4. install a reinforcing cage, lay household communications;
5. pour concrete;
6. dismantle the formwork;
7. make waterproofing of the foundation;
8. make insulation of the foundation;
9. backfill the soil.

In the near future, a separate detailed article will be devoted to each main stage of foundation construction, such as, formwork, reinforcement, because. they all require special personal attention. And now at the end of a few more general recommendations:

• carefully level and compact the base under the foundation tape, especially if this is done after the operation of the excavator. The sole must be flat and strictly horizontal. If there is no construction level, control the hydraulic level (it costs a penny, it is sold at any hardware store);
• for insulation, use extruded polystyrene foam (EPS) with a thickness of 50-100 mm. Styrofoam is not suitable for these purposes. When laying insulation in a trench, you can attach it to the side walls, for example, with plastic umbrellas (fungi) or simply with pieces of thick wire, sticking it into the ground through the EPS. For temporary fixation before pouring concrete, this is quite enough;
• when covering the trench with waterproofing, make sufficient overlaps (about 20 cm). An extra roll won't save a lot of money;
• when mounting the reinforcing cage, use a knitting wire or plastic clamps. Welding is not recommended in this case;
• the formwork must be strong and reliable. The buried strip foundation is quite high and when pouring concrete, it will experience tremendous pressure. Cases of formwork rupture are not uncommon in construction, especially when the concrete is compacted with a good industrial vibrator;
• fill the tape with a mixer. A recessed strip foundation is a very massive structure, so in the example discussed above (the foundation for a 2-storey house 24 cm wide), the volume of the concrete mixture will be almost 17 m³. It is simply unrealistic to pour them yourself from a conventional concrete mixer so that unacceptable layer-by-layer hardening does not occur;
• when pouring, it is advisable to use a vibrator for concrete, in extreme cases, do the bayonet with a pointed piece of reinforcement. Also, for better air removal, you can knock on the formwork with a small sledgehammer, unless of course you are sure of its strength;
• formwork can be removed and waterproofing can be done approximately 3-7 days after pouring (depending on the weather - the hotter and drier, the faster).
• backfilling of a buried strip foundation can be done with native previously excavated soil with its layer-by-layer compaction. The use of coarse sand here, as in the construction of a shallow foundation, is no longer important;
• try not to delay the construction of the blind area.

For now, let's stop there. We will be glad to see your questions and especially your personal experience in the comments.

Structural for reinforced concrete beams, the minimum width is allowed 15 cm, and for shallow strip foundations (which are free-lying beams on an elastic foundation), a width of at least 25 cm for light garden buildings, and a width of at least 30 cm for country houses. The width of a strip shallow foundation cannot be less than the width of the wall supported on it.

However, in addition to structural limitations, there are also requirements set by bearing capacity of soils under shallow strip foundations. The specific load from the building per unit area should not exceed 70% from the bearing capacity of the soil. You can regulate the amount of load using the area of ​​\u200b\u200bsupport of the foundation on the ground. The larger the support area, the lower the specific load transferred to the ground.

Approximate calculation method for the minimum sufficient width of a shallow strip foundation. This method for determining the minimum sufficient width of a shallow strip foundation is based on the idea that the value of the specific load per unit area of ​​the soil under the foundation should be less than the bearing capacity (calculated base resistance) of the soil under the foundation. The difference between the load from the house and the bearing capacity of the soil must be at least 30 percent greater in favor of the bearing capacity of the soil (factor of safety for concrete structures cast on site with a specific weight of less than 1600 kg/m3). In order not to tire the most impatient readers, who are finally in a hurry to find out without too much sentimentality the minimum sufficient width of a shallow strip foundation, we publish a table based on data from the British State Building Code Building Regulations Approved Document A: 2010, 2E3, Table No. 10. The British Architectural Office calculated everything for us in advance, and we tried to average and adapt the presented data a little to make the data presentation more convenient:

Now, the most adventurous and less curious readers can run to cast their shallow cast-in-situ strip foundation, and the rest can find out how the British got this data and make their own more accurate calculation for their own home, so as not to get into a mess.

To determine the minimum sufficient width of a shallow-depth strip foundation based on the bearing capacity of the underlying soils, it is necessary to solve the equation:

Dead weight of the building is the sum of the weights of all the building elements of the house structure. To calculate them, you need to use the following tables:

Table No. 6Load from 1 m 2 spans up to 4, 5 m

Table number 7Table of the amount of timber in m 3 lumber

Table No. 8Table of the number of boards in a cubic meter of lumber

Table No. 9Tableroofing weight values

Table No. 11 Load from 1 m 2 of the horizontal projection of the roof