It is a platform made of reinforced concrete, designed to evenly distribute the load that is created by the foundation of the house on the ground. The width of the footing is usually at least twice the width of the foundation. Footing structures are required by most local building codes for foundation installations on loose sandy and silty soils.

Most of the foundation footings we construct are 30 cm high and 60 cm wide. Typically, unless the design specifies otherwise, we reinforce such a footing with two rows of 12 mm diameter steel reinforcing bars. In our case, the soil at the bottom of the pit was such that for a two-story house with plan dimensions of 8x12 m, it was impossible to do without an additional base that would increase the area of ​​support for the foundation. For the Leningrad region, where we work, this is a common occurrence.

Before starting to build the base, it was necessary to mark the exact location of the house foundation on the bottom of the pit.

We always rely on the markers installed by surveyors when marking the construction site before the excavation begins. Usually, at the bottom of the pit, it is enough to determine the position of two base points - the two extreme corners of one of the foundation walls. In most cases, we find the position of these corner points using a cord, stretching it between the poles installed by surveyors and a plumb line. We hammer in two of our stakes along the plumb line at the bottom of the pit, using scraps of reinforcement for this purpose, so as not to remove them when it comes to pouring concrete. The distance between these two poles must exactly correspond to the length of the wall indicated by the architect on the plan.

To quickly mark the position of the other two corners of the foundation, you need to calculate the length of its diagonal. This is not that difficult to do with a regular calculator. And knowing the length of the diagonal and the dimensions of the foundation in plan, you can easily and accurately determine the position of the remaining two corners and mark them with poles. We do this as follows. Two members of the team hold the ends of the tape of two tape measures at the base points already marked with stakes, while the third member of the team, pulling the tapes of both tape measures, crosses them at the marks of the length of the diagonal and the length of the wall, and at the point of intersection hammers another pole into the ground. To eliminate possible errors, we always double-check the distances between all the stakes driven into the bottom of the pit, checking them with the dimensions indicated on the plan. After the poles are hammered into all corners, we pull the cord from one corner to the other and get the outline of everything strip foundation entirely.

Now, having installed all the poles, you can begin constructing the formwork. For this we use boards with a cross-section of 5x30 cm, connected to each other using steel U-shaped brackets driven into the ground, which hold the inner and outer walls of the formwork at a distance of exactly 60 cm from each other.

We install the formwork in such a way that the foundation walls are located exactly in the center of the base (the width of the foundation walls of this house according to the project was 25 cm). We begin work on the construction of the formwork by fastening two boards with a cross-section of 5x30 cm at an angle of 90° with nails to form an outer corner and installing them at a distance of 17.5 cm from the cord. Then, parallel to the boards of the external formwork, we install and We fix the boards of the inner wall of the formwork using steel U-shaped brackets. So, gradually moving from one corner to another, we continue this process until the installation of all external and internal walls of the formwork is completed.

We place U-shaped brackets securing the formwork in straight sections in increments of 100-120 cm. At the junction of two boards, we connect their edges using nails driven at an angle and install fastening brackets on both sides of the joint.

We rarely have to adjust and cut formwork boards to length. When, for example, two boards do not join tightly enough, we close the gap using a short overhead board, nailing it from the outside. And if one or another board turns out to be a little longer than necessary, we simply nail it to the adjacent board with an overlap. We simply do not pay attention to the small irregularities that form on the side edges of the sole. In the end, it is not the appearance of the sole that is important, since it will still be completely buried in the ground. The main thing is that the finished sole has strength not lower than the design one and successfully copes with the functions assigned to it.

Once the formwork is fully installed, we carry out partial backfilling of soil near its potential weak points, for example, at the junction of individual boards or in areas where it was impossible to install U-shaped fastening brackets. In addition, backfill prevents concrete from seeping under the formwork and lifting it.

Next, using a theodolite, we establish the level of the upper edge of the foundation base. It must be located, firstly, strictly horizontally, and secondly, exactly at a given depth indicated on the plan by the architect. We fix the level marks with small nails 02.5x50 mm, hammering them in half their length at a distance of 0.5-1.0 m from each other along the entire perimeter from the inside of the formwork boards. When laying concrete, they serve as a guide for us to determine to what height the formwork should be filled.

Now everything is ready to lay the concrete. The best pits are those that can be easily reached by a concrete truck at any point. But, unfortunately, this happens very rarely. Therefore, we usually start laying from the areas that are most difficult for a concrete truck to reach, moving concrete along the formwork with shovels until these areas are filled to the required height - to the level of the nails that fix the height of the foundation base.

After pouring concrete into the formwork is completed, we proceed to reinforcing bars 012.5 mm. To do this, we first lay out the reinforcement bars in two rows on top of the wet concrete at a distance of approximately 15 cm from each wall, sliding them under the crossbars of the U-shaped brackets. And then we sink them into concrete to a depth of about 20 cm, using ordinary bayonet shovels as a tool. We carefully and carefully “pierce” the concrete above the recessed reinforcement bars with the same shovels to remove the air that has gotten into it.

Having leveled the concrete surface to the height of the nails that fix the level of the upper edge of the sole, we carefully lift all the steel U-shaped brackets a few centimeters. Usually 5-7 cm, no more, in order to easily perform the last two operations. The first of them is grouting the upper edge of the sole. In addition to facilitating all subsequent work on the construction of foundation walls, the smooth surface facilitates the removal of dirt and debris that inevitably falls on the upper edge during dismantling of the formwork. Finally, the final step in constructing the footing is cutting or extruding a keyway along the center centerline of the top edge. This groove should ensure strong and reliable adhesion of the sole to the foundation wall that will be built on it in the future. Typically we make a keyway 2.5-3.0 cm deep and 7-8 cm wide by simply pressing a short block of appropriate cross-section into the concrete along the center line of the top edge of the sole. By the time this work begins, the concrete has usually already hardened sufficiently, so the block leaves behind a groove, which itself does not “float” and does not change its shape and size. We make such grooves only on straight sections of the base, not bringing them to the corners by about 0.5-0.7 m. Since the corners are the strongest parts of the foundation wall, there is no need to worry about violating the integrity of the foundation at these points.

Before removing the formwork, we transfer from it the position marks of the corners of the foundation walls directly to the upper edge of the base, drawing marks with the tip of a nail on the slightly hardened surface of the concrete. They will serve as a guide for installing the formwork when constructing the foundation walls.

Support sole is a stepped expansion at the bottom of the strip foundation structure. It is used in the construction of foundations for heavy buildings erected on weak-bearing heterogeneous soils. This sole allows you to distribute the weight of the structure more evenly, thereby reducing pressure on the ground. Depending on the magnitude of the loads, as well as the size of the building and the characteristics of the soil, the foundation on the supporting base can be single-stage, two-stage, or three-stage.

Construction of a strip foundation with a support base

The design of this foundation is not particularly complicated. The walls of the building being erected rest on a strip support, which is buried in the ground. The tape is laid under all the internal and external walls of the building, while maintaining its identical cross-section along the entire perimeter of the foundation. All these tapes together create a foundation that transfers the load to the ground.

buried to a depth of 30 cm below the soil freezing level. Such a foundation can be made of various materials, such as:

Rubble or brickwork;

Monolithic concrete;

Reinforced concrete blocks.

In modern construction the most common are monolithic concrete strip foundations. While foundations made of rubble stone and brick, although they were widespread in the middle of the last century, today have already lost their relevance. In turn, prefabricated foundations made of reinforced concrete blocks are used in large-scale construction, because this technology requires the use of special construction equipment.

Advantages of a strip foundation with a support sole:

Ease of construction;

High durability;

High load-bearing capacity;

Used for a wide variety of soil types;

Suitable for any buildings;

There is an opportunity to arrange a basement.

Disadvantages of a strip foundation with a supporting sole:

It is impossible to build on deeply frozen and highly intumescent soils;

A foundation made of monolithic concrete will require more time and labor compared to other types of foundations;

High consumption of materials (formwork, reinforcement or concrete);

For buried types of strip foundations, the use of special construction equipment is required;

High cost of foundation construction.

Even with all the existing shortcomings, strip foundation with support base is the most popular and widespread in modern construction. By choosing this type of strip foundation, you guarantee your future construction high reliability and durability.

Prices for strip foundations

The cost of building a strip foundation with a support base includes:

Terrain marking, georeferencing;

Digging a trench for the foundation 10 cm;

Sand cushion 10-20 cm, compacted;

Installation of reinforcement cages;

Installation of formwork;

Pouring concrete grade M250.

№	Foundation type	Unit of measurement	Cost in rubles
1	Shallow strip foundation	m/n	4400
2	Recessed strip foundation	m/n	7000
4		m/n	7600

For an additional fee you can order:

• Change of concrete grade M300-M450
• Increasing the diameter of the reinforcement
• Changing the height or width of the strip foundation

Calculation of foundation width, sole, supporting part - relevant when choosing a reinforced concrete monolithic strip as the main foundation. If the supporting part of the foundation is calculated incorrectly, then the weight of the house will exceed the resistance of the soil, and the house will push the soil underneath it. In this case, shrinkage, as a rule, occurs unevenly, and, as a result, structural cracks will appear on the foundation and masonry walls.

How to correctly calculate the foundation yourself, spending a minimum of time on this? Moreover, statistics show that more than 70% of private developers do not order calculations from designers, but select the type of foundation and its characteristics at their own peril and risk.

Calculating the base of the foundation in this article will allow you in 5 minutes to get all the necessary values ​​for choosing the optimal foundation for your house.

The calculations below alone do not guarantee the reliability of the foundation. In addition to the correct calculation of the foundation, a professional design solution (QS), high-quality construction, reliable conservation of the foundation with anti-heaving measures (if the foundation remains unloaded in winter) and proper operation of the house are necessary. Only if all these conditions are met will the foundation be reliable and durable.

The main task of the foundation- accept the loads from the house, partially redistributing them within its thickness and transfer them as evenly as possible to the soil foundation located under the foundation. Therefore, in the formula for calculating the foundation base:

S foundation supports > P 1 (house weight) / P 2 (soil resistance) x 1.2 - the following indicators are presented:

1. House weight P 1 (ton/m2) - the force with which the house presses down on the ground;
2. Reliability factor 1.2- a value indicating the ability of a structure to withstand loads applied to it above the calculated ones provided for by the standards. The presence of a safety margin provides additional reliability of the structure to avoid damage and destruction in the event of possible design, manufacturing or operating errors.
3. Ground resistance force P 2(kg/cm 2) - reverse force directed from bottom to top. It is not recommended to multiply this value by additional coefficients, because this will lead to a reduction in the area of ​​the foundation base, reducing its load-bearing capacity.

To determine the resistance force of the soil, it is necessary to know its composition. You don't have to do geology for this. It is enough to dig a hole up to 1.5 m deep in the area and examine the soil tactilely and visually. The most common load-bearing soils in the Moscow and Leningrad regions are: 1) Clay; 2) Loam - if it is a clayey rock mixed with sand, where clay predominates; 3) Sandy loam - if there is sand mixed with clay, where sand predominates; 4) Sand.

For calculations, we will use average values ​​that show what resistance a particular soil has, i.e. what bearing capacity the soil can provide on the site for building a house.

P 2 clay = 6 kg/cm 2

P 2 sand = 4 kg/cm 2

For convenience and speed of calculations, we divide the constant values ​​and get:

1.2 reliability factor / P 2 clay = 0.2

1.2 reliability factor / P 2 sand = 0.3

From here we derive the formula calculation of the foundation area based on the weight of the house:

For clay: S foundation supports > P 1 (house weight) x 0.2

For sand: S foundation supports > P 1 (house weight) x 0.3

How to determine the weight of the house P 1? To do this, select the main material for wall construction, then the weight category load factor from the table below:

Load factors take into account all additional loads during operation of the house.

Calculation of strip foundation example:

Example 1.

Initial data. Typical design of a one-story aerated concrete house No. 62-09 with a total area of ​​113.09 m 2. The building area is 157.14m2. Finishing: façade plaster. Length of load-bearing walls, including internal walls = 79.64 m. The load-bearing soil on the site is clay.

P 1 weight of the house = 157.14 x 2 = 314.28 tons. Before putting it into the formula, we convert tons to kg. We get the weight of the house = 314,280 kg

S foundation supports = P 1 (house weight) x 0.4 = 314,280 x 0.4 = 125,712 cm 2 = 12.57 m 2

12.57 m2 - this is the required (S norm - normative) foundation support area for this specific project and construction conditions, necessary to solve its main problem (see at the beginning of the article).

P - perimeter, the total length of all load-bearing walls according to the project is 79.64 m.

S fact = P x T = 79.64 x 0.4 = 31.86 m 2

We compare 2 numbers and get: S fact > S norms. That. This foundation is 2.5 times higher than the standard values, therefore it fully complies with the necessary requirements.

Example 2.

Initial data. Typical design of a two-story attic house No. 62-09 with a total area of ​​113.6 m 2. The building area is 93.57m2. The material of the load-bearing walls is 400mm aerated concrete. Finishing: façade plaster. Length of load-bearing walls, including internal walls = 59.17 m. The load-bearing soil on the site is sand.

According to the table, the house corresponds to the 2nd weight category. We get:

P 1 house weight = 93.57 x 2 = 187.14 tons. Because 2-storey house multiply 187.14 x 2 = 374.28 tons. Before putting it into the formula, we convert tons to kg. We get the weight of the house = 374,280 kg

S foundation supports = P 1 (house weight) x 0.6 = 374,280 x 0.6 = 224,568 cm 2 = 22.57 m 2

14.97 m2 - this is the required (S norm - normative) foundation support area for this specific project and construction conditions, necessary to solve its main problem (see at the beginning of the article).

The next step is to check whether the actual area of ​​the strip foundation corresponds to the standard area. S fact ≥ S norms

P - perimeter, the total length of all load-bearing walls according to the project is 59.17 m.

T - the thickness of the strip foundation walls must be no less than the thickness of the load-bearing walls. In this project it is = 0.4 m.

We calculate the actual area S fact of the strip foundation:

S fact = P x T = 59.17 x 0.6 = 35.5 m 2

We compare 2 numbers and get: S fact > S norms. That. This foundation exceeds standard values ​​and therefore fully complies with the necessary requirements.

Note. When calculating the area of ​​a pile-grillage foundation, 2/3 of the area should fall on the heels of the columnar foundation (piles).

In accordance with SNiP2.02.01-83, the condition for carrying out calculations for deformations (for the second limit state) is to limit the average pressure at the base of the foundation p the value of the calculated resistance R:

p £ R, (6.4)

Where p– average pressure under the base of the foundation, kPa;

R– design resistance of the foundation soil, kPa.

This condition must be met with an underload: for monolithic foundations - £5%, for prefabricated foundations - £10%.

The fulfillment of the condition is complicated by the fact that both parts of the inequality contain the required geometric dimensions of the foundation, as a result of which the calculation must be carried out using the method of successive approximations over several iterations.

The following sequence of operations is proposed when selecting the size of the foundation:

Þ are specified by the shape of the foundation base:

If the foundation is strip, then a strip section 1 m long and 1 m wide is considered b.

If the foundation is rectangular, then the aspect ratio of the rectangle is specified in the form h=b/l= 0.6…0.85. Then A=bl=b 2 /h, Where A– area of ​​the rectangle, l- length, b– width of the rectangle. From here. A special case of a rectangle is a square, in this case

Þ calculate the preliminary area of ​​the foundation using the formula:

Where N II– sum of loads for calculations for the second group of limit states, kPa. In the case of strip foundations, this is a linear load; in the case of rectangular and square foundations, this is a concentrated load;

R0– tabular value of the calculated resistance of the soil where the base of the foundation is located, kPa;

g¢ II– averaged calculated value of the specific gravity of soils lying above the base of the foundation, kN/m 3 ;

d 1– the depth of laying the foundations of basement-free structures or the reduced depth of laying external and internal foundations from the basement floor:

Where h s– thickness of the soil layer above the base of the foundation on the basement side, m;

h cf– thickness of the basement floor structure, m;

g cf– calculated value of the specific gravity of the basement floor structure, kN/m 3 ;

Figure 6.6: To determine the depth of foundations

A- at d 1<d; b – at d 1>d; c - for slab foundations

1- outer wall; 2 - overlap; 3 - internal wall; 4 - basement floor; 5 - foundation

Þ Based on the known shape of the foundation, calculate the width of the foundation:

in case of strip foundation b=A¢;

in the case of a square foundation;

in the case of rectangular and l=h/b.

After determining the required dimensions of the foundation, it is necessary to design the body of the foundation in the explanatory note in the form of a sketch with dimensions. In this case, the dimensions of the foundation can be varied within small limits based on the design considerations set out in clause 6.2.1. Only after clarifying all the dimensions of the foundation can you move on to the next point.

Þ using formula (7) SNiP 2.02.01-83 calculate the design resistance of the foundation soil R:

Where g с1 And g c2– coefficients of working conditions, taking into account the characteristics of different soils at the base of foundations and taken according to Table 6.14;

k– coefficient accepted: k=1 – if the strength characteristics of the soil ( With And j) determined by direct tests and k=1.1 – if they are adopted according to SNiP tables;

k z– coefficient accepted k z=1 at b<10м; k z=z 0 /b+0.2 at b³10m (here z 0=8m);

b– width of the foundation base, m;

g II And g¢ II– averaged calculated values ​​of the specific gravity of soils lying respectively below the base of the foundation (in the presence of groundwater is determined taking into account the weighing effect of water) and above the base, kN/m 3 ;

with II– calculated value of the specific adhesion of the soil lying directly under the base of the foundation, kPa;

d b– basement depth – distance from the planning level to the basement floor, m (for buildings with a basement width B£20m and depth over 2m accepted d b=2m, with basement width B>20m accepted d b=0);

M g, Mq, M c– dimensionless coefficients taken according to Table 6.15;

d 1– depth of laying foundations for basement-free structures or reduced depth of laying external and internal foundations from the basement floor (see previous paragraph), m.

Table 6.14

Coefficient values g с1 And g c2

Soils	g с1	g c2 for buildings and structures with a rigid structural design when the ratio of their length (or an individual compartment) to the height L/H
³4	£1.5
Coarse clastics with sandy filler and sandy ones, except for small and silty ones	1,4	1,2	1,4
Sands are fine	1,3	1,1	1,3
Silty sands: low-moisture and wet saturated with water	1,25 1,1		1,2 1,2
Silty-clayey and coarse-clastic with silty-clayey filler, with the fluidity index of the soil or filler: I L£0.25	1,25		1,1
The same, at 0.25< I L£0.5	1,2		1,1
The same, with I L >0,5

Notes:

1. Buildings and structures are considered rigid if their structures are adapted to withstand additional forces from base deformations.

2. In buildings with a flexible design, it is accepted g c2=1.

3. For intermediate values ​​of the ratio of the length of a building or structure to its height L/H coefficient g c2 determined by interpolation.

Table 6.15

Coefficient values M g, Mq And M c

j II, hail	M g	Mq	M c	j II, hail	M g	Mq	M c
			3,14		0,72	3,87	6,45
	0,03	1,12	3,32		0,84	4,37	6,90
	0,06	1,25	3,51		0,98	4,93	7,40
	0,1	1,39	3,71		1,15	5,59	7,95
	0,14	1,55	3,93		1,34	6,35	8,55
	0,18	1,73	4,17		1,55	7,21	9,21
	0,23	1,94	4,42		1,81	8,25	9,98
	0,29	2,17	4,69		2,11	9,44	10,80
	0,36	2,43	5,00		2,46	10,84	11,73
	0,43	2,72	5,31		2,87	12,5	12,77
	0,51	3,06	5,66		3,37	14,48	13,96
	0,61	3,44	6,04		3,66	15,64	14,64

Þ we determine the actual stresses under the base of the foundation:

Reactive soil pressure along the base of a rigid centrally loaded foundation is assumed to be uniformly distributed, kPa:

, (6.8)

Where N II– standard vertical load at the level of the foundation edge, kN;

G fII And G gII– the weight of the foundation and soil on its ledges (to determine the weight, it is necessary to determine the volume of the foundation or soil body and multiply it by the specific gravity), kN;

A– area of ​​the foundation base, m2.

Eccentrically loaded A foundation is considered to be one in which the resultant of external loads does not pass through the center of gravity of the area of ​​its base. Such loading is a consequence of the transfer of moment or horizontal component of the load to it. When calculating, the pressure along the base of an eccentrically loaded foundation is assumed to vary according to a linear law, and its boundary values ​​under the action of a moment of force relative to one of the main axes are determined as for the case of eccentric compression:

, (6.9)

Where M x , M y– bending moments relative to the main axes of the foundation base, kNm;

W x , W y– moments of resistance of the section of the foundation base relative to the corresponding axis, m 3 .

The pressure diagram under the base of the foundation obtained using this formula should be unambiguous, i.e. over the entire width of the section, the stresses must be compressive. This is due to the fact that tensile stresses, if they occur, can lead to separation of the base of the foundation from the base and a special calculation will be required, which is not included in the scope of the course project.

Þ The load-settlement relationship for shallow foundations can be considered linear only up to a certain limit of pressure on the foundation. The calculated resistance of the foundation soils is taken as such a limit R. Condition fulfilled p=R corresponds to the formation in a homogeneous base under the edges of the foundation of minor, deep z max@b/4, areas of limiting stress state (areas of plastic deformation) of the soil, allowing, according to SNiP, the use of a model of a linearly deformable medium to determine stresses in the foundation.

The applicability of the model of a linearly deformable medium is ensured by the following conditions:

* For centrally loaded foundations:

p<R, (6.10)

* For eccentrically loaded foundations:

p<R,

p max<1.2R(6.11)

* For eccentrically loaded foundations with bending moments in two directions:

p<R,

p max<1.2R

p with max<1.5R(6.12)

In most cases, after the first iteration, this condition is not met with the required tolerance (exceeding R over p up to 5%). All operations must be repeated completely, substituting into the formula for A¢ instead of R0 the value of the calculated resistance R. Calculate A, b, select a foundation with a new value b, define a new value R, calculate p and check the condition again p<R.

Typically, as a result of the second iteration, the condition p performed in 70% of cases. If the condition is not met, repeat the calculation again.

With strip foundations, when the width of the slabs coincides with the calculated width, it is allowed to replace rectangular slabs with slabs with corner cutouts. In this case, the slabs (of any shape) are laid in the form of a continuous strip. If the calculated width does not coincide with the width of the slab, intermittent foundations are designed.

Based on the established depth, shape and dimensions of the foundation base, the foundation is constructed using prefabricated reinforced concrete and concrete foundation structures or monolithic concrete structures.

Accompany the calculations with the necessary sketches.

Features of calculating intermittent foundations:

When constructing buildings that are not subject to increased rigidity requirements, on strong soils (dense and medium-density sand; hard, semi-solid, refractory silt-clay) with the groundwater level below the base of the foundation, it is permissible to use intermittent strip foundations, which are constructed from slabs located at some distance from each other. It is especially advisable to use such foundations in cases where the calculated width is less than standard slabs.

Figure 6.7: Discontinuous foundation

1 – soil surface; 2 – concrete blocks; 3 – foundation slabs; 4 – spaces between slabs filled with soil

Discontinuous foundations made of rectangular slabs and with corner cutouts are not recommended:

* in soil conditions of type II in terms of subsidence;

* when there is loose sand under the base of the foundation;

* if the seismicity of the area is 7 points or more; in this case, it is necessary to use slabs with corner cutouts, laying them in the form of a continuous strip;

* when silt-clay soils with a fluidity index occur below the base of the foundation I L>0,5.

Due to the distributive capacity of soils and the arch effect, the pressure under the base of intermittent foundations at shallow depths is equalized and we can assume that they operate as continuous foundations. Therefore, their width is determined, the design resistance is assigned, and the settlement is calculated as for continuous strip foundations without deducting the areas of the gaps.

Optimal spacing between slabs C assigned from the condition of equality of the calculated soil resistance R obtained for a strip foundation with a width b, soil resistance obtained for a discontinuous foundation R p with slab width b p, length l p, with the operating conditions coefficient k d:

, (6.13)

The operating conditions coefficient depends on the condition of the soil (for intermediate values ​​it is determined by interpolation):

* k d=1.3 – for sands with porosity coefficient e@0.55 and silty clay soils with a fluidity index I L £ 0;

* k d=1 – for sands with porosity coefficient e@0.7 and silty clay soils with a fluidity index I L=0,5;

Based on the working conditions of the foundation soils and wall blocks, the interval between the slabs should be C£(0.9…1.2)m and no more than 0.7× l p, and the width of the slab should be b p£1.4 b. For more efficient use of discontinuous foundations, the number of intervals can be increased by using shortened slabs (1180 and 780 mm), if this does not entail an unjustified increase in labor costs.

The classic foundation base, which can be seen in many residential buildings today, is designed in such a way as to evenly distribute the load of the house's foundation onto the ground surface. This structure looks like a reinforced concrete platform with a width at least twice the width of the foundation itself.

The extreme necessity of constructing the base of the foundation is the situation when the foundation will be installed on loose sandy soil or with silty soil.

How to calculate the size of the foundation base?

The size of the foundation base is calculated using the formula below.

• Sf =1.1 x (Md: Rg);
• Sf – area of ​​the foundation base;
• Md – approximate mass of the future building;
• Рг – soil resistance (we take information from the table);
• 1.1 is a typical safety factor for low-rise buildings.

Over many years of world construction practice, it has been revealed that in order to increase the strength of the foundation, it is necessary to increase the width of its base. must have half its width, and the width of the sole must be at least 200 mm greater than the thickness of the foundation wall.

The construction is good and needs special installation. It is very important that the sole is located much below the freezing depth. This condition must be met in order to further protect the building from movement on muddy soil.

To determine the parameters of the foundation as accurately as possible, a huge number of factors should be taken into account, the most important of which are:

• condition and type of soil;
• building design;
• brand of concrete;
• the amount of reinforcement used.

The construction of a house begins with the foundation, which is why it is very important to understand the full degree of responsibility and the importance of correct preliminary calculations and measurements. We advise you to leave this matter to professionals in order to subsequently avoid such troubles as subsidence and cracking of the base. The right ones will help avoid this.

Before starting the construction of the foundation base, you should decide on the tools and materials that will be used. The most important and necessary items that will definitely be useful for constructing the base of the foundation include:

• shovel - for excavating a trench;
• bayonet shovel - for working with reinforcing bars;
• fittings or wire;
• hook (tool for tying reinforcement);
• hammer;
• nails;
• wooden beams;
• level or hydraulic level;
• 2 nylon laces;
• concrete;
• boards with a section of 5×30 cm;
• poles.

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Preparatory work: installation of poles

When the dimensions of the foundation are known, you can proceed to the next stage. Before you begin the actual construction of the base of the foundation, you need to make a marking at the bottom of the pit, indicating the clearest possible location of the foundation of the building.

The most convenient way to navigate is by the markers that surveyors installed during the process of marking the construction site even before the foundation pit was dug.

We find the position of the corner points at the bottom of the pit using a nylon cord, pulling it between the poles and plumb line that were installed by surveyors.

At the very bottom of the pit, along its steep part, you need to hammer in a couple of pegs. To do this, we recommend using scraps of reinforcement, since they will not need to be removed during the concrete pouring process. The distance between this pair of poles must correspond exactly to the length of the wall, which was determined and indicated on the architectural plan.

In order to quickly finish marking the pair of remaining corners, we first advise you to calculate the size of their diagonal. You can make such a calculation yourself, but it will take a lot of time to make calculations and markings, not to mention the process of construction itself. In view of saving time, it is advisable to hire a couple of specialists who have experience in performing these tasks.

It is best to calculate the dimensions of the foundation with the help of three team members. The procedure will be as follows: at key points that have already been marked with vertices, two people fix and firmly hold the outer parts of the tapes from two tape measures. At the same time, a third person pulls the tapes of these tape measures so that the tapes intersect to indicate the length of the diagonal and the length of the wall. At the point where the tapes intersect, another stake must be driven into the ground.

In order to control the clarity and correctness of the work done, it is necessary to check the distance between all the poles several times. The last thing to do is to pull the cord between the two corners, resulting in the outline of the future strip foundation.

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Construction of formwork

Once the process of installing the poles has been completed, you can begin to construct the formwork itself. For these purposes, it is advisable to use boards with a cross-section of 5x30 cm, connected to each other by means of metal brackets driven into the ground. The brackets are shaped like the letter “P” and perform the function of holding the inner and outer walls of the formwork. The optimal distance is about 16 cm.

The formwork must be installed so that the foundation walls are distributed exactly in the very center of the base. Next, we fasten together (at an angle of 90°) two boards with a cross section of 5x30 cm and place them from the cord at a distance of 17.5 cm. A similar algorithm is carried out to form an outer corner.

After completing these steps, it is necessary to install and secure the boards for the inner wall of the formwork. On both sides of the joint of the boards, with a step of about 100 cm, we install brackets in the shape of the letter “P”.

If the boards do not fit together tightly enough, we recommend sealing the connector using a small overhead board, nailing it from the outside. If the opposite situation arises, the board turns out to be larger than expected, then you simply need to nail it to the adjacent board with an overlap.

The boards need to be leveled and adjusted, because this factor greatly affects the strength of the sole and how it will subsequently perform its functions.

After installation is completed, the weakest areas of the formwork must be partially covered with soil. The weak points of the formwork can be either the places where the boards join, or the places where there are no staples. This kind of backfilling of soil will prevent concrete from getting under the formwork.

After completing all of the above steps, it is necessary to establish the highest level of the edge of the foundation base. This is done using a theodolite. When determining the level, it is imperative to make small clamps with nails, driving them 50% of the length at a distance of 1 m from each other. In the future, such small guidelines will play into the hands of the concrete laying process.