Strip foundation is the most common type of foundation for building a house. Therefore, everything is clear with him, but how does a shallow (MZLF) differ from it - a shallow foundation, how to calculate and how to do it?
Characteristics - design principle of operation
A shallow strip foundation or simply MZLF is similar in its laying method to its counterpart, but has important differences:
- foundation laying depth up to 700 mm;
- located above the zone of soil freezing;
- designed for arrangement on swollen (heaving) soils.
The main feature of a shallow strip foundation is that it makes it possible to level the frost heaving of the soil. This is due to the fact that, despite the general rigidity of the structure, the MZLF, along with the weight of the entire structure, moves up and down depending on the time of year. Since the foundation is not deeply deepened, but is displaced evenly, then, therefore, it does not collapse from such vibrations.
Scheme of the device of a shallow strip foundation
- Sand and gravel pad
- Foundation tape
- waterproofing layer
- Vertical (or coating) waterproofing
- Armature (diameter 12)
- Armature (diameter 8)
- plinth
- Wall
Where to use - application
A strip shallow foundation is suitable for the construction of low-rise residential buildings and other structures from those materials that will not create significant pressure on the base of the foundation. Such structures and materials include:
- log cabins;
- cellular concrete - foam concrete, gas silicate blocks;
- lightweight bricklaying;
- frame-panel buildings.
When arranging a foundation of greater width, it is possible to build heavy houses from a bar or log on it. But in this case, the soil will freeze to a lesser depth and there is a possibility of deformation of the foundation. Thus, if it is planned to build a monumental building, it is better to equip a tape monolithic foundation.
At the same time, you should be aware that an increase in the width of the tape of shallow foundations makes it possible to build heavier houses with an attic. The large width of the foundation tape (respectively, the basement) helps to reduce the depth of soil freezing in the space under the floor.
What should be considered when constructing a shallow foundation
Shallow foundations are laid on heaving soils
It is forbidden to fill MZLF on biogenic organic soils, for example, peat, sapropel (deposits of freshwater reservoirs), as well as on clay. The photo shows that already their appearance does not bode well.
- groundwater level
The closer the water is to the surface of the earth, the more unstable the MZLF will be.
If the terrain is characterized by a significant difference in height (a house on a slope), then the installation of a shallow strip foundation on it is quite problematic. In this case, an ordinary strip foundation is equipped or a significant area under the MZLF is leveled. In terms of time and money, both options are equivalent.
- Depth
It represents the height from the lowest point of the foundation, the so-called sole, to the zero mark (ground surface).
- Climate (depth of soil freezing)
It is quite common among builders to lay a shallow strip foundation at a height, which is calculated by the formula - freezing depth minus 20%. So you can be sure that the foundation will rise with the structure.
The minimum depth of a shallow strip foundation is regulated by SNiP II-B.1-62.
The depth of soil freezing for some Russian cities is shown in the table.
How to calculate the load on a strip shallow foundation
First of all, you should consider:
- structural features of the building;
- building height;
- planned number of floors;
- materials from which the walls will be built;
- coating weight;
Advice.
In general, the entire load can be divided into a constant (calculated before construction begins) and a variable. The latter depends on the number of inhabitants, the weight of the furniture, etc.
- trench depth;
- pillow thickness;
- foundation tape parameters;
- concrete quality.
You can additionally use
Calculation of a shallow strip foundation
1. Depth is determined by the proximity of groundwater and the depth of freezing.
2. Height above ground = 4x width.
Good to know. The height above the ground is less than or equal to the depth.
3. The width is determined by the formula:
Where, D is the width of the base of the foundation;
q is the design load on the foundation, t/m;
R - design soil resistance, t / sq.m. This indicator, for a laying depth of 300 mm, is shown in the table.
4. The thickness of the pillow is determined from the conditions of the strength of the soil of the area.
For heavily heaving soils, the formula is applied:
Where, tn is the cushion thickness;
А, С, W – coefficients;
A and C are determined according to the tables below.
And W = 0.1 or 0.06 sq.m./t for heated and unheated structures.
Above the line - for MZLF with a laying depth of 300 mm, below the line - for non-buried foundations.
Advice.
Make the calculation of MZLF using both formulas and give preference to a larger value.
The cost of a shallow strip foundation
Varies within 4-6 thousand rubles. per running metre. The price depends on the width, height, number of lintels and dimensions, for example, the cost of building the foundation of a 6x6 house will cost 70-80,000 rubles, and 10x10 \u003d 120-150,000 rubles.
Types of shallow strip foundation (shallow)
Depending on the type of MZLF, the technology of its device will differ. Therefore, you should briefly familiarize yourself with the main ones:
Tape monolithic shallow foundation
Poured directly on the construction site, resulting in a seamless tape
Tape block shallow foundation
Blocks are bought ready-made, or they are made separately, and they are only assembled at the construction site. A cement mortar is used as a fixing material.
Each of them has its own advantages and disadvantages. But, in general, the service life of the second is three times less than the first. Therefore, in this article we will dwell in detail on such a form as a monolithic MZLF.
MZLF technology or how to make a shallow strip foundation with your own hands
The instruction is easier to understand if all the work is divided into clear steps. We will not deviate from this scheme. So, the device of the tape shallow foundation is as follows:
Preparatory stage
1. The place where it is planned to pour the foundation is freed from everything superfluous.
Council. Trees that are nearby, uproot along with the roots.
2. All necessary material and tools are delivered to the workplace. Moreover, it is desirable to immediately determine the location of all this stuff, so that later you do not waste time looking for it.
Marking for strip foundation
The importance of this stage is difficult to overestimate. Therefore, you need not only to “estimate” where you will dig a trench, but also to make landmarks with a rope (if possible, a laser level would be better).
How to make markings for the foundation:
- take measurements around the perimeter;
- hammer beacons in the corners;
- check the diagonal between the corners;
- if necessary, move the beacons;
- make a blind area at a distance of at least a meter from the beacons;
- fasten a rope to the blind area boards, which will show the edges of the foundation.
More clearly, the markup process is shown in the diagram.
How to dig a trench under the foundation
A foundation trench is a strip of excavated soil.
The depth of the trench is determined by the depth of the shallow strip foundation and cushion.
For example, the most common depth is 300 mm, the thickness of the cushion is about 200 mm depending on the quality of the soil. Then the depth of the trench will be 500 mm.
Council.
To prevent the edges of the trench from crumbling, make small slopes.
Given the type of soil, it is better to start pouring the foundation immediately. Otherwise, it will crumble, and part of the work will have to be repeated.
The sand cushion under the foundation is a mixture of sand and gravel. They can be mixed, but it is easier to pour in layers. Moisten each layer with water and compact well. Since the structure of the pillow turns out to be quite porous, it is separated from the main foundation with a waterproofing film.
In principle, natural soil can serve as the basis for a shallow-depth strip foundation, but its bearing capacity is much lower than the proposed sand and gravel pad.
Install the entire formwork structure vertically. The supports are fixed in increments of 500-600 mm. They are needed so that under the weight of concrete the formwork does not fall apart and does not warp.
Useful advice.
Try to keep the boards close to each other tightly and without sharp drops. Then you will avoid work on leveling the surface of the finished foundation for cladding.
Filling the strip foundation
Getting concrete is an individual matter - you can buy (or rather, order) and the concrete will be delivered by a mixer or made on your own, and using it (and the second option, how to do it).
As for pouring concrete, the procedure is standard for such work - concrete is poured into the finished formwork.
Council. If the formwork is poured with water, the concrete will lie more evenly along the edges.
When pouring concrete, try to beat it off every 40-50 mm. height. This will "drive out" air bubbles that can destroy the concrete in the future.
Reinforcement of a shallow strip foundation
If a heavy load is not expected on the foundation, this step can be skipped. But still, with MZLF reinforcement it will be much stronger.
Proper reinforcement of a shallow strip foundation:
- Fill in the starting layer. This layer should be about 30% of the total height of the MZLF. The purpose of this action is to create a flat surface for laying the metal, as well as to protect it from moisture.
- Knitting reinforcement for a strip foundation. To do this, you need to tie it into blocks and lay it in a trench.
- Pour concrete to desired height.
An example of a reinforcement cage for a strip foundation
An example of knitting reinforcement with wire. The example shows that the bundle is made with wire. This is a relatively new approach to the connection, because the more familiar one is resistance welding.
But the methods of joining reinforcement by welding have several significant drawbacks, including:
- require a welding machine and a specialist who can perform welding work;
- due to the high temperature of the welding arc, the strength of the hardened rebar is lost;
- welding works are not applicable for fittings with a diameter of more than 20 mm;
- The most important thing is to increase the rigidity of the armored carcass. Since a shallow strip foundation “plays” depending on the season (being a kind of flexible foundation), increased rigidity will lead to its destruction. And as a result, it will be required.
This is what the installed reinforcement will look like
Concrete protection
To avoid overdrying and the formation of cracks, the concrete poured into the formwork is covered with a film and periodically moistened with water.
Insulation of a shallow strip foundation
- Immediately after the foundation has gained the necessary strength, construction of the house should begin. Try to do all the work in one season. Because the soil under the foundation will freeze, and the MZLF, not pressed down by the weight of the house, will deform.
- If you cannot start construction, cover the MZLF and the area near it (200-300 mm) with straw or sawdust. To protect the soil from freezing.
- During the operation of the building, try to plant perennial plants and shrubs near the shallow strip foundation. They will help to reduce the depth of freezing of the soil. And they will also be able to retain a significant amount of snow, which will also reduce the depth of freezing.
Shallow strip foundation video
Conclusion
In this article, we figured out how to make a shallow strip foundation with our own hands. Having dealt with each of the stages in detail, you will be able to prevent unfortunate mistakes and fill the foundation on which your house will stand for more than a decade. Most importantly, do not forget that before starting construction, order geological studies, otherwise, there is a risk that the soil on your site is not intended for the MZLF device.
One of the simplest foundations for buildings is a shallow strip foundation. Despite the ease in the production of work, there is always the possibility of doing something wrong, therefore, before installing the MZFL, you should familiarize yourself with the general technology. Today we will take a step-by-step look at the device of a shallow tape.
Scope of MZLF
Shallow foundations are used for buildings with a low loaded mass. As an example, we can cite houses on a steel or wooden frame, as well as buildings made of lightweight elements (foam concrete, PCB). Usually the number of storeys of buildings on the MZLF does not exceed two.
In the definition of MZLF, shallow - means completely located in the frozen layer of soil, the underground part of the concrete tape rarely exceeds 500-700 mm. The forces of frost heaving with this arrangement do not create tangential (tearing) loads, but the entire building, together with the foundation, dynamically moves following the expansion of the soil. For this and other reasons, it is not recommended to arrange a shallow-depth tape in areas with a general slope of more than 2%. On steeper slopes, a shallow foundation can be built only after the soil has been re-planned to form a horizontal terrace.
The feasibility of using MZLF lies in a much lower consumption of materials and ease of design. If a basement floor is not planned for the building, a shallow-depth tape will reduce the volume of concrete mix and reinforcement by 2-3 times, while providing an equivalent load-bearing capacity.
However, it should be noted that a shallow foundation cannot be established on loose peat, silty soils and mudflow sandy loam. Such soils have too low density and high plasticity, therefore, they require the installation of pile-grillage foundations based on denser soil layers. MZLF should not be arranged on soils with heaving rates of more than 4% or if the GWL is above the depth of occurrence, despite the fact that drainage of the site is not planned, so that after that you do not have to deal with the consequences.
Section and configuration calculation
Since the MZLF acts as a beam, and not a stiffener, usually the section of the tape is close to a rectangle or trapezoid in shape. Tape in the form of a brand or more sophisticated sections is almost never cast due to the fact that the material savings seem too small compared to the installation of more complex formwork.
The calculation of the MZLF is carried out in two directions: sufficient bearing capacity of the soil in the plane of occurrence and its own structural strength, which will allow the tape to maintain rigidity at full design load from walls, roofs, snow, etc.
The width of the upper part of the foundation is determined by the maximum possible wall thickness, taking into account the layer of internal and facade finishing. When installing floors along logs, it may be necessary to form a ledge or expand the foundation by about 50 mm.
The width of the tape in the plane of occurrence is determined entirely by the required bearing capacity. It is enough to divide the total mass of the building and calculate the average load per meter of the perimeter of the tape, and then calculate the sufficient cross-sectional area of the support in accordance with the characteristics of the soil. To create a sufficiently high safety factor, the thickness of the incompressible bedding is not taken into account.
Scheme of a shallow strip foundation: 1 - parent soil; 2 - adding gravel or gravel-sand mixture; 3 - blind area; 4 - foundation reinforcement; 5 - shallow strip foundation with a wide sole for even load distribution; 6 - wall; 7 - gravel bedding of the internal area of \u200b\u200bthe foundation of the house
The height of the tape is defined as a component of its underground and aboveground parts. With the above-ground part, everything is simple - it must be at least 80 mm and not more than four widths of the upper edge of the tape. In turn, the height of the underground part can be determined taking into account several factors:
- the foundation should not lie on the border of heterogeneous soils;
- the minimum depth of the foundation is 35-40 cm, but, depending on the intensity of heaving and the depth of freezing, the height of the underground part can increase by an additional 60-80%;
- to maintain the required strength characteristics of reinforced concrete products, the ratio of width to height should not be less than 3:5.
Earthworks and preparation
The trench profile for the MZLF device should have a width 2.5 times greater than the estimated width of the tape and a depth greater than the height of the underground part by two widths. This is due to the fact that MZLF is rarely arranged along the ground formwork, using a plank-panel board for reasons of containing cement laitance and the need to give the section a trapezoidal shape. Immediately, we note that the indentation of the walls of the pit from the formwork should be twice as large from the outside than from the inside.
Compensation for the forces of frost heaving is carried out due to incompressible, non-porous and hygroscopic filling, as well as filling the side sinuses with similar material. Sand and gravel mixture with coarse sand and granite or basalt crushed stone of fraction 25-30 is used as a backfill material. To stabilize the foundation, the prepared bottom of the trench is covered with a 30-50 mm preparatory layer of M 100 concrete without reinforcement.
Backfilling at the bottom of the trench helps to distribute the load on the supporting soil layer, increase the area of support and involve forces with a horizontal application vector. The recommendation regarding the thickness of the backfill, equal to two values of the thickness of the tape, is rarely followed in practice, more often on weakly heaving soils they are limited to preparation of 25-30 cm.
However, you must remember that the more pronounced heaving, the more responsibility lies with the bedding. Sometimes it is advisable to replace the soil up to the freezing depth and expand the external sinuses to the shape of an inverted wedge, the base of which corresponds to the width of the blind area.
Reinforcement and anchoring
For MZLF, the total content of steel reinforcement without prestressing is set at least 0.1%, a more realistic figure of 0.17-0.2% will provide proper reinforcement without excessive strength, but with a significant margin of safety.
The minimum value of the protective layer for the underground part of the foundation is 60 mm, the maximum is no more than half the width of the tape. The working reinforcement is made with rods with a periodic profile of such a diameter that the total cross section of the reinforcement can be divided into 4 rods for the upper and lower reinforcement lines.
If in the MZLF the vertical distance between the reinforcement lines exceeds 450 mm, another row with rods is added, the thickness of which is at least 60% of the thickness of the main lines.
Structural reinforcement is carried out with clamps or wire for knitting in increments of 2-2.5 values of the average width of the foundation. The diameter of the rods used for the manufacture of structural reinforcement should not be less than 50% of the diameter of the working reinforcement.
In addition, the reinforcement of the MZLF is accompanied by a number of anchorings. At bends and T-shaped joints of the tape, each row of reinforcement in intersecting directions should be connected with bent mortgages of the same section, the overlap of which with the main reinforcement is determined as 25 nominal reinforcement diameters. Anchoring with embedded studs may be required to connect to the base of the frame or masonry walls.
Concrete works
Before carrying out concrete work, it is recommended to cover the inner cavity of the panel formwork with a polyethylene film, which prevents the concrete mass from losing liquid until it sets. After that, the reinforcement segments are installed, they are linked and distanced using plastic plugs.
Most often, bituminous mastics are used to protect against moisture, on top of which fiberglass-based insulation or cheaper roofing material is rolled out. If the foundation does not require continuous waterproofing, the hydrobarrier film remaining after pouring is sufficient.
The sinuses around the foundation fall asleep with ASG immediately after the waterproofing has dried. Backfilling is carried out in layers of 30-40 cm with careful tamping. After that, it remains only to make a blind area around the house, and the MZLF will be ready for further long-term operation.
A shallow strip foundation (MZLF) is a type of strip foundation, which is located 0.3-0.7 m below the zero level. The construction of this type of foundation requires a minimum of financial and labor costs. MZLF is great for light buildings erected on various soils. The foundation has its advantages and disadvantages, as well as a special construction technology.
Shallow strip foundation: scope, pros and cons
The bearing capacity of MZLF, in comparison with bases of another type, is estimated as average and largely depends on the type of soil on the site. A shallow foundation is suitable for the construction of country houses, timber buildings, frame houses, as well as for outbuildings, bathhouses, a barn, etc. A shallow foundation is not suitable for brick houses, large foam concrete cottages and gas blocks. For such buildings, an excellent option would be a combined foundation on piles, for example, a pile-tape shallow type on bored supports.
It is desirable to build a foundation of this type on slightly heaving and non-heaving soils. Ideal - sandy and sandy soils with a low moisture content. The groundwater level should be at least 0.5 m below the depth of laying. Most clay soils are classified as medium and high heaving soils. Features of the construction of the base with a small depth of laying on heaving soils will be considered below.
The advantages of this type of bases include
- profitability, concrete consumption is 30% lower than in the construction of a conventional buried strip foundation or a base with a monolithic floor slab;
- ease of construction, you can build it yourself without the involvement of workers and special equipment;
- a small amount of earthworks - a narrow trench is dug with a depth of no more than 0.7 m;
- small area of contact between the structure and the ground.
Among the shortcomings of the MZLF note
- pouring is carried out at stable temperatures above +10 C;
- limited use due to low bearing capacity
- erection is possible only on a flat surface with a slope of not more than 5 degrees;
- lack of a basement in the house.
Expert opinion
Sergei Fedorov
Ask an expertIf you are planning to build an MZLF base and “freeze” the construction site, then keep in mind that you cannot leave the base unloaded for the winter! When freezing, the soil will push out the monolithic tape, which will lead to a violation of its integrity.
Design features of a shallow foundation
A shallow-depth monolithic-strip foundation is being erected on a flat surface. When building a house on a slope, you will have to combine the MZLF with a pile foundation, using supports to equalize the height difference. In terms of strength and resistance to deformation, the structure must comply with SNiP 2.03.01-84.
In the context of a shallow foundation, it looks like this:
Features of the MZLF, which must be taken into account in the calculation and construction:
- The depth of the foundation sole depends on the depth of soil freezing.
- Be sure to install a pillow of dry bulk materials: a mixture of coarse sand and gravel.
- With a high level of groundwater, drainage is performed under the foundation and around it.
- The base on which the monolithic tape is installed is compacted as much as possible.
- Be sure to equip the blind area to drain rainwater and snow.
Considering these features, we can conclude that the bedding pad and the blind area are an integral part of the shallow foundation. The requirements for the blind area are specified in SNiP 2.02.01–83.
Calculation of a shallow strip foundation
The calculation of the MZLF, which is being built on low and non-rocky soils, is not difficult. During the calculation, three main parameters are determined:
Depth
It is determined on the basis of SN "Foundations and Foundations". The document specifies the following minimum values for the depth of the foundation footing:
- when soil freezing is less than 2 m - 50 cm;
- when the soil freezes to a depth of 3 m - 75 cm;
- when the soil freezes over 3 m - 100 cm.
For most regions of the middle lane, the depth of the MZLF will be 50 cm. For light buildings, such as a frame shed or a small country house, this parameter can be reduced to 30 cm.
Monolithic belt width
In order not to make complex calculations, we recommend taking the width of the sole based on the table:
| Wall and floor materials | Number of floors | MZLF sole width, m |
| Lightweight masonry or aerated concrete walls with reinforced concrete floors | 1 | 0,6 |
| 2 | 0,8 | |
| 3 | 1,2 | |
| Timber framed walls with timber joists | 1 | 0,4 |
| 2 | 0,4 | |
| 3 | 0,6 | |
| Log walls with wooden floors | 1 | 0,3 |
| 2 | 0,4 | |
| 3 | 0,6 | |
| Timber-framed walls | 1 | 0,2 |
| 2 | 0,3 | |
| 3 | 0,4 |
Height above ground level
The higher the monolithic tape rises above ground level, the better the floors of the house will be protected from dampness and cold. However, the height of the foundation to maintain stability and bearing capacity must be correlated with its width. The best option: the height of the tape above the zero mark is equal to its width.
Expert opinion
Sergei Fedorov
Professional builder. Experience 18 years
Ask an expertExample: The laying depth is 50 cm. The width of the monolithic tape according to the table is 30 cm. This means that the height above ground level will be 30 cm, and the height of the entire monolithic tape will be 80 cm. The height of the ground part of the MZLF should not be lower than the snow level. The value of snow height depends on the region (it can be found on the Web). For the regions of the middle zone, this value does not exceed 8-10 cm.
Calculation of MZLF on heaving soils
When building a house on heaving soils, more complex calculations are made, the purpose of which is to determine the heaving deformation. It is quite difficult to make such a calculation on your own, so you need to entrust it to professional designers or use a ready-made table:
| Name and degree of heaving of soils | Number of floors of the building | Foundation footing width b, m | Pillow thickness t, m | Foundation design option | Reinforcement option |
| clays, loams and sandy loams, sands are fine and silty wet - medium sandy | 1 | 0,3 / 0,2 | 0,6/0,7 | G. | 3 |
| 2 | 0,3 / 0,2 | 0,5 / 0,6 | G. | 3 | |
| 3 | 0,3 / 0,2 | 0,4 / 0,5 | G. | 3 | |
| clays, loams and sandy loams, sands are fine and silty wet - strongly heaving | 1 | 0,3 / 0,2 | 0,7 / 0,8 | G. | 4 |
| 2 | 0,3 / 0,2 | 0,6 / 0,7 | G. | 4 | |
| 3 | 0,3 / 0,2 | 0,5 / 0,6 | G. | 4 |
In column 2 "Width of the sole" and column 3 "Cushion thickness" through the / sign, the values \u200b\u200bare indicated for heated and unheated rooms. The column "Reinforcement option" indicates the minimum number of reinforcing bars that must be used to reinforce the monolithic tape.
Shallow foundation device: construction technology
The technology for erecting MZLF is not complicated, pouring can be carried out according to SNiPs 3.03.01-87, 2.02.01-83 or according to our instructions. The base for a frame house 10 x 10 m can be poured in 1-2 days. Before you start pouring, you need to decide where you will take the concrete solution. There are two options:
- 1order concrete class B22.5 ... B17.5 at the nearest RBU. In this case, the mixture will be delivered to you at the specified time by a concrete mixer truck. If the ABS cannot drive up to the place of pouring, then a special sleeve is used, through which the concrete solution will be supplied to the formwork. Ordering a sleeve will slightly increase the cost of ABS services. In addition, you will have to pay for every hour of downtime of the special vehicle.
- 2 prepare the concrete yourself. At the same time, you will not depend on RBU and spend much less money, however, the quality of the concrete mix will be slightly lower. When mixing concrete, the recipe must be strictly observed. To prevent the concrete from setting ahead of time, special additives can be used. Concrete can be prepared immediately after formwork has been installed.
Installation of MZLF: step by step instructions from A to Z
Preparatory work and markup
The device of a shallow foundation begins with the preparation of the site, which consists in removing debris and uprooting stumps. The top layer of soil with vegetation is cut off. If necessary, leveling and backfilling of the soil is carried out, followed by tamping.
The markup is carried out as follows: the perimeter of the future foundation is established, beacon pegs are hammered in the corners. Ropes are pulled along the future monolithic tape.
Expert opinion
Sergei Fedorov
Professional builder. Experience 18 years
Ask an expertThe diagonal between the corners should be strictly 45 degrees. You can check the evenness of the markup using a tape measure and a building level.
Trench and cushion device
The depth of the trench depends on the depth of the foundation and the thickness of the pillow. In width, the trench is made 10 cm wider than the calculated thickness of the monolithic tape. This is necessary for the installation of formwork. During the construction of the MZLF on loose soils, it is possible to strengthen the slopes of the trench with boards. Pillow filling is necessary to reduce the impact of frost heaving forces on the foundation. The thickness of the cushion, as a rule, is 20-30 cm for weakly heaving and non-heaving soils. For heaving - is determined by the table, which is given above.
For the corners where the walls of the future house intersect, it is necessary to strengthen the reinforcing cage by installing additional vertical rods that are welded to the longitudinal rods. Such reinforcement allows the strip foundation to withstand the critical loads acting at the intersections of the walls.
It is possible to lay the armoframe on a prepared pillow, but it is better to do this on the starting layer of concrete. The thickness of the starting fill should not exceed 20% of the entire height of the tape. Concrete pouring helps to create a more even surface on which the reinforcement cage is laid. If you decide not to fill in the starting layer, then to raise the reinforcement cage above the surface of the pillow by 5-7 cm, you should use supporting fungi.
Expert opinion
Sergei Fedorov
Professional builder. Experience 18 years
Ask an expertArmoframe should be located in space, nowhere in contact with the backfill and formwork.
Pouring concrete
Filling should be carried out at a temperature of +10 C and above. Before pouring, the formwork must be moistened, then the concrete will lie more evenly. It is necessary to pour the mixture in layers, the layer thickness should not exceed 40 cm, optimally - 20-30 cm. Each layer is subjected to 5-10 minutes of vibration compaction. This technology does not allow the formation of voids inside the concrete. To supply the concrete mixture to the formwork, it is necessary to use an elastic sleeve or chute.
Layered pouring of the foundation
After pouring, the formwork is covered with a vapor-tight film. The hardening of concrete lasts 25-30 days, after which the formwork is disassembled, and the sinuses between the foundation and the trenches are covered with soil.
Insulation of a shallow foundation
Professional builders recommend that you definitely insulate the MZLF. It is recommended to do this immediately at the time of construction of the structure. An insulated foundation will protect the floors of the house from dampness and cold, which is especially important when arranging the floor “on the ground”. In this case, in the absence of thermal insulation, all the heat from the floor will go into the ground.
There are external and internal thermal insulation MZLF. External - when the insulation is attached to the outside of the monolithic tape, internal - from the inside. External insulation is considered mandatory, and internal insulation is usually done if the house is with a cellar basement. What heater to use? There are a lot of options. The most popular are:
- Penoplex. A dense thermal insulator that perfectly saves heat. Its service life is much longer than that of conventional foam. Penoplex is resistant to rodents, mold and practically does not absorb moisture. In terms of price / quality ratio, this is the best material for thermal insulation of a shallow base.
- Styrofoam. The extruded material is slightly inferior to foam plastic in terms of physical and mechanical properties. However, the price of expanded polystyrene boards is 20-30% cheaper. It can be used in dry and dusty soils with minimal moisture.
- Polyurethane foam. Liquid sprayed thermal insulation is an expensive option, but at the same time it has many advantages: no joints between the plates, a service life of at least 50 years, minimal water absorption and resistance to aggressive environments.
It is not recommended to make a prefabricated foundation on heaving soils. The forces of frost heaving will push out individual elements, which will lead to the destruction of the foundation.
With the correct implementation of all work on the installation of the FBS, the prefabricated foundation of a small foundation will last 70-80 years. It is this operational resource that reinforced concrete blocks have.
Among all the options for building a foundation, shallow enjoys particular popularity.
It allows save on earthworks and required materials, provide a reliable basis for the future structure and, which may be especially attractive, to complete all the work on one's own.
What you need to know and how to deal with this task, we will tell.
What is a shallow foundation?
The name itself already quite accurately defines the features of this type of foundation: it buried into the ground, but finely, not deep. But seriously, on average, the depth of such a foundation is 50 cm, Oh really not deep, and quite capable on one's own dig a trench without involving labor and equipment from outside.
It is a concrete reinforced tape, on which subsequently erected outdoor And internal bearing walls. Best conditions for using a shallow foundation - non-foamy soils and low-rise structure made of non-heavy materials, which include:
- , frame-panel structures;
- Cellular concrete - expanded clay blocks, foam concrete etc.;
- Lightweight brickwork.
Considering that in most cases such a foundation is located above the level of soil freezing, it is necessary to take into account the soil and ensure styling matching pillow. You can read more about this in dedicated to technology. devices such pillows under the foundation.
Device
The shallow foundation is quite simple by design. On the sandy(sand and gravel) cushion concrete is poured into the formwork of the desired configuration and size. Its necessary strengthen fittings.
cured coating waterproofed. The depth of occurrence depends on the weight of the structure, the characteristics of the soil. The height of the foundation above the ground should not to be more height of the underground part of the foundation.
The possibility of using such a foundation can be limited the complexity of the terrain (construction on a slope), as well as the ground. Use on sapropelic and peat soils of a shallow foundation ruled out.
How to make a calculation?
To calculate the parameters of a shallow foundation, you need to know several soil parameters and future construction, including level groundwater flow, depth soil freezing, calculated weight buildings, snow, calculated resistance soil, etc. In general terms, we will describe the calculation technology.
Initial data
For the initial data, we will take a one-story house by measurement 10x8 m with walls made of aerated concrete with block sizes 600x300x200mm and one internal load-bearing wall. The density of this material is approx. 500 kg/m³. Rough calculation, taking into account door and window openings, as well as one load-bearing internal wall, will show that the weight of the walls can be 15 t.
Similarly, one can calculate weight attic floor, gender, roofing, snowy loads(for example, for the Moscow region it is 160 kg/m2). This needs to be added weight insulation materials, facing brick(if it will be used), metal for doorways, etc.
And don't forget about useful load, which consists of people, furniture, equipment, dogs, cats, cages with budgerigars, etc. In order not to catch your Barsik for the purpose of weighing, the payload value is assumed to be 180 kg / m2. This value is somewhat redundant, but allows to take into account all possible loads inside the premises.
Payment
Suppose that the final value of the weight of the house turned out to be 130 tons. Now let's define the calculated pressure on the ground, for which we will divide weight buildings on the area of the base of the foundation. Let us assume that the planned foundation will be width 35 cm. Then the area of its base will be approximately 15.4 m². 130 divided by 15.4 and we get that estimated the specific pressure on the ground is 8.44 t/m².
Next, this value is compare with calculated soil resistance. For example, for alumina this value is 10 t/m². This means that the previously selected size of the foundation provide that the soil will support the building.
Given that width foundation should be more wall width approx. 10 cm, you may need to increase the width of the base of the house. This will lead to an increase masses foundation and will need to be done recalculation, but even a slight increase in the width of the foundation will provide stock by ground load.
Construction technology
After everything is calculated, it's time to start working on laying foundation. It can be divided into several stages.
markup
According to plan marked out territory for the future building, with the help of pegs and a stretched rope, the perimeter of the work is determined.
Advice! It is desirable to remove the top fertile layer of soil over the entire area.
Trench
dug out trench desired depth. It is necessary not to forget to take into account not only the dimensions of the foundation, but also the pillows under it. Width trenches should be more the width of the base of the house so that nothing interferes with the formwork.
After all the soil is taken out, it begins styling pillows.
At first recommended lay geotextile, which will prevent mixing sand with soil. Sand, pre-moistened, is laid in layers on 15-20 cm and carefully rammed down using vibrating plates.
After the formation of the pillow is completed, you can proceed to installation formwork.
How to make a waterproofing strip foundation with your own hands:
formwork
Most commonly produced from boards, but you can buy it at a hardware store, made metal or plastic. When installing formwork necessary keep a close eye on verticality walls and holding permanent distances between them. For strengthening, pegs, bars are used, spacers are nailed on top, which will help later keep poured cement mortar.
Formwork walls can be pull off wire. The inner walls of the boards should be smooth. Steel, asbestos-cement or other pipes should be installed in advance for ensure underground ventilation.
They are installed perpendicular formwork and covered with sand, which prevents concrete from getting into them and deformation when pouring the foundation.
Reinforcement
After completion formwork installation before starting to pour concrete, necessary provide for it. In the case of the construction of light buildings, reinforcement can be neglect, in other cases, perform it extremely recommended.
Used rebar diameter 10-16 mm, which is located longitudinally along the entire length of the foundation. Usually, in the lower and upper parts of the future foundation of the house, two reinforcement bars are laid, retreating from the edges by several, recommended by 5 centimeters. transversely steel bars with a diameter 6-8 mm. They are connected to each other with a wire.
For reinforcement enough arrange 2 reinforcement belts, but for a large foundation height and heavy loads, the number of belts can be increase.
Beyond the need use welding equipment, with this method of connection, due to heating, the structure of the metal and its mechanical characteristics change. increased rigidity at the welding site can become reason for the gap during pouring with concrete, or may subsequently create internal stresses in the foundation, preventing it from responding to temperature fluctuations.
pouring concrete
Concrete grades are often used for foundations. M200. The finished mixture is poured in layers approximately 15-20 cm.
Attention! Preferably every layer tamp down using a vibrator or rammer, or at least a piece of rebar pierce surface to remove possible air pockets.
The next layer must be poured before solidification the previous one. After graduation concreting, the foundation is needed shelter film and leave to harden, from time to time wetting water.
Pre-hardening will take place in 3-4 days, then it will be possible dismantle formwork. For further work, the concrete will be suitable through 2-3 weeks.
Blind area what is it?
protects foundation from soil erosion by melt water, precipitation, diverting unwanted moisture from the base of the house. In addition, it can also serve path around the house.
Her device not difficult. It consists of two parts:
- Foundations. To do this, a layer of sand is laid, or several layers of gravel and sand.
- decorative coating. In the simplest case, this is a layer of concrete, but you can use stone, pour asphalt, fill with gravel.
The slope of the blind area away from the house should be at least 1.5˚. Optimal if the height difference between the edges is 8-10 mm.
Between the wall and the blind area you need to leave expansion joint order width 2 cm. Roofing material, expanded polystyrene is laid in it, sand or other waterproofing material.
The width of the blind area should be not less the width of the eaves of the house so that the water rolling down from the roof gets on her and not on the ground. In addition, another point can affect the dimensions - the insulation of the foundation.
Why is base insulation necessary?
After the foundation concrete has completely hardened, it must be covered several layers of bituminous mastic and shelter waterproofing material, for example, roofing material. Next step - . Reinforcement laid in concrete conducts cold well, and insulation measures will reduce this unfortunate effect.
In addition to actually improving the temperature indicators of the structure, there is another important moment.
Soil heaving
Considering the shallow depth of the foundation, above freezing boundaries, it is affected by vertical and tangential forces of frozen soil. This compensated cushion under the foundation, and lateral forces can be compensated by laying insulation under the pavement.
A good option would be to use extrusion polystyrene foam, which is buried to a shallow depth under decorative pavement coverage. Knowing depth soil freezing (recall, for the Moscow region it is about 1.4 m), if the width of the laid insulation, and, in fact, the blind area, will be not less this value, the soil at the point of contact with the foundation will not freeze.
IN video below is shown in detail device finely ruined strip foundation:
- Date: 23-07-2015
- Views: 2091
- Comments:
- Rating: 20
How is a shallow base on a tape made?
The method of laying the foundation on layers of soil that are below the freezing depth may be suitable for the construction of brick or stone buildings that have 2 or 3 floors. The bearing capacity of a deep foundation in the construction of light houses is used by only 15-20%. It follows from this that 90% of materials for construction are spent unproductively.
A shallow strip foundation will cost 2-3 times cheaper than a buried version of the foundation.
For summer houses and low-rise buildings of lightweight construction, it is advisable to use a shallow monolithic strip foundation, which is laid directly into the freezing ground layers, but 50-70 cm above the groundwater level.
Elements that you will need for this type of do-it-yourself:
- cement;
- crushed stone or gravel;
- water;
- sand;
- reinforcement bars;
- brick;
- excavator;
- spacers and stakes;
- wooden bars;
- ruberoid;
- fiberglass, agril or polypropylene foam;
- boards that are planed on one side;
- geotextile;
- tamper;
- building level.
Advantages of a strip shallow foundation
Such a base is a reinforced concrete tape that will need to be laid under all the walls of a private house. The foundation of this type is used for soils that do not belong to the category of strongly swelling. In such soils, groundwater should be located low. On such a foundation, it is recommended to build only light private houses and other structures.
Crushed stone or gravel can be compacted if it goes in layers along with river sand.
After digging the trench, you will need to drill 2 wells with a distance of 2-3 m between them. Their minimum depth is equal to the depth of soil freezing. The maximum depth is not limited in this case. A pipe must be inserted inside the well, which is then covered with crushed stone. The bottom of the trench under the base is covered with rubble, the areas around the pipes are covered with sand, which will need to be carefully compacted. Gravel should be poured on top of it. Next, formwork panels and reinforcement are installed. At the end, the concrete mixture is poured.
A trench is laid outside the strip foundation. Its depth should reach the crushed stone layer of the foundation trench. Next, the trench is again covered with rubble, and a blind area is arranged on top, the width of which is 50-100 cm. Instead of a pipe, it is possible to use a non-rotting non-woven material. In this case, fiberglass, agril and polypropylene foam can work well.
Allows you to divert rain and melt water into crushed stone, and then into the pipes of the drainage system. The foundation will always be in the backfill of dry rubble. During frost, dry soil will not be heaving.
The need for waterproofing a shallow strip foundation and its main types
One of the main conditions for the possibility of using the foundation for a long time is the device of reliable waterproofing.
Such protection of the foundation of a private house can be performed in the following ways:
coating waterproofing. This method is the least expensive and least durable. This is due to the vulnerability to mechanical damage. The surface of the strip foundation when applying the waterproof layer must be completely dry;
Coating insulation can be used if it is planned to produce in the future, protecting it with brickwork or geotextiles.
In most cases, roofing material is used for waterproofing. It is laid on a hot mastic previously applied to the base. The overlap with a double layer of roofing material should be 15-20 cm.
Sprayed waterproofing must be applied with a special spray gun. Strip foundation before processing by pollination will need to be cleaned of dust.
Recently, they are widely used in suburban construction. Especially often they are erected by developers who are engaged in construction on their own.
More about reinforcement of this type of shallow foundation
Reinforcement of a shallow strip foundation is carried out to enhance the strength of the concrete structure. In this case, this is the assembly of the foundation skeleton, which will act as a protection for the foundation slab from negative environmental influences.
As a material for reinforcement, it is necessary to take reinforcement with a diameter of 15-16 mm, as mentioned earlier. In this case, there is a nuance. According to building codes, the reinforcing lattice can be made of reinforcement with a cross section of 14 mm or more, but it is planned to put a light structure on the foundation, therefore reinforcement with a cross section of 10 mm may be sufficient.
The grid cells will look something like this:
- length - 0.5 m;
- width - 0.3 m;
- height - 0.75 m.
This length is recommended by experienced builders. The cell width is determined based on the fact that the reinforcement should be inside the concrete 5 cm from the edge of the structure. The thickness of the foundation slab is 0.4 m, so the cell width is 0.3 m.
The height is calculated based on the fact that the total height of the foundation slab is 0.8 m. In this case, pieces of brick may come in handy. The height of the pieces of this brick should be approximately 5 cm, so the indent from the upper border will also be 5 cm.
The fittings are welded by a welding machine at the joints. If there is no such apparatus, it is possible to fasten the reinforcement with knitting wire. There is an opinion that the frame, when tied with wire, acquires spring properties, which can positively affect the durability of the foundation as a whole.
Calculation of the cost of reinforcing a shallow foundation of this type
First of all, you need to find the length of each of the sides and jumpers of the base from edge to edge. Next, subtract 10 cm from each length. The foundation is made shallow, therefore there is only one cell in depth. The resulting length should be multiplied by 4 (2 strips from the bottom and top). It will turn out the footage of the reinforcement, which will need to be laid around the entire perimeter.
Next, the found total lengths of each side are added up. The resulting figure is divided by 0.5 m. All this is multiplied by the thickness of the foundation minus 0.1 m. At the end, the resulting value must be multiplied by 2. This will turn out the footage of reinforcing bars for the crossbars.
Further, the number of cells in the perimeter, which was found earlier, is multiplied by the height of the monolith minus 0.1 m. All this is multiplied by 2. Thus, you can find the footage of the reinforcement from which the cells will be reinforced in depth.
All the resulting numbers will need to be added to get the total footage of the reinforcement bars that are necessary to complete the reinforcement of the foundation. It is recommended to buy rods with a margin.
When buying reinforcement, it is ideal to order also its cutting. The average cost of cutting is 2.5 rubles per cut.
Do-it-yourself features of a strip foundation for shallow laying
- In the process of constructing a sand cushion, sand must be poured in small layers of 18-20 cm. If the soil available on the site passes moisture well, you will need to pour water between the layers of sand and compact it all well.
- A shallow foundation should not be left unloaded for the winter. If it is not possible to complete construction before the onset of cold, you will need to create a special temporary layer of thermal insulation around the entire monolithic foundation. To perform this work, it is recommended to use sawdust, expanded clay, straw, slag and other materials that can somehow provide protection from frost.
- Waterproofing material must be laid tightly, but without a strong fit. If there is waterproofing of a liquid consistency, the coating will need to be done in 2 layers (thin and thick).
- It is forbidden to start building a foundation on frozen ground. It is allowed to build this structure only after the withdrawal of groundwater and complete thawing of the soil.
- If a private house, which is being built on a similar foundation, will have a basement, its size must be limited.
- In order to be able to increase the rigidity of the base of the walls and the walls themselves, it is necessary to use additional reinforcement. In this case, the soil will not subside under the middle of the structure, because the internal walls, which are reinforced with a strong reinforcing belt, will take the blow.
guarantees an improvement in the strength characteristics of the walls.
It is quite simple to arrange a strip foundation on piles or another type. To do this, you will need to purchase all the necessary materials and tools, as well as strictly follow the manufacturing technology of such a design.
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