The foundation is an important supporting structure of the building, the quality of which determines its durability and safety of operation. Depending on the features of the house and the characteristics of the base under it, they choose from several types of structures, each of which requires calculation and competent design. The strip foundation is one of the most commonly used for private construction. When it is constructed, different technologies are used, one of which is reinforcement.
Strip foundation reinforcement is used for both prefabricated and monolithic structures. If, when using foundation blocks produced at the factory, it is not possible to adjust the percentage of reinforcement and the diameters of the rods, then in monolithic structures, the process of selecting reinforcement and placing it in the thickness of the tape plays an important role. Why is reinforcement needed and how is it carried out?
Why and when is it necessary to reinforce strip foundations
A feature of concretes, which are used in the production of many types of foundations, is that they do not respond equally to different types of loads. Compressive, tensile, twisting, bending forces act on each building element of a building to a different extent. Concrete reacts differently to them. For example, if it can withstand a compressive load of a certain value without problems, then the same tensile force can lead to cracking and destruction of the material.
Reinforcement is used to solve the problem. It consists in the fact that steel rods are installed in tension zones, which are connected to concrete in one structure and perceive tensile loads. When calculating, it must be borne in mind that stretching is possible in different parts of the foundation, depending on the acting forces. There are also conditions that in one zone there are first compressive, and then (during heaving or subsidence) tensile forces.
To reinforce a monolithic strip foundation, rolled steel rods are used. The fittings are divided into classes, depending on the features (A-I, A-II, A-III). Directly in the thickness of concrete apply:
- separate rods;
- reinforcing meshes;
- reinforcing frames.
Grid - a flat structure of longitudinal and transverse rods interconnected. Frame - a three-dimensional element, which is the same longitudinal and transverse rods connected into a three-dimensional structure. The choice of the type of reinforcement scheme for the strip foundation is justified during the design, depending on the value of the loads and the features of the foundation.
Necessary materials
For reinforcement, rods made of rolled steel of several classes are used. For strip foundations, the following are most often used:
- A-III with a diameter of 10-16 mm as a working one, which perceives tensile loads;
- Vr-1 with a diameter of 4-5 mm for transverse reinforcement (smooth wire).
A knitting wire is also needed, with the help of which the rods are connected to each other into a single frame or mesh. Knitting occurs with the use of a special hook, which is made from a steel rod or purchased at hardware stores.
To increase the service life of the reinforcement and protect it from atmospheric action, it is necessary to provide a distance from the outer surface of the concrete to the edge of the rod. This distance is called the protective layer. For the foundations of private houses, it is at least 30 mm.
Various methods are used to provide a protective layer. Basically, this is the laying of supports made of different materials. To do this, use trimmings of reinforcement, pieces of steel, or purchase special coasters in hardware stores.
Reinforcement scheme for buried foundations
Reinforcement of a buried strip foundation is carried out with longitudinal reinforcement bars connected into a frame. Where are the working rods located? Since they perceive tensile forces, they are placed in zones of such loads. In a strip foundation, this is the upper and lower part of the structure. At the same time, tensile forces do not occur in these two parts of the foundation, but when designing it is not always possible to determine with a high probability that the load will occur only in the upper or only in the lower zone.
The foundation works like a beam, which is affected by the weight of the building and possible heaving forces. If the design is calculated and built correctly, then the house evenly presses on the entire tape. In this case, tensile forces may not arise. But if there is a drawdown, or heaving, then the loads increase unevenly. For this, reinforcement is carried out.
The frame is positioned in such a way that the working reinforcement is protected by a layer of concrete. For it, rods of brand A-III are used. The diameter is selected by calculation, but more often it is 12-14 mm. The transverse rods are made of wire Vr-1 4-5 mm in increments of 150-200 mm.
In the cross section, two working rods are more often placed in the lower and upper zones, but with a large width of the tape, three can also be used. This option is possible if the tape width is from 400 mm and above.
The corners of the foundation, as well as the joints of the walls, are reinforced with reinforcing diagonal rods, the edges of which are turned around and hooked to the frame or stack on each side.
Since fittings are often sold in lengths of 6 or 12 mm, it is important to calculate the dimensions before purchasing so that they are cut into the required lengths directly upon purchase.
Reinforcement scheme for shallow foundations
The difference between shallow foundations is that their sole is not located below the depth of seasonal freezing of the soil. The principles of reinforcement and work technology are the same as for buried ones. There are options and location of the tape directly on the upper surface of the soil. The lack of deepening leads to the fact that it is especially necessary to take into account the effect of heaving forces in the winter period.
Basically, the reinforcement of shallow strip foundations is carried out with grids. Their location depends on the degree of heaving of the soil. On non-rocky and weakly rocky soils, reinforcement is not always used. This makes the design cheaper.
Grids consist of longitudinal reinforcement bars of class A-III of different diameters. For small buildings, rods with a diameter of 10 mm are more often used. In the cross section of the tape, two rods are more often placed at the top and bottom of the foundation. For transverse reinforcement, wire Vr-1 with a diameter of 4 mm is used.
Reinforcement of the corners of a strip foundation of this type is carried out by the same methods as for a deep foundation - by the device of reinforcing rods of the corner joint. Also, the joints of the walls need to be strengthened.
Stages of work
Let us consider in more detail the stages of work for reinforcing the strip foundation with our own hands. Before starting work, it is important to correctly calculate the amount of reinforcement and choose a scheme. You can also use standard solutions, but there is always a possibility that the characteristics of the soil in your area require the use of special measures to strengthen the foundation and the proposed average frame parameters are not suitable for strength characteristics.
Another option is also possible, when the base is strong and does not require the use of such an amount of material as is proposed for use. There is an overspending and appreciation of the house. To avoid these troubles, it is recommended to carry out a professional calculation of the structure with the involvement of a civil engineer.
If the scheme is developed and materials are purchased, proceed with the installation. Work is carried out in the following order:
- It is necessary to mark the dimensions of the foundation on the surface of the soil. It is important to observe the dimensions and angles exactly.
- Mark out trenches. Their width should be such that it is convenient to assemble the formwork. More often, a margin of 15-20 cm on each side is enough for this.
- Dig trenches for belts. The depth of the trench consists of the height of the foundation and the sand bed. The thickness of the sand cushion depends on the heaving of the soil. In low-heaving clay soils, 10 cm is enough, and in heavily-heavy clay soils, 60 cm of backfill is also arranged. It is better to choose the exact value of the layer thickness by calculation or according to tables in the regulatory literature. Buried foundations are located below the freezing depth of the soil in the region.
- Install formwork. For her apply wooden planks or sheet materials (OSB, steel). The most commonly used boards conifers 25-40 mm thick. The height of the formwork should be 5-10 cm higher than the top of the tape itself. Before installation, the boards are knocked into shields of the desired width. The shields are successively installed in the trench and fixed.
- Prepare fittings. If meshes are used, then vertical rods from reinforcement scraps are driven in for them in the prepared formwork. A distance of 50-100 mm is arranged between them. The distance from the pins to the formwork is chosen in such a way as to provide a protective layer of reinforcement (from 30 mm). The frames are knitted either directly in the formwork, or outside it, and then transferred.
- The reinforcement bars are knitted together with a special wire using a hook.
- The corners and intersections of the walls are reinforced with additional rods.
- After creating the frames or fixing the grids in the formwork, their reliability is checked and the foundation is concreted.
The construction of walls can begin after reaching the required strength. This period depends on the quality of the concrete mixture and the ambient temperature. On average, the design strength of concrete is achieved in 28 days.
Reinforcement of the sole of the strip foundation, if any, is carried out with a reinforcing mesh, into which it is connected to the frame of the strip itself before concreting.
The foundation is the main component of any structure, as it acts as its supporting structure, on which the durability and safety of operation depend. Lately for building frame houses, cottages and household facilities choose the installation of a shallow strip foundation.
It is ideal for all types of soil, is characterized by high strength, and its laying can be easily done by hand.
Peculiarities
Shallow strip foundation is one of the modern types of foundations that are used in the construction of both one-story and two-story buildings made of foam block, expanded clay and wood. According to the requirements of SNiP, such foundations are not recommended for erecting buildings with a height of more than 2 floors that exceed an area of 100 m2.
Such structures are considered a good option for buildings on clay, but during their design, the size of the structure must be taken into account. GOST also allows shallow strip foundations for unstable soil. Thanks to their design features they can move along with the soil, protecting the building from possible shrinkage and destruction, in this they are inferior to the columnar foundation.
To make the foundation reliable and durable, it is installed on bored piles and monolithic reinforced concrete slabs are laid, which are deepened into the soil by 40-60 cm. First, the site is carefully leveled, then formwork is laid out around the entire perimeter, the bottom is covered with sand and reinforcement is laid. For such a foundation, as a rule, a monolithic slab is made with a thickness of 15 to 35 cm, its dimensions depend on the dimensions of the future structure.
In addition, a shallow strip foundation has some features that must be considered during its construction:
- the base is buried no deeper than 40 cm, and its width is made 10 cm more than the thickness of the walls;
- on heaving soil, it is imperative to create monolithic reinforced concrete structures, which will help reduce the load from above and balance the heaving forces from below;
- laying should be carried out on well-prepared and pre-compacted soil;
- at high level ground water it is necessary to provide for laying high-quality waterproofing and installation of a drainage system;
- a shallow foundation requires insulation from above, since the thermal insulation layer will protect the base from temperature changes and serve as an excellent source of heat.
Advantages and disadvantages
Today, during the construction of buildings, you can choose any type of foundation, but a non-buried strip foundation is especially popular with developers, as it is considered the most reliable and has positive reviews when operating structures on heaving soils and on clay. It is also often installed on a site with a slope, where a recessed version of the design cannot be performed. Several characteristics are considered the main advantages of such a foundation.
- The simplicity of the device. Possessing even minimal skills, it is quite possible to lay the structure with your own hands without involving lifting mechanisms and special equipment. Its construction, as a rule, takes several days.
- Durability. Observing all technologies and construction standards, the foundation will last more than 100 years. In this case, special attention should be paid to the choice of brand of concrete and reinforcement.
- Possibility to design houses with basement and basement. With such a layout, the reinforced concrete tape will simultaneously serve as a supporting structure and walls for the basement.
- Minimum cost of building material. For work, you only need reinforcement, concrete and ready-made wooden panels for the manufacture of formwork.
As for the shortcomings, some features can be attributed to them.
- Labor intensity. For construction, it is necessary to first carry out earthworks, then make a reinforced mesh and pour everything with concrete. Therefore, in order to speed up the installation process, it is advisable to use the help of wizards, but this will entail additional costs.
- Easy to build. In the case when laying is carried out in winter, concrete acquires its strength later, after 28 days. And this means that you will have to wait a month, since the base cannot be loaded.
- The inability to construct tall and large buildings. Such a foundation is also not suitable for houses, the construction of which is planned from heavy material.
- The need for additional styling waterproofing.
Calculation
Before you start laying the foundation, you need to design and make accurate calculations. The complexity of the calculations for shallow strip base is to determine the hydrogeological characteristics of the soil on the site. Such studies are mandatory, since not only the depth of the foundation will depend on them, but the height and width of the slabs will also be determined.
In addition, in order to make correct calculations, you need to know the main indicators.
- The material from which the construction of the building is planned. The strip foundation is suitable for both aerated concrete houses and buildings made of foam blocks or timber, but it will differ in its device. This is due to the different weight of the structure and its load on the base.
- Dimensions and area of the sole. The future base must fully comply with the dimensions of the waterproofing material.
- The area of the outer and lateral surface.
- The dimensions of the diameter of the longitudinal reinforcement.
- Mark and volume of concrete solution. The mass of concrete will depend on the average density of the solution.
In order to calculate the laying depth, it is first necessary to determine the bearing capacity of the soil at the construction site and the parameters of the sole of the tape, which can be monolithic or consist of blocks. Then you should calculate the total load on the foundation, taking into account the weight of the ceilings, door structures and finishing material.
It is also important to investigate the depth of soil freezing. If it is from 1 to 1.5 m, then the laying is carried out at a depth of at least 0.75 m, when freezing to more than 2.5 m, the base is buried to a depth exceeding 1 m.
materials
Installing the foundation for the building involves the use of high-quality building materials, is no exception to this and a shallow strip foundation. It is erected from a reinforced concrete frame on a sand cushion, while the layout can be either monolithic or consist of blocks.
Steel bars are used to reinforce the base, which, depending on their characteristics, are divided into classes A-I, A-II, A-III. In addition to rods, reinforcing cages, rods and meshes are also laid in the thickness of concrete. The mesh and frame is a structure made of transverse and longitudinal rods that are attached to each other.
The reinforcement scheme is chosen in accordance with the design features, and it depends on the loads on the foundation. For the installation of a shallow base, steel bars with a diameter of 10 to 16 mm are well suited, they withstand loads and stretch well. Transverse reinforcement, as a rule, is performed using a smooth wire with a diameter of 4-5 mm.
Knitting wire is also used as an auxiliary material; it fixes the rods in the manufacture of the mesh and frame.
To increase the life of the foundation, all reinforcement elements must be protected from external factors; for this, a gap of 30 mm is left between the edges of the rods and concrete.
In addition to the protective layer, the reinforcement is additionally placed on the supports, so both special stands sold in stores and pieces of steel or metal scraps can be useful for construction. During the laying of the foundation, the manufacture of formwork is provided, it can be purchased both in finished form and independently knocked down from wooden boards.
Medium-sized sand is used to backfill the air cushion, and the filling is carried out with a concrete solution of different grades. At the same time, concreting is best done with a high-class solution, brand M100 and higher.
Device steps
The technology of installing a shallow foundation is not particularly difficult, so it is quite possible to do all the work yourself. Before starting laying the foundation, you need to draw up a project, as well as an action plan, in which all the activities “from A to Z” should be written. In order for the foundation to reliably serve for more than a dozen years, it is important to pay attention to such points as insulation, waterproofing and the frequency of reinforcement fastening.
It is best if the foundation is monolithic.
It is also important to first make a geodetic assessment of the soil, which will determine the level of groundwater, soil composition and freezing depth. The choice of the type of foundation and the depth of its bookmark will depend on these parameters. In the event that it is planned a budget option construction, it is enough just to drill several pits in different places of the site and independently study the soil.
The soil, in which there is an admixture of clay, easily rolls into a ball, but if it cracks during formation, then the soil consists of loam. Sandy soil cannot be rolled into a ball, as it will crumble in your hands.
After the composition of the soil is determined, you can proceed to the construction of the foundation. Usually, step-by-step instruction provides for the following steps:
- calculation of the reinforcement section, tape width and drawing up a reinforcement scheme;
- making a pit for ground floor or trenches for buildings without a basement;
- laying the drainage system and thermal insulation;
- installation of formwork and fastening of reinforcement;
- pouring with concrete mortar and installation of waterproofing after demoulding.
The completion of laying the foundation is considered to be the insulation of the blind area, for this it is lined with a special material that is resistant to moisture. If all the instructions are followed correctly, in compliance with the technologies and construction standards, then the resulting shallow strip foundation will not only become a reliable basis for the structure, but will also last a long time, protecting the structure from external influences.
Excavation
The construction of the foundation should begin with preliminary preparation land plot, it is thoroughly cleaned of debris, plants and trees, the fertile soil layer is removed. Then markings are made and all measurements specified in the building project are transferred to the work site. To do this, use pegs and a rope. First of all, the facade walls of the building are marked, then two other walls are placed perpendicular to them.
At this stage, it is important to control the evenness of the diagonals; at the end of the markup, a rectangle is obtained that compares all the diagonals.
Beacons are hammered into the corners of the future structure, keeping a distance of 1 m between them. The next step is to install a wooden blind area, on which the ropes will be pulled. Some craftsmen simply mark the dimensions of the foundation on the ground using lime mortar. Then a trench is dug, its depth should correspond to the thickness of the sand cushion and tape.
Since usually the thickness of the sand cushion does not exceed 20 cm, a trench is made for a shallow foundation with a width of 0.6-0.8 m and a depth of 0.5 m.
In the event that the project provides for the construction of heavy structures with stairs, a porch and a stove, it is recommended to dig a foundation pit. To make a pillow with a thickness of 30 to 50 cm, crushed stone and sand are used, the most common option is a pillow consisting of two layers: 20 cm of sand and 20 cm of crushed stone. For dusty soil, it is necessary to additionally place geotextiles in the trench.
The pillow is covered in layers: first of all, a layer of sand is evenly distributed, it is well compacted, moistened with water, then gravel is poured and compacted. The pillow should be placed strictly horizontally and covered with waterproofing in the form of roofing material on top.
formwork
An equally important point in laying the foundation is the assembly of the formwork. To make it, use such panel materials as OSB sheets, plywood or boards with a thickness of at least 5 cm. In this case, the boards should be knocked down into shields. The formwork must be calculated in such a way that it turns out to be several centimeters higher than the future level of concrete. As for the height of the tape, it is made equal to or less than the depth of the foundation, as a rule, it is 4 tape widths.
Prepared shields are fastened together with nails or self-tapping screws, after which they are additionally supported with pegs. It is worth paying attention to the fact that all fasteners do not stick out and go inside the formwork. If this is ignored, then they will end up in concrete after pouring and can provoke the appearance of cracks or chips.
The formwork of a shallow strip foundation is also additionally reinforced with struts made of timber with a section of 5 cm, such supports are placed externally at a distance of 0.5 m.
In addition, in the formwork, you need to prepare holes for communications in advance and insert pipes. The inside of the structure is covered with polyethylene, it will enhance the waterproofing and reduce adhesion to concrete.
It is also allowed to use a fixed type of formwork made of extruded polystyrene foam.
Reinforcement
The device of this type of foundation includes mandatory reinforcement. The fittings can be both knitted with wire and welding can be used, but the latter option is not recommended for connecting metal rods, since corrosion will appear at the attachment points over time. For mounting the frame, a minimum number of rods is required, at least 4 pieces.
As longitudinal reinforcement, material with a ribbed section of class AII or AIII must be used. At the same time, the longer the rods are, the better the frame will turn out, since the joints reduce the strength of the structure.
The transverse parts of the frame are assembled from smooth and thinner reinforcement with a diameter of 6 to 8 mm. To install a shallow base, two reinforcing belts consisting of only 4 longitudinal rods will be sufficient. It is important that the edges of the reinforcement move away from the foundation by 5 cm, and the step between the vertical fasteners is at least 30-40 cm.
The crucial moment in the work is the manufacture of the corners of the frame: the bars must be bent in such a way that the entrance to another wall is at least 40 mm from the diameter of the bars. In this case, the distance between the corners formed by vertical jumpers should be half the distance in the wall.
fill
The completion of the installation of the foundation is the pouring of concrete mortar. Experts recommend using factory-made concrete of grade not lower than M250 for this. If the solution will be made independently, then you should first prepare a concrete mixer, since it will be difficult to do it manually. The base must be poured with a solution immediately, for this it is evenly distributed over the entire surface and compacted. Each layer of pouring should be carefully aligned to the mark applied to the formwork.
Experienced craftsmen who have made more than one hundred foundations advise sprinkling concrete with dry cement after pouring, this will improve its quality and the top layer will set faster.
On the complete solidification of the base, as a rule, take one month, after which you can continue construction works.
Basic Mistakes
Since the foundation is the main component of any structure, its laying must be carried out correctly, especially for a shallow strip base, which is installed on loose soils and clay soils. Any mistake made during its construction can nullify all construction work. At self-manufacturing foundation, inexperienced craftsmen make several common mistakes.
- Construction begins without calculations of the main dimensions and load on the foundation.
- The base is poured immediately into the ground, without sprinkling and making a sand cushion. As a result of this, in winter time years, the soil will freeze to concrete, drag and lift the tape up, as a result of which the foundation will begin to swell under the influence of frost, and the floor of the basement will crack. This is especially true in cases where there is no insulation.
- Choose the number of rods and the diameter of the reinforcement at your discretion. This is unacceptable, since the reinforcement of the foundation will be incorrect.
- Construction is not carried out in one season. The entire cycle of work should be distributed so that the laying of the foundation, the laying of the walls and the insulation of the blind area are completed before the onset of cold weather.
In addition, it is considered a big mistake to protect the concrete base with a film. Don't close it. The poured solution must have access to ventilation.
How to make a shallow strip foundation with your own hands, see the following video.
For the construction of houses of a small area, as well as various outbuildings, the best foundation option is a shallow foundation. Its construction will not take much time, and the whole process can be done independently. In order for the shallow-depth strip foundation to be as strong as possible with your own hands, you need to correctly calculate its parameters and strictly follow the pouring technology.
The main differences of the shallow base
The depth of a conventional foundation is at least 1.5 m, and in cold regions - up to 2 m. A shallow foundation is located at a depth of up to 70 cm, which greatly facilitates digging trenches and reduces construction time. Since the area of such a foundation is several times smaller, the consumption of building materials is also reduced. For its manufacture, not only concrete is suitable, but also red brick, as well as concrete blocks.
The shallow base also has its drawbacks: it is suitable only for the construction of one-story buildings of a small area; requires the arrangement of a drainage system on heaving soils. Such a foundation can be poured only in the warm season, and you can not leave it for the winter without a load. When it freezes, the soil pushes light foundation, damaging its integrity.
Foundation construction technology
The fastest version of the strip foundation is concrete monolithic. It is erected from blocks or bricks if it is not possible to prepare a large amount of mortar and pour the base at a time. To ensure that the construction process is not interrupted, everything should be prepared in advance necessary tools and materials.
So, for work you will need:
- roulette;
- plumb or level;
- pegs made of wood or iron bars;
- thick fishing line;
- pick and bayonet shovel;
- geotextile;
- sand;
- crushed stone;
- reinforcement with a section of 12 or 16 mm;
- formwork materials;
- polyethylene;
- concrete mortar;
- trowel.
The area for a shallow foundation should be relatively flat, with dense, uniform soil. The location of the house relative to the site is determined and a peg is driven in at the site of one of the corners of the facade. Measure the distance to the second corner and again put the beacon from the peg. A fishing line is pulled between the pegs, fixed, then perpendicular lines are drawn from each corner. By connecting the beacons into a rectangle, check the perimeter along the diagonals. If the angles and sides of the marking are equal, you can mark the inner perimeter, according to the project.
The width of the foundation tape is usually 40 cm, so inside the markup it is necessary to mark the internal boundaries of the base. To do this, 40 cm in both directions retreat from each outer corner along the stretched fishing line. These points are marked with beacons, and then they retreat 20-30 cm beyond the perimeter and drive in pegs. This is necessary for a more accurate designation of corners, both external and internal. In addition, during digging, closely spaced pegs can be accidentally hooked and knock down the markings.
The soil is taken out to a depth of 70 cm, the count is taken from the lowest marking point. The walls of the trenches must be strictly vertical, which is periodically checked building level. If the soil is crumbling, wooden supports should be installed as you move along the perimeter. When the trenches are ready, they check the horizontal level of the bottom, correct defects.
To avoid shrinkage and deformation of the strip foundation, a sand cushion is required. It is recommended to use coarse-grained river sand, which better resists compression. To protect the sand cushion from erosion, the bottom and walls of the trenches are covered with geotextiles. You can also take ordinary polyethylene, the main thing is that the sand does not mix with the soil. The material is spread inside the trenches, and its edges are brought up and fixed with something, for example, with bricks. This will prevent the geotextile from moving during sand compaction and rebar placement.
On the site with clay soil the thickness of the pillow should be at least 50 cm, but if the soil is predominantly sandy, 20 cm is enough. The sand is poured in 2-3 steps, each time carefully ramming it. For better compaction, layers of sand are shed with water. A layer of gravel about 10 cm thick is poured over the sand cushion, and it is also well rammed. After that, you can mount the formwork.
Assembly and installation of wooden formwork
For formwork, flat boards with a thickness of 2 cm or more, durable plywood, OSB boards are suitable. sheet material cut into pieces with a width of 40 cm, the boards are knocked into shields. It is more convenient to connect the formwork elements with self-tapping screws, then it is much easier to dismantle the structure. When assembling the shields, it should be borne in mind that the inner side should be as smooth as possible, otherwise all irregularities will appear on the walls of the foundation. Since the tree strongly absorbs water from the solution, the formwork should be upholstered with plastic wrap.
When the required number of panels is ready, proceed to the installation of the formwork. Parts of the formwork are placed on both sides of the trenches, leveled horizontally and in height, and knocked down along the upper edge with transverse bars at regular intervals. Further, the structure is strengthened with struts from the outside, so that when pouring, the formwork walls do not disperse. At the end of the installation, make sure that there are no gaps and cracks in the formwork, and that the walls are strictly vertical.
On the inner walls of the shields, the level of pouring the solution is noted; do this around the entire perimeter of the trenches so that the surface of the shallow foundation lies in the same horizontal plane. Instead of marking on the walls, many builders use fishing line: they stretch it inside the formwork and fix the ends with nails. This must be done after installing the reinforcing frame.
Frame installation
The reinforcing frame is knitted from reinforcement with a diameter of 12 cm or more. Bars are cut from the reinforcement along the width and length of the trenches, and then they are tied into a lattice. The dimensions of a standard cell are 30x30 cm. A soft wire is used for bonding, but it is undesirable to weld the frame: welding reduces the tensile strength of the metal, which leads to cracks in the base. In addition, the welded grating is more prone to corrosion.
Having laid the grate on the bottom, the frame is tied with reinforcement at the junctions. If the height of the base exceeds 30 cm, the reinforcing frame should be made two-level. To do this, knit the second layer of gratings, and then connect them to the bottom layer with vertical rods. The reinforcement should not touch the walls of the trenches and formwork, and also reach the level of pouring concrete. The metal protruding from the foundation will quickly rust from rain and snow, which means that the strength of the foundation will be reduced.
The strength of a shallow foundation directly depends on the quality of the concrete. For pouring, it is recommended to use a solution of brand M200 and higher. When making the solution yourself, pour 1 part of cement into the container, add 3 parts of sifted sand and 4-5 parts of fine gravel or crushed stone. If everything is done manually, the dry ingredients are first mixed, and then water is gradually poured in.
Although the height of the foundation is small, it is recommended to fill the trenches in layers. This will help to better compact the solution and distribute it more evenly. The first layer is poured with a thickness of 20 cm, leveled if possible and pierced to the bottom with a piece of reinforcement in several places. Particular attention should be paid to the corners. The second layer is poured immediately after the first, without waiting for the concrete to set. Again distribute the solution in the corners, under the bars of the frame, at the joints of the walls, get rid of air voids.
The last layer of concrete is leveled along the fishing line, the surface is smoothed with a trowel, and then sprinkled with dry cement through a sieve. This contributes to a faster setting and hardening of the mortar, in addition, the surface sprinkled with cement does not crack when dried. The finished foundation should be covered with a film from scorching rays and from rain for 28 days, until the concrete is completely dry.
To extend the service life of a shallow foundation, it is recommended to insulate its outer walls with polystyrene foam boards or polyurethane foam. Along the perimeter of the base, it is desirable to make a blind area 1 m wide, and additionally equip drainage ditches in flooded areas.
The construction of such a foundation has slight differences. Brick can be used second-hand, the main thing is that it be burnt and whole. Blocks for the foundation can be made by hand, which will save a little on materials.
So, the construction of the foundation is carried out as follows:
- mark the site and dig trenches;
- lay geotextiles, a sand cushion and a layer of rubble;
- they knit and lay out reinforcement, the top of which should not reach about 5 cm to the edge of the trench;
- fill the pits with concrete flush with the ground, level the surface;
- after setting and hardening of the concrete layer, lay out several rows of blocks or bricks with mandatory dressing of the seams;
- the outer walls of the foundation are insulated, and covered with cement plaster on top.
If the foundation is intended for utility rooms, you can not insulate it, but immediately plaster the masonry with mortar. Subject to the described technology, the foundation will last for several decades.
Video - Do-it-yourself shallow strip foundation
The shallow strip foundation has become popular for the construction of private houses due to its versatility and the possibility of building without the use of heavy equipment and for relatively little money. How to build a shallow strip foundation with your own hands?
When is MZLF applied?
A shallow strip foundation (MZLF) is a type of strip foundation with a laying depth of no more than 70 cm. This type of foundation has become widespread in individual construction due to several significant advantages:
- relatively low cost
- a small amount of earthworks,
- no need to use heavy equipment,
- applicability on different types of soil,
- low cost of building materials.
It is possible to build on it houses up to 3 floors from timber, logs, frame, brick with lightweight masonry, from foam concrete.
The shallow foundation is suitable for both non-rocky and heaving soil. You can not do it on biogenic soils: peat, sapropel, and also on clay.
Types of MZLF
A shallow strip foundation can be either monolithic or prefabricated. The monolithic foundation is a concrete reinforced tape, which is located along the perimeter of the building and under the bearing walls. In the case of a prefabricated foundation, this tape is made from foundation blocks held together with cement mortar. It will take much less time to create a prefabricated foundation, but its service life is shorter than that of a monolithic one.
Combination of pile and strip foundation - pile-tape shallow foundation. The tape in this case rests on screw or bored piles, a sand or gravel pillow is made under it. pile foundation do on difficult soils or with elevation changes on the site.
Construction order
Before making a shallow strip foundation, it is necessary to conduct a geodetic examination to find out
- soil composition and quality,
- the depth of its freezing,
- ground water level.
These parameters affect the choice of the type of foundation and the depth of its laying. However, if you want to save on expensive expertise, it is enough to drill pits in several places on the site to assess the quality of the soil.
- Clay soil can be rolled into a ball with your hands.
- Loam can also be rolled into a ball, but it will be cracked.
- At the same time, sandy loamy soil will partially crumble.
- Sandy soil cannot be rolled into a ball.
The construction site must be cleared of debris and plants, trees uprooted, and the fertile soil layer removed.
Next, markup is carried out - the dimensions of the house are transferred to the site. To do this, you need a rope and pegs. First of all, mark the front wall of the house, which looks out onto the street. Next, two other walls are built perpendicular to it. To check whether a rectangle is even, compare its diagonals. There are beacons in the corners. At a distance of about a meter from this contour, a blind area is installed from boards, on which ropes are pulled, showing the dimensions of the strip foundation. It is possible to apply dimensions directly to the ground with lime mortar.
After that, they dig a trench. Its depth is equal to the thickness of the tape plus the thickness of the sand cushion. The thickness of the pillow is usually 20 cm. Usually, a trench for a shallow strip foundation is made 0.5 m deep and 0.6-0.8 m wide.
Under heavy structures, such as a stove, a porch, a ladder, they dig pits.
The pillow is made of sand, crushed stone or a mixture of them, 30-50 cm thick. A common option is also a two-layer pillow: 20 cm of crushed stone and 20 cm of sand. If the soil in the area is dusty, then geotextiles should be laid in the trench before backfilling the pillow.
The pillow is poured in layers, compacting each layer. If it is two-layer, first pour 10-15 cm of sand, compact it. To facilitate this task, the sand is wetted. Next, gravel is poured and also tamped. The surface of the pillow must be strictly horizontal, this can be checked using a level. A waterproofing material is laid on top - roofing material.
Monolithic MZLF
Next, collect the formwork. For it, boards or panel materials are used, such as plywood, OSB and others. The board must be at least 5 cm thick. The boards are knocked down into shields. The formwork should be a few centimeters above the expected concrete level. The height of the tape above the ground must be less than or equal to the depth and equal to 4 tape widths.
The shields are fixed with pegs, interconnected with screws or nails. Fasteners must not protrude into the formwork. If they are in concrete, cracks may appear or even a piece of concrete may break off. Also, the formwork for a shallow strip foundation is additionally strengthened with inclined supports (struts) made of timber with a cross section of at least 5 cm. Supports are located on the outside at a distance of about 0.5 m. Holes for communications must be drilled in the formwork. Pipes are inserted into them.
From the inside, the formwork is lined with polyethylene for waterproofing and reducing adhesion to concrete. You can also use fixed formwork made of extruded polystyrene foam.
Reinforcement
The device of a shallow strip foundation necessarily includes reinforcement. The armature is knitted with knitting wire. The use of welding to join the bars is not recommended as these are the areas where corrosion is most likely to occur. Reinforcement schemes are shown in the figure.
The minimum number of bars for the frame of a shallow strip foundation is 4 pieces. Longitudinal reinforcement must be class AII or AIII, have a ribbed section. The longer it is, the better - each connection reduces the strength of the frame. For the transverse parts, thinner smooth reinforcement (6-8 mm) is used. For a shallow foundation, two reinforcing belts are sufficient, only 4 longitudinal bars. The reinforcement should be 5 cm from the edges of the foundation. Between the vertical jumpers there should be 30-40 cm.
It is especially important to properly reinforce the corners. To do this, the bars are bent in such a way that the entrance to another wall is at least 40 bar diameters. At the same time, near the corners, the distance between the vertical jumpers should be half that in the wall.
fill
It is better to take factory-made concrete, brands not less than M200 (for wooden houses) and M250 (for brick ones). When making it yourself, it is better to mix the concrete not by hand, but in a concrete mixer.
It is advisable to fill the entire foundation in one go. Concrete is poured in layers, each layer is leveled and compacted. For this purpose, it is better to use a vibrotamper. The last layer is leveled according to the mark applied to the formwork. Professional builders who have already made more than a dozen foundations recommend sprinkling concrete on top with dry cement. This is necessary so that the top layer grabs faster. The foundation freezes for about a month.
Anti heave
Before you make a tape shallow foundation on loam, you need to know that anti-heaving measures are needed for such soil:
- drainage,
- waterproofing,
- warming.
For more information about the insulation of the foundation, see the video:
Important! It is highly desirable to complete the entire cycle of work (build a house completely) in one season so that the foundation does not remain unloaded for the winter. Otherwise, the forces of frost heaving can squeeze the foundation out of the ground, deform or break. If it is not possible to complete the house before the cold weather, then the ground around the foundation must be covered with any heat-insulating material (straw, sawdust). Snow on the site does not need to be removed.
MZLF on piles
The foundation on piles is made on difficult soils. For this, screw or bored piles are usually used. A sand cushion is poured under the tape. It will resist heaving of the soil.
Bored piles are made right on the site. To do this, wells are drilled, pipes, a reinforcing frame are placed in them and poured with concrete. The depth of the wells should be below the freezing level of the soil.
The pile reinforcement must be connected to the tape frame. To do this, it must rise above the sole of the tape by at least 40 cm. If used screw piles, then holes are drilled in them, reinforcement is threaded into them and connected to the tape frame.
A shallow strip foundation, both monolithic and prefabricated, can be made independently. You can build houses on it different material and different number of floors (up to 3 floors), it is used on different types of soil.
Economical and at the same time maximum solid foundation- the dream of every novice developer. But is such an option possible? Quite. Direct confirmation of this is a shallow tape base. The arrangement of such a foundation does not require large financial and time costs, but the result of the work is very pleasing - you get a high-quality and durable foundation. Moreover, you can even build it with your own hands, without the involvement of professional builders. To make sure of this, let's look at each stage of the construction of a shallow foundation. And in addition, we advise you to watch the installation video - it will allow you to understand in more detail the technology of laying the base.
Distinctive features of a shallow foundation
Before proceeding to the analysis of the laying technology, we will designate the main features of the shallow-depth strip base:
- is a frame monolithic tape from reinforced concrete, outlining the perimeter of the future structure;
- costs two times cheaper than a deep-seated foundation;
- suitable for the construction of one- and two- and three-story buildings made of wood, concrete, stone and brick;
- can be used on non-rocky areas, as well as on weakly, medium and strongly heaving soil;
Important! In the last two cases, it is necessary to ensure high-quality soil drainage.
- arrangement involves a minimum amount of land work;
- makes it possible to build a small basement or cellar in the perimeter of the building;
- for laying it is not necessary to use special equipment.
A shallow foundation cannot be built on frozen ground, so all work must be completed before the onset of frost. The laying of the base is carried out in four stages.
Stage 1: Trench preparation
The first step is to prepare trenches into which concrete will subsequently be poured.
First, mark the site on which the foundation will be located. Then accurately determine the corners of the future design - they should be as even as possible. Next, proceed to create the foundation - dig trenches around the perimeter of the marked area. The optimal foundation depth is 50 cm. The width of each trench should be at least 60-80 cm.
When the recesses are dug, you need to compact the soil - arrange a special pillow on it. If the site is based on silty fine sand, the soil must first be covered with geotextile - it will prevent the site from silting up and protect the foundation cushion from weeds, which are likely to grow in it due to high humidity.
The pillow itself should reach a height of 30-50 cm - this will be enough to give the foundation the necessary strength. First, sand is poured with a layer of 15-20 cm. It must be thoroughly moistened and compacted. Then fill in 15-20 cm of gravel. Moisten and tamp the base again. Further, waterproofing is carried out - sheets of roofing material are laid.
When the work is completed, check the level of the resulting base surface - it must be strictly horizontal.
Stage 2: Arrangement of formwork
The next step is to work with the formwork. For its construction you will need a large number of boards. Keep in mind that when concrete is poured onto the formwork, serious mechanical stress will occur, so stock up on a solid board - its thickness should be at least 5 cm.
Boards need to be knocked down in the form of shields. The optimal connection pitch is 80 cm. If the pitch is wider, the structure will not be strong enough. Finished wooden panels can be fixed to the base using props or support bars. The latter must be installed every 60-70 cm. The recommended section of the bars is 50x50 mm. The shields must be tightly fixed between the installed bars or supports. After mounting the formwork, cover the panels with dense polyethylene or glassine.
From the outside, it is also desirable to strengthen the formwork structure with special supports so that it does not deform during subsequent installation work.
Stage 3: Base reinforcement
High-quality reinforcement is a guarantee of the integrity and durability of the entire structure of a shallow foundation, so this step should not be skipped in any case.
First, build a reinforced frame. To do this, prepare metal rods 14-18 mm in diameter. Their length can be any, but experts recommend using long products - 2-5 m. Remember: the longer the rods, the fewer connections and the stronger the base of the foundation. Metal products are laid around the entire perimeter of the foundation on a pillow, thereby forming a frame.
For the arrangement of a reinforced skeleton, rods of a smaller section are usually used - up to 10 mm. The length of the products should be slightly wider than the trench. All reinforcement is installed strictly perpendicular to the frame elements. There are two ways to connect them: more reliable - electric welding, and more affordable - wire tying. The latter must be very flexible in order to be easy to work with.
Advice. For the convenience of mounting the reinforcing skeleton, you can use trim plastic pipes: saw them on a circular saw to make rings 5 cm high, install the resulting products on the base and fix the reinforced structure on them.
Stage 4. Concrete pouring
The most important stage is the direct pouring of the foundation. It can also be divided into several stages:
- Mixture preparation. If you are laying the foundation yourself, you will probably decide to prepare the concrete mix yourself. There is nothing difficult in this. The main thing is to buy quality Consumables: concrete itself, crushed stone and sand. It is desirable that the latter be of a large fraction - it adheres better. The mixture is made from concrete, sand and water in a ratio of 1:3:1. After thorough mixing, 5 parts of crushed stone are added to the composition.
- Filling the mixture. When the composition is thoroughly mixed, you can pour it into the prepared trenches. To prevent the formation of air chambers during the solidification of the foundation, the concrete must be compacted after laying. This can be done both manually - using a wooden rammer, and using a special vibropress. The composition must be poured not in one go, but as it is compacted. Check the level regularly while the concrete is drying.
- After the final solidification of the foundation, fill the remaining layers between the trenches of the foundation with earth and tamp it down.
As you can see, it is really not difficult to equip a shallow strip foundation with your own hands. Stick to the general technology and follow the installation rules that professional builders have long taken out - compliance with these two conditions will lead you to a positive result, even if you are pouring the foundation for the first time.
Shallow strip foundation: video
Strip foundation: photo
