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Choosing a foundation for a house on heaving soils. Shallow foundation on heaving soils: types of foundations and their features Do-it-yourself shallow foundation on heaving soil

Wiring
05.08.2023

To perform shallow strip foundation(MZLF) on heaving soils, it will be necessary to provide a set of protective measures. This technology is relevant for buildings that do not plan to have a basement. The construction of deep foundations in this case will lead to unreasonable cost overruns.

Soil heaving is a natural phenomenon that occurs when two factors are present simultaneously:

  • temperature below 0°C;
  • moisture.

Water is a unique substance. It is the only one of all matter on the planet that expands when cooled (the density of fresh water is approximately 1000 g/m3, and the density of ice is 917 g/m3). If there is moisture in the soil in winter, the soil increases in volume. In this case, tensions arise that try to push the foundation out of the ground.

Uniform deformations are not so dangerous for a building, but during heaving they are not the same. In the middle of the house, the soil temperature is higher, and the forces of frost heaving are weaker here. At the edges of the building they are strong, since the heating from the interior is less. The outer walls of the house rise more than the inner ones, which leads to the appearance of cracks in the foundations, walls, and partitions.

The action of frost heaving forces.

What soils are classified as heaving?

Before designing and constructing the foundation, it is necessary to carry out geological surveys. They will help determine which layers of soil lie on the site. If it is not possible to order a professional study, you can conduct it yourself by extracting test pits or manual drilling. When determining the type of soil, you should be guided by the descriptions in GOST “Soils. Classification".

According to this standard, soil is divided into 5 groups:

  • excessively heaving;
  • highly heaving;
  • medium heaving;
  • slightly heaving;
  • non-puffy (conditionally).

For all groups, except for the last option, measures must be taken to protect the shallow strip foundation on heaving soils. Conditionally non-heaving soils include coarse clastic types, coarse and medium fraction sand. These materials filter moisture well, so it goes to the lower layers. At the same time, the level of location groundwater should be below the depth of support of the foundations.

Heaving soils do not allow water to pass through well, so precipitation easily accumulates in the layer. These types include clay, loam, and sandy loam. You also need to get rid of heaving in fine sandy and dusty soils. Construction on the latter is not recommended; it is better to completely replace the soil with coarse sand.

Scope of application of MZLF

A shallow strip foundation is used for small buildings without a basement. This option will reduce the financial and labor costs of constructing a strip under the house by reducing the volume of concrete and the amount of reinforcement. In this case, the strength characteristics of the soil must be sufficient to support the building. First you need to perform a calculation.

MZLF device diagram.

This type of foundation is also used when water occurs in the ground at a distance of 1.5 m or more. In this case, it is impossible to use a deep tape without costly water reduction measures.

MZLF is most often installed under buildings made of relatively light materials:

  • wood;
  • wooden panels (frame houses);
  • lightweight concrete (foam concrete, aerated concrete, etc.).

The depth of the tape may vary. Most often, it is assigned within the range of 70 - 100 cm. The exact value depends on the strength characteristics of the soil, the number of storeys of the building and the materials used for construction. In this case, the location of the ground moisture level should be 50 cm below the level of the base of the foundation. Otherwise, there is a risk of structural damage.

How to protect MZLF from heaving on clay soils

The most common way to deal with heaving soils is to lay the base of the foundation below the freezing mark (determined by). But in many regions this mark is too deep, the cost of construction increases greatly.

A set of measures to protect MZLF from heaving.

When installing a shallow strip foundation on heaving clay soils, protective measures are carried out in a complex. In this case, they are guided by paragraph 11. It is important to prevent exposure to cold and moisture at the same time. MZLF protection is performed in the following order:

  • from non-foaming material. It is prescribed with a thickness of 30-50 cm. It is made of coarse or medium sand. Sand is also used to fill cavities on the sides of the foundation. This approach will eliminate the effect of heaving soils on the side surface of the structure. A layer of geotextile is placed under the sand cushion to prevent siltation.
  • at the level of the base of the foundation. The pipe is laid at a distance of no more than 1 m from the side wall of the tape. The depth is set at 20-30 cm below the base of the foundation. The slope of the drainage pipe depends on the diameter of its cross-section.
  • and the vertical surface of the strip foundation. The function of insulation for heat and moisture can be taken over by extruded polystyrene foam (for example, penoplex). The material is attached to the entire height of the tape, including the base. It is prohibited to use cheaper foam plastic instead of penoplex. It has a much smaller resource.
  • Insulated blind area. This element also performs the function of waterproofing, preventing atmospheric moisture from entering the foundation. By laying penoplex under the outer layer of the blind area, it will be possible to prevent freezing of the soil in the immediate vicinity of the building.
  • Storm drainage. When landscaping the area, it is important to provide for the effective removal of excess moisture from the site.

The required slope of drainage pipes depending on the diameter.

The construction of the foundation on clay heaving soil is carried out in summer period. It is important to load the structure before the onset of cold weather. If construction is forced to stop, it is necessary to carry out a full range of measures.

Alternative options

Shallow tape has a reduced load-bearing capacity. It is not recommended to use it for massive buildings. If you need to build a brick or concrete building on heaving soil, it is better to give preference foundation slab shallow laying.

Also, you should not use MZLF when the groundwater level is located at a distance of less than 1.5 m from the soil surface. In this case, under brick or concrete house(including lightweight concrete) a non-buried slab is suitable. For frame or wooden house You can use metal screw piles.

Proper selection of the type of foundation and adherence to the technology of its construction will prevent the negative impact of heaving soils. It is important to take all steps to protect the structure from cold and moisture.

Heaving soils have a number of features. In particular, the process of soil heaving begins during the period of freezing of the earth's thickness. Most often it occurs on clayey, loamy and fine sandy soils, where the influence of groundwater is strong. When the soil freezes to a certain depth, the water that the frost reaches increases in volume and lifts the top layer. Soils are called heaving because of their ability to swell and deform the earth in winter, undermining or breaking structures standing on them, including fairly heavy foundations. Building on such soils must take into account their destructive influence.

Heaving soils and features of construction on them

This is especially true for regions with high level water content underground and too cold winters. When the soil freezes to a great depth, the bulk cushion is not always enough. On such heaving soils, construction on a shallow foundation is used. Large construction corporations place structures on a reinforced concrete slab base. In private construction, it makes sense to lay a sand-crushed stone cushion (or bedding) made of a material that is not subject to heaving under the foundation of the house, which allows you to keep the frame from moving during the period of soil freezing. There are two options for laying a foundation on heaving soils with your own hands:

  • Shallowly buried on a leveling bedding;
  • Shallowly buried on a cushion made of a mixture of loose materials that are not subject to deformation during heaving.

Technologies make it possible to supplement the installation of an airbag for a building under construction with polymer insulation materials that reliably protect the ground under the structure.

On heaving soils, depending on their classification, you can install a structure for the construction of small houses, cottages, outbuildings and other structures on a strip foundation; you can do this yourself. The only thing that owners of a plot located on heaving soils should pay attention to is insulating the ground around the house and creating a warm microclimate under the base of the house.

It is worth considering that the material for the walls of the house should not be heavy. Tape option laying is often used to save materials using reinforcement.

Selecting a base

If it already happens that your site is located near a body of water or in a region with very cold winter, then when designing buildings, consider which option for laying the foundation will be preferable in terms of time and financial costs. To neutralize the negative impact of natural phenomena, choose one of the options for laying the base:

  • On an airbag using bulk materials;
  • On a bed of crushed stone and sand with an admixture of expanded clay and the creation drainage system allowing for high-quality drainage from the structure;
  • Tape version with reinforcement and increasing the level of rigidity of the house with a reinforcing belt;
  • Belt version with installation of pillars or piles (columnar type);
  • Slot design (when concrete is poured into trenches directly into the ground without the use of formwork).

Before you begin, study the geodetic map, prepare a project, bring in the building materials necessary for the construction of the building, and feel free to start realizing your dream. You will have to do this with your own hands, so you will have to use more physical labor, less equipment. The time for shrinkage of this type of foundation should not exceed one season: the design of a house for a shallow strip base does not involve shrinkage.

Important! The foundation must be laid to a depth below the freezing level to prevent the building from cracking in the future. For pouring, use high-strength concrete of the highest grade, which is frost-resistant and water-resistant.

Device

When building on heaving soils, the foundation laying technology is as follows:

  • marking;
  • digging trenches;
  • pillow placement;
  • if necessary, laying a drainage pipe;
  • blind area with polymer insulation;
  • waterproofing;
  • installation of reinforcing mesh;
  • pouring concrete with or without formwork or laying blocks;
  • insulation of the foundation.

As you can see, there is nothing complicated. You can do this with your own hands, without resorting to outside help.

The first thing you need to do, and what the final result of your work will depend on, is to correctly mark the future house; trenches must be dug under all load-bearing walls, which will bear the maximum load. The width of the trench should be greater than the thickness of the planned walls to reduce the load.

Pegs should be driven into the corners of the future structure and along the load-bearing walls and a plan should be outlined. At the next stage, install a blind area with a retreat of several tens of centimeters from the pegs and wrap them around the perimeter with a rope, which will act as a ruler.

Laying work

First you need to dig trenches for the tape filling. The walls of the moat should be as smooth as possible to reduce the consumption of building material. If possible, use a mini bulldozer. After the technique, it will be enough to level the walls and proceed to the next stage.

If not, then you will have to dig the trenches yourself. The depth of the trench depends on the level of soil freezing in the region of residence; it should be below this line. IN middle lane In Russia, the freezing level ranges from 50 cm to 1.5 m. In cold regions it reaches 2 m. Geotextiles should be laid in prepared trenches to avoid adverse effects on the drainage system, consisting of one or more pipes. Geotextiles will protect pipes from corrosion.

Sand 20-30 cm thick is poured onto the bottom. To give density, it is better to fill it with water and compact it thoroughly. You should not add sand if its share in heaving soils in your region is more than half.

We are making a drainage system. Cast iron or steel pipes with a large cross-section, which are laid parallel to each other in prepared trenches with a slight slope and discharge into a drainage pit.

To make the pillow, sand and crushed stone of the required fraction are used (preferably gravel). In some cases, expanded clay materials are added to make the structure stronger. The pillow can be made by mixing materials, but it is better to lay it out in layers. It is advisable to fill the layers with water and compact them in order to avoid porosity and give the pillow strength. A tightly laid cushion will strengthen the load-bearing capacity of the foundation.

Waterproofing

A layer of waterproofing must be applied to the pillow. This can be ordinary dense polyethylene film, pieces of old roofing felt or other bitumen-polymer material. Waterproofing materials must be laid so that the edges extend beyond the formwork.

When the airbag is laid, we proceed to install the formwork. Formwork is prepared from scrap materials. It is better to take boards with a perfectly smooth one side so that the walls are initially smooth and do not require much effort to cover them. The foundation will protrude above the ground, forming the plinth. That is why the formwork should be above ground level by the distance that you plan to use for the height of the base.

Lines up first inner part formwork with stop. Then the outer part is prepared, which is strengthened from the outside with spacers. It is advisable to nail a strip between the inner and outer parts of the formwork so that during pouring of concrete the structure cannot expand and move to the side.

Reinforcement

In order for the concrete mixture to acquire the necessary strength, it should be based on a mesh of reinforcement. The mesh is woven from reinforcement of 12 and 20 diameters and tied together with ordinary wire. Each row must have at least 4-6 reinforcement bars. Reviews about this weaving are positive, since you can do it yourself. The mesh is easy to knit, and a concrete foundation with reinforcement lasts much longer, since this combined option is less susceptible to the negative effects of temperature changes.

For corner fastenings, you will need to additionally use reinforcement corners. When installing a grate on the bottom of a trench, it is advisable to use supports made of plastic pipes. This is done so as not to damage the waterproofing layer with the sharp ends of the reinforcement.

The finished mesh should be laid carefully, weaving it into a single structure to form a monolithic rigid frame. Reinforcement is one of the important tasks, since, in essence, it represents the skeleton of the foundation.

Insulation of the base of the house. In very cold European countries it has been experimentally found that important role When building houses on heaving soils, insulation plays a role. At modern technologies For the manufacture of building materials from polystyrene foam, it does not make sense to prepare additional insulation systems. Expanded polystyrene is a very high-quality insulation material; it is not afraid of getting wet, and its service life is almost unlimited. Reviews from owners of houses with this type of installation speak for themselves. It can be used instead of formwork, and can be additionally laid as a blind area around the building. This blind area serves as reliable protection against cold penetration under the house.

The earth has the ability to absorb energy, and under a layer of insulation, the temperature situation under the house remains stable even in a very cold winter, and there is practically no heat loss. The house itself becomes a source of heat.

When laying the blind area, you need to decorate the material on top. Expanded polystyrene is not intended for walking. Therefore, ceramic tiles should be laid over the entire area of ​​the blind area or concreted in a thin layer. To prevent the house from getting wet, it is better to do this on an incline.

It is better to lay the blind area at a distance of at least 1 meter around the perimeter of the entire building.

Pouring concrete mixture

The final stage of laying the foundation is pouring concrete into the prepared strips. The concrete mixture is prepared immediately before starting work. It is made from sand and cement. In some cases, sand crushed stone of the finest fraction is added. For construction on heaving soils, it is better to use high-strength cement. Saving in this case is not safe for life.

During the pouring process, the mixture must be vibrated using a stick or special tool in order to expel excess air bubbles. This will give the concrete additional strength.

The concrete mixture must be compacted thoroughly. The top of the concrete should be as level as possible. Achieve flat surface You can use a stretched rope or a spirit level. The smoother the concrete layer is laid, the easier it will be to lay it on the base. construction material for pushing out walls.

The columnar base of the house is the most reliable if you want to save money. Instead of reinforcement, reinforced concrete pillars are installed at the corners and along the perimeter of the trench. Such foundations can be laid where it is not possible to use concrete on a monolithic basis, for example, in wetlands or on land with a high content of underground groundwater. Do these reinforced concrete structures you can do it yourself.

Shallow strip foundation on heaving soils


Features of heaving soils and rules for arranging a strip foundation. Description of work on laying a shallow foundation.

Heaving soil is characterized by the fact that it expands when it freezes and collapses when it thaws. The foundation moves along with the soil, rising and falling depending on the weather and time of year.

As a result of uneven displacement of the foundation, the walls of the house may warp, the foundation may deform, and the structure itself may collapse. Experts recommend using a shallow foundation for such soils, since correct installation it is not negatively affected by ground movements.

Problems with heaving soil

Heaving soil is not entirely suitable for construction due to uneven shrinkage. This shrinkage causes problems such as bending and deflection, shear and horizontal displacement, roll and skew of the base. This, in turn, leads to deformation and destruction of the structure, disruption of the appearance and functionality of the house.

But if you decide to build on such land, the following methods will help you avoid problems:

  • Base concrete foundation made expanded in the form of a trapezoid. This increases the stability of the structure and reduces the influence of heaving forces;
  • Increasing the width of the foundation, due to which the level of heaving on soils is neutralized;
  • The walls of the trench where the foundation is installed must be lined with waterproofing materials. This will protect the base walls from the adjacent soil;
  • On the side and bottom of the base, the heaving soil is replaced with gravel or sand, making a backfill from these materials;
  • Along the outer perimeter of the foundation they lay thermal insulation materials, under which the soil does not freeze and does not allow heaving to appear on the ground.

It is important to choose the right type of base. The most suitable in this case is the construction of a shallow foundation. It copes well with loads and is not subject to uneven shrinkage and destruction. In addition, this design is easy to install and is suitable for most buildings.

Features of a shallow foundation

Strip foundation is a common type of foundation for Vacation home or a bathhouse that you can install yourself. The design is distinguished by high strength and stability, reliability and durability, and affordable cost. However, it should be borne in mind that this type of foundation is suitable for soils with a freezing depth of up to 1.5 meters.

The construction of this foundation on heaving soils involves a shallow pit with a depth of up to one meter. Waterproofing materials must be laid inside the pit. Then they make wooden formwork and arrange reinforcing belt from steel rods. And the base is covered with thermal insulation. Let's take a closer look at how to install a shallow strip foundation.

Foundation installation

  • Calculation and design of the foundation. When developing a foundation project, do not forget about laying utility networks. In this case, they take into account how the water supply and sewerage will be routed, how heating and ventilation will be arranged;
  • Site preparation, which includes removing debris and leveling the surface;
  • Marking the foundation on the site using pegs and rope. Pegs are installed in the corners, on the internal and external boundaries of the base. A rope is pulled between the pegs. For more accurate markings, laser levels are used;
  • You should dig a pit, the suitable depth of which is 50-70 centimeters;
  • Waterproofing materials are placed on the bottom and walls of the pit, such as polyethylene film, roofing felt and other rolled materials;
  • The pit is covered with sand in a layer of 20-30 centimeters and thoroughly compacted;
  • They make formwork from wooden planks or wood chips;

  • Another layer of waterproofing is placed in the formwork and only then reinforcement is made;
  • For reinforced mesh, metal rods with a diameter of 12 centimeters are used, which are installed in two separate belts with five rods and jumpers in each;
  • The rods are fastened with wire. Welding should not be used, as corrosion will form at the fastening points!;
  • The formwork is filled with concrete mixture. For bathhouses and buildings with low loads, choose concrete of a grade not lower than M200, for cottages and reliable country houses - not lower than M300;
  • The top layer of reinforced mesh is placed in the still wet concrete mixture. This distinguishes the installation of a shallow foundation from other types of foundation;
  • After the concrete has hardened, thermal insulation is laid around the perimeter. A suitable material solution would be extruded polystyrene foam. It reduces the risk of soil freezing and does not allow moisture to pass through, increases the strength and service life of the structure;
  • Finally, the insulation is covered with sand and the layer is compacted. If necessary, you can install a blind area. She will complete appearance foundation, will subsequently drain water from the foundation and the house.

Other types of foundation for heaving soil

In any case, for heaving soil you need to use only a shallow or shallow foundation, not necessarily a strip one. It can be pile, columnar or slab base. If the pillars can be installed below the freezing point, a columnar base is used.

A shallow or non-buried pile foundation is not a very popular foundation, but it is also used for construction on heaving soil. Installation of this structure is complicated by the fact that careful calculation is required. In addition, it is only suitable for frost depths greater than 1.5 meters and in the presence of a good drainage system.

A pile foundation increases the mass and increases the shrinkage of the building and does not allow for the construction of a basement or basement. Installation is labor intensive and big amount minor physical work. But the structure is quite easy to construct. In addition, installation takes only 1-3 days, and construction of the house can begin on the day the foundation is poured.

The columnar foundation is suitable for loam and soil with close groundwater, for swampy and damp areas. However columnar bases can only be used for buildings with light loads without ground floor and foundation. This is the best option for building a bathhouse or a compact country house.

Support posts are installed along the perimeter of the future building and screwed into the ground below the freezing level. This foundation is distinguished by its affordable cost, ease and efficiency of installation, reliability and durability. It does not require serious waterproofing and is characterized by simple installation of communications.

A slab foundation is the strongest, most reliable and durable foundation, which consists of a monolithic slab of a large area around the perimeter of the house. It is suitable for every type of soil or soil and for every type of building. Reduces building pressure and moves smoothly with the ground. In this case, changes in the soil are evenly distributed over the surface of the slab, which prevents deformation of the walls of the building. Besides, monolithic slab if necessary, it will serve as a floor for the basement floor.

But a slab foundation requires the use of special equipment, which complicates installation and increases financial costs. In order for the base to serve for a long time, not to deform or collapse, it is important to choose the right type of structure, choose high-quality materials and follow the installation technology. To avoid mistakes and problems, contact professionals!

The specialists of the MariSrub company will analyze the soil and land plot in order to choose the right type of foundation, correctly calculate and design the foundation. We carry out installation, insulation and waterproofing of the structure efficiently and quickly.

We carry out a full range of works, including installation of foundations and roofs, design of a house or bathhouse and production of lumber, installation and connection utility networks. We do the final finishing of the building, install windows and doors. If necessary, we will install a reliable drainage system and blind areas. We guarantee quality and timeliness of work!

Such foundations require accurate consideration of soil properties, place increased demands on the strength of building elements, the right choice constructive solutions and quality of construction work.

There are serious theoretical justifications and great successful practice in the construction of low-rise buildings from any materials on these foundations. At the same time, some negative experience of using shallowly buried foundations, upon expert study shows that The main reason for such negative situations is errors in the design and construction of buildings.

A necessary condition for using this type of foundation in a particular case is the Customer’s willingness and ability to carry out high-quality work for research, design and construction.

Application of such foundations certainly justified for wooden (log, lumber) or frame buildings whose walls are better able to withstand deformation.

Thermally insulated shallow foundation (TFMZ)

Heat-protected shallow insulated foundation

Worthy of attention, especially in areas with severe winters, are heat-protected shallow foundations that use both principles of compensation for frost heaving of the soil - increased rigidity and insulation of the foundation.

Thermal insulation of such a foundation is carried out in a lightweight version, which allows only to reduce the depth of freezing under the base of the foundation, and, consequently, the heaving force acting on the foundation.

Calculations and practice show that installation of only a vertical layer of thermal insulation to the entire height of the foundation and plinth, from the base of the foundation to the outer walls of the house, is capable significantly reduce the freezing depth soil under the foundation.

This combination allows, on the one hand, to reduce the size of the thermal insulation skirt of the foundation, and on the other, to lighten the construction of the foundation with increased rigidity, compared to the original version without thermal insulation.

Foundation - slab, slab foundation

Foundation in the form of a monolithic reinforced concrete slab under the entire area of ​​the house- another option for a shallow foundation.

The large support area can significantly reduce the specific loads on the ground. Reinforced reinforcement and high concrete consumption make slab foundations are the most expensive in private housing construction.

The foundation is a slab for a private house, due to its high cost, It is advisable to use for weak bearing capacity soil on the site.

 A slab foundation, just like other types of foundations, can be made with or without thermal insulation to protect against frost heaving of the soil.

It is necessary to distinguish slab foundation and shallow monolithic strip foundation with suspended

In the latter case, a monolithic reinforced concrete strip foundation and a monolithic reinforced concrete floor slab are poured over the ground.

In this version, monolithic reinforced concrete the floor slab does not participate in transferring the load from the weight of the building to the ground, but plays the role of a floor slab and must be designed for the standard load of the floors, have the appropriate strength and reinforcement.

The soil is actually used here only as temporary formwork when constructing a reinforced concrete floor slab. This design is often called a “suspended floor on the ground”.

Strip foundation with a monolithic suspended floor slab often mistakenly considered a slab foundation with stiffeners. The designs are really similar, but there are significant differences in details - reinforcement, dimensions.

In all cases, when constructing foundations, it is necessary to provide for water protection measures aimed at reducing soil heaving deformations - ensuring reduction of soil moisture, lowering, removal of surface water from the house via device vertical layout, drainage ditches, trays, trenches, etc.

Slightly buried foundations should Use with caution for houses on steep slopes and slopes. For foundations that are not deeply buried, the risk of shifting (sliding) is quite high due to the almost complete absence of pinching in the ground.

As you can see, choosing a fundamental design and calculating the foundation is a complex and responsible task. The final results primarily depend on a reliable assessment of the soil at the base of the building, which is quite difficult to obtain without surveys. The cost of a mistake can be very high. Independent choice of foundation can be recommended for auxiliary buildings, outbuildings and small garden houses.

It is wiser to order the design of the foundation for building a house to specialists.

Additional information on the design and use of shallow foundations can be obtained from the book of one of the authors of SNiPs V.S. Sazhin “Do not bury the foundations deep.” Download books in djvu format 389 kb. And in PDF format 4150 kb(follow the link and select “File” > “Download” from the menu at the top left).

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A strip foundation on heaving soils is a foundation that is erected during the construction of buildings that are not equipped with basements, have low weight and have a low number of storeys. The peculiarity of heaving soils is that when the water contained in them freezes, uneven deformations occur. When the temperature drops environment Below 0 0 C, the water in the ground freezes and expands, as if trying to push the foundation of the building out of the soil. The construction of a shallow strip foundation on heaving soils is justified by the fact that the resulting deformations of such a structure are not dangerous.

Selection of support

The work of building a house on heaving soil begins with the creation of a project. To do this, first of all, geological and geodetic surveys are carried out, during which the following is established:

  • groundwater level (GWL);
  • soil freezing depth;
  • features of its composition.

The research carried out will make it possible to accurately calculate the upcoming loads and select the brand of cement for preparing the concrete mixture.

Concrete grade M300 can withstand a load of 300 kg/cm2. To determine the grade of concrete that will be needed for construction, you need to calculate the total mass of the structure and divide the data obtained by the total area of ​​the base.

The peculiarity of a shallow foundation is that it is used in the construction of any buildings. This could be a residential building, a garage, a barn, a bathhouse, or a gazebo. Having arranged such a foundation, you can make an extension to the house. According to many experts, the best option the foundation of the house is the creation slab foundation on heaving soils. In the presence of heaving soil, a shallow foundation such as a monolithic slab can be built, but a shallow strip foundation is more popular.


The operating principle of this design differs significantly from the strip base. The slab can withstand various loads and negative impacts, including soil expansion with a noticeable decrease in air temperature. On soils with high levels of humidity, the soil expands noticeably on frosty days. The soil heaves, causing destruction of the improperly created foundation of the building.

How to make a foundation in an area with a high groundwater level? In most cases, builders decide to build a strip foundation on heaving soil, since the slab requires work to be performed with a large expenditure of material resources and physical effort.

Recessed foundations are subject to significant loads from the soil when temperatures drop and water in the soil freezes, if the groundwater level is insignificant and the moisture is located almost close to the surface of the earth.

Design, calculation, marking

The characteristics of heaving soil require precise calculations when designing the foundation of a building. You need to calculate:

  • trench depth for the foundation strip;
  • its width;
  • the total load that the foundation will have to withstand.

Accurate calculations, which make it possible to choose the right grade of cement for creating a concrete mixture and reinforcing bars for installing a reliable frame, are made on the basis of research, the results of which are indicated in the design documentation.

Such a characteristic as the strength of a monolithic base tape depends on the accuracy of the calculations made regarding the density of concrete. The density of concrete is determined by its grade. From an already known value, you need to subtract the volume of reinforcing bars used to create the frame, and the result of the calculation will be the volume of the concrete mixture. By multiplying the density of the foundation by its volume, you can calculate its mass.

The parameters of a shallow foundation may vary depending on the depth of immersion in the ground.

The volume of the foundation is the product of the length of the base tape, its height and width. In accordance with the project, a construction plan is developed, which is transferred to the area during the marking:

  1. From the nearest building, fence, pole, measure a distance of at least 3 m and hammer in the first peg.
  2. The first line of the outer perimeter of the future foundation will run from this peg in the desired direction, and the second peg will be driven at the distance specified in the design documentation.
  3. Having noted the length of the base tape, they begin to create a right angle using a construction angle or the so-called Egyptian triangle. On the already stretched cord connecting the first pegs, mark a point, taking a distance from any peg of at least 3 m. Then, following the indication of the construction angle, tighten the cord that determines the width of the foundation. Before finally securing the third peg, mark a point on the second cord that is arbitrarily distant from the future corner (4-5 m). Taking these values ​​as the legs of a right triangle, calculate the value of the hypotenuse, and, connecting the marked points with a segment of the calculated length, obtain a right angle at the base of the triangle. Only after this, 2 laces are pulled and 3 pegs are driven in.
  4. Similarly, the next right angle is calculated and created.
  5. Check the correctness of the marking of the outer perimeter by comparing the values ​​of the diagonals of the resulting rectangle.
  6. Now you can measure a distance equal to the width of the tape specified in the project + 10 cm for the thickness of the formwork panels, drive in pegs and pull the second string strictly parallel to the first, marking the inner perimeter of the base.

Site preparation and formwork assembly

Even before marking begins, you need to carefully prepare the site on which construction will take place:

  • get rid of excess vegetation;
  • remove the fertile layer of soil;
  • remove the garbage and make room for the assembly of the reinforcement cage;
  • Level the site using a laser level.

Make markings on a level area, after which you can begin excavation work. You need to dig trenches no deeper than 40 cm. The formwork, assembled from panels, will be above ground level, and the total height of the monolithic foundation strip is determined in the project. Backfill is made at the bottom of the trench. To create a high-quality sand cushion, take river sand and cover it with a layer of 15-20 cm. After pouring with water and compacting, this layer will become smaller, but 10 cm of compacted sand is enough to create high-quality drainage.

To build a reliable formwork structure, you need to do more than just install panels by lowering them into trenches. A wooden blank, consisting of several rows of high-strength wood, is supported from the outside with lumber, and firmly fastened on top with transverse jumpers.

During excavation work, the developed soil is tilted no less than 1.5 m from the trench. This is done in order to facilitate the removal of earth and free up space for the assembly of formwork and reinforcement cage.

Another option for using developed soil is external bedding. It is necessary when arranging a shallow foundation strip.

An important point is fixing the waterproofing, which will not allow moisture from the solution to be absorbed into the wooden panels. For this purpose, roll materials are used:

  • plastic film;
  • roofing felt;
  • roofing felt

Frame and fill

The shallowly buried strip base must be reliably reinforced, providing effective reinforcement of the structure. This requires installation of a metal frame:

  • long reinforcing bars with a ribbed surface are laid in two rows; their cross-section is from 12 to 16 mm; ribs on the surface of each product provide reliable adhesion to concrete;
  • rods with a smooth surface with a cross-section of 10-12 mm are used to create transverse bridges that provide structural rigidity.

All connections are fixed with a viscous one, which requires a special binding wire. It is not recommended to use welding, since places welds are subject to corrosion.

The reinforcement cage can be assembled both inside the formwork structure and on the soil surface. If installation is carried out next to the formwork, the finished frame is laid on the bottom of the tape, providing additional reinforcement in the corners. High-quality reliable reinforcement consists of 2 rows of 5 rods, vertical and horizontal jumpers.

Quantity longitudinal rods and the number of lintels depends on the length of the foundation. Dimensions - depending on the height and width of the tape. A shallow strip foundation is constructed on the principle of combining all components into a single horizontal frame, characterized by increased rigidity. Thanks to the sand and gravel cushion, a reliable connection with the soil is created; due to the drainage system, even wet soil does not cause destruction of the structure.

The strength of the base also depends on the quality of the concrete mixture used to fill it. The grade of cement for preparing concrete is selected depending on the load that the base will have to withstand. You can prepare concrete yourself by taking 1 part cement, 3 parts sand and 5 parts medium crushed stone.

It is important to remember that filling is done in one step. If concrete is prepared on your own, then it is necessary to observe the permissible time intervals between pouring ready-made portions of the solution. Each such period should not exceed 1.5 hours. Get more detailed information You can learn about the construction of a shallow strip foundation by watching the video.

A detailed study of the properties of the soil at the construction site makes it possible to construct a foundation protected from the negative destructive effects of ground and surface water. Shallow strip foundations for low-rise buildings are different high degree resistance to various shrinkages and soil deformations.