Foundations on heaving soils. Shallow foundations on heaving soils
Abundant soil has always been considered far from the best option for construction there. This is explained by the fact that usually in connection with this there is a need to solve a number of problems. So, for example, it will be necessary to level the winter soil movements, which pose a threat to the foundation in particular and the entire building as a whole. Based on this, experts recommend arranging an unburied base that will not be subject to uneven shrinkage. In addition, such a base is able to perfectly cope with all loads. It is best to equip a shallow foundation on heaving soils... This is exactly what will be discussed in our article.
What ways can you equip the foundation on heaving soil
Arrangement of the foundation foundation on moving types of soil is an undesirable option. This is due to the fact that there is a sufficiently large heaving force capable of lifting entire buildings. Nevertheless, the foundation can be organized on such a basis, although it is worth taking seriously the choice of its variety. In addition, you should resort to some technologies that can reduce this phenomenon.
The most reliable option would be to replace the moving soil with sand. This is done up to the freezing point. This option, although the most effective, but its cost is too high, so its use in many cases is impractical. There is also another method, which involves the use of this type of foundation, which will lie deep enough to reach the freezing point. This refers to the columnar and pile foundation on heaving soils. Heaving will not be able to act on such grounds, but here there is a significant drawback. It lies in the fact that in many cases, such foundations entail considerable costs.
But you can also resort to the third option, which consists in using a shallow foundation. Its use allows ensuring reliable stability of the building. This type of foundation is able to effectively resist ground movement. Due to its excellent strength characteristics, it is not prone to any shrinkage. In most cases, the role of such a foundation is played by a shallow strip foundation. It is made of monolithic reinforced concrete structures.
Such a foundation is installed on a sand cushion covered with a waterproofing layer. As for the walls of the trench, they can be reliably protected using specialized materials. In the process of mixing it, experts recommend adding a hydrophobic composition to the concrete mixture that can improve the stability of the structure. After completing the construction of the base, care should be taken to create a drainage system. We also do not forget about the reinforcement when arranging the foundation.
Varieties of bases for mobile soil
In progress construction works on mobile soil types, not all types of foundations can be used. The best option in such a situation is a shallow foundation for the house. It is able to effectively resist the processes of soil heaving, which prevail in the cold season. If you look at the choice of shallow foundation foundations for moving types of soil, then the strip foundation has won the greatest popularity. It has a number of advantages, among which the main ones are the following:
- LF-base is able to provide the required durability and reliability of the structure;
- The construction of such a foundation is characterized by lightness and simplicity;
- Relatively low construction cost.
We also note other types of foundations that can be used on moving ground. This includes a pile foundation, but at present it is not very popular. This is explained by the fact that for the purpose of its construction, the use of specialized equipment may be required, which entails an increase in the cost of construction in general. This option can be used in cases where the level of soil freezing is at a depth of at least 1.5 meters.
In the process of production of support-pile structures, various materials are used to resist heaving processes. This includes concrete, reinforced concrete elements, as well as wood. It is also imperative to equip a reliable drainage system.
A shallow columnar foundation is also used. Its use is relevant in cases where the supports can be installed below the level of soil freezing. Thanks to this, the financial costs for the arrangement of the foundation are somewhat reduced. At the same time, excellent reliability still exists.
The foundation foundation of the columnar type is used subject to the presence of loam, soil with the nearest occurrence of groundwater, as well as in swampy areas. For the purpose of arranging a base of this type on moving soils, reinforced concrete support pillars and steel pipes with a sand-cement protective composition are most often used. In addition, pipes made of asbestos cement can also be used, they are filled with concrete mortar.
Shallow tape base
A strip foundation on heaving soils is essentially a monolithic concrete strip. It is equipped with a reinforcing belt, which uses steel rods. For the correct installation of such a foundation, several steps should be performed, each of which we will consider below.
The initial steps here are approximately the same as when erecting a standard foundation foundation. It is necessary to dig a pit about half a meter deep. Next, you should start laying the waterproofing layer on the side slopes. Its role is played by a plastic film or roofing paper.
The design of foundations on heaving soils provides for the arrangement of a sand cushion at the bottom of the pit. It consists of several layers of sand twenty centimeters thick. After each of the layers is filled up, it is necessary to carefully tamp it. Then a formwork structure is arranged from the board. A waterproofing layer should be laid on top of the sand cushion, reinforcing steel rods with a diameter of 12 centimeters should be placed.
As part of the next, final stage, it is necessary to fill the shallow foundation on heaving soils with concrete mortar. The upper reinforcement layer is installed on the green mix. In the process of combining reinforcing components, you should abandon the use of a welding machine. The technology involves the use of knitting wire.
Shrinkage of buildings on mobile soils
The construction of structures on heaving soil types threatens with possible shrinkage, as well as deformation processes directed against the foundation. Commonly encountered are the following:
- Deflections and kinks due to uneven shrinkage. In this case, the bends are much more dangerous, since they can affect the condition of the roof.
- Shifts. The device of the foundation on heaving soils can threaten shifts caused by the rise of one side of the building and the rise of the other.
- Distortions are formed due to uneven shrinkage in some places under the structure.
Many people ask questions about why such uneven shrinkage occurs. This phenomenon is due to the fact that as a result of freezing of the soil, the moisture that it contains also freezes. And this, in turn, leads to an increase in its volume. As a result, the soil swells. Further, whole layers of soil can rise, which leads to deformation and destruction of the building.
These processes negatively affect the erected building only if it was built without taking into account the characteristics of the soil. Therefore, you should carry out the device of shallow foundations. As we already indicated in the article, except strip base shallow depths can also be used for pile and post foundations. The main thing is to strictly observe the technology, and destructive processes will not affect your building.
When choosing (if possible) a plot for building a house, the owner often ignores the properties of the soil, and this is an important component when deciding on the type of foundation for a building. And, if the site is rich in moisture or loose materials, then the soil is likely to swell in the demi-season and in winter. At the borders of winter-spring and autumn-winter, the soil can swell from an excess of groundwater, and a feast of negative temperatures - from the expansion of water, turning into ice. Therefore, a solid foundation for any home is a shallow strip foundation on heaving soils, which, due to its construction, simply ignores the pressure of the soil and ice.
MZLF in action
Construction work on the construction of a shallow foundation for a house on a heaving plot has a more extended list, but it is necessary to protect the house and foundation from destruction or flooding. Since the buried walls of the concrete tape are at a depth of no more than 0.5-0.7 m, the heaving forces that manifest themselves at the level of freezing of the soil do not act on it, however, there remains the danger of oversaturation of the building materials of the base and walls of the house with moisture. Therefore, additional waterproofing and thermal insulation of the tape must be provided.
If on a site with heaving soil it is planned to build a heavy house made of concrete or slabs, then it is better to replace the layer of heaving soil. These are huge volumes earthworks, but otherwise the foundation may not withstand the counter loads - both from the weight of the house from above and from the heaving forces from below. In this case, the MLF turns out to be ineffective, and optimal design there will be a columnar or pile foundation.
If it is impossible to equip a house on another basis, the MZLF is carefully calculated, reinforced, protected from any negative influences on it, and building materials for the house are selected in order to reduce the total mass of the structure. It can be aerated concrete (foam or gas blocks), wood, or at least hollow.
![](https://i1.wp.com/rfund.ru/wp-content/uploads/2017/09/2-2.jpg)
From the diagram above, it can be seen that MZLF relies on, protected by waterproofing materials (roofing material, bitumen, membrane), the sides of the trench must also be protected with waterproofing. Hydrophobic additives in the concrete solution will provide it with greater strength and resistance to moisture absorption. Additionally, such a foundation is protected by drainage and stormwater systems built around the house, as well as by a durable waterproof blind area with insulation. Reinforcement of the tape is carried out with reinforcement, that is, the reinforcement in the MZLF should be 30-50% more than in a conventional reinforced concrete foundation.
Shallow or shallow basement options
On a site with heaving soil, not every type of foundation will work reliably, but an unburied or shallow foundation is a solution that is optimal in all operational parameters. A columnar or pile foundation can be shallow, but the strip foundation is the most reliable, since the load is distributed literally by millimeters over the entire area of \u200b\u200bthe belt. In terms of cost, it is cheaper than many other structures, since earthmoving does not take large amounts of estimates, less concrete and waterproofing materials are needed for it.
![](https://i2.wp.com/rfund.ru/wp-content/uploads/2017/09/3-2.jpg)
The pile foundation with a grillage also belongs to the MZLF. Suitable for him are steel pipes, which are covered with liquid cement-sand mortar for protection, reinforced concrete pillars, asbestos-cement pipes, etc.
Construction and arrangement of MZLF
When building a standard shallow strip foundation on heaving soil, only concrete, reinforcement and waterproofing are needed. MZLF on difficult ground is a monolithic concrete tape, reinforced with a frame made of iron rods.
The first step in the implementation of MZLF is digging a trench under it up to 0.7 m deep. The sides of the trench are closed with waterproofing - roofing felt or even ordinary polyethylene. After arranging a sand cushion up to 0.3 m thick, a plank formwork is assembled in the trench. The bottom of the sand cushion is also waterproofed, and a reinforcing frame is assembled in the formwork. The structure can also be tied on the surface, if there are enough working hands, then lower the frame into the trench on plastic substrates.
The reinforcement frame is tied from rods Ø 12-16 mm, has two horizontal belts, tied with vertical transverse rods every 0.5-0.7 m. The frequency of rods in the horizontal belt is up to 5 pieces. The frame must be at least 5 cm away from all nearby surfaces (top, bottom, sides) so that all rods are immersed in concrete in order to prevent metal corrosion. It is strictly forbidden to use welding when assembling the reinforcing frame.
![](https://i1.wp.com/rfund.ru/wp-content/uploads/2017/09/4-2.jpg)
Uneven shrinkage of the foundation on heaving soil
Shrinkage is possible and inevitable even on dense rocky ground, not to mention heaving layers. Common deformation phenomena from soil shrinkage:
- Bending of the foundation inward or outward: Most often caused by uneven shrinkage. Bending upwards is more dangerous, as it affects the strength of the rafter system and roof;
- Lateral shifts: if one part of the tape has subsided, and the other has risen, then the object may move to the side. The zone in the middle of this segment is the most dangerous;
- Tilting of a building can occur if the object is high and the foundation is not buried or shallow;
- The house is distorted: these are the consequences of uneven shrinkage of local sections of the base;
- Horizontal displacement: Displacement of local areas at the foundation during soil heaving.
To minimize or completely level possible shrinkage and consequences in heaving areas, it is advisable to use lightweight building materials: aerated concrete, wood, hollow brick, expanded clay blocks.
![](https://i0.wp.com/rfund.ru/wp-content/uploads/2017/09/5-2.jpg)
Calculation of MZLF
Consider a real example of calculating the MZLF on an area with heaving soil for a house with dimensions: wall height - 3.5 m, building width - 6 m, house length - 12 m. The main loads are perceived by two load-bearing walls, each with a height and length of 3.5 m The concrete floor is set on beams. Reinforced concrete tape (Ø rods - 12 mm) foundation has a width of 0.5 m, depth - 0.6 m. The armored frame consists of two rows of 5 rods in each row, reinforced with transverse rods 0.25 m long with a step of 0.5 m.
To calculate the weight of the tape, you need to know the dimensions of the house and the density of the building materials. We calculate the dimensions of the house by summing the lengths of all sides (including the lengths of the internal walls): 3.5 + 3.5 + 6 + 6 + 12 + 12 \u003d 42 meters.
We are looking for the volume of the tape, knowing its dimensions (0.5 mx 0.6 m):
V \u003d 42 x 0.5 x 0.6 \u003d 12.6 m 3.
We found the total volume of the foundation, and from this value it is necessary to subtract the volume of reinforcement in order to find out the exact volume of concrete solution. Our armopoyas is connected in 2 rows with 5 rods in each row, rods Ø - 12 mm. Length of each row: 12 - 0.5 - 0.5 \u003d 11 m.
The total length of the reinforcing belts: 2 x (11 x 2 + 3.5 x 2 + 3 x 2) \u003d 70 m. Considering that there are 5 rods, the total length of the reinforcement is 70 x 5 \u003d 350 m.
![](https://i2.wp.com/rfund.ru/wp-content/uploads/2017/09/6-2.jpg)
Find out the length of the transverse jumpers:
- 11 / 0.5 + 1 \u003d 23 pieces;
- 3.5 / 0.5 + 1 \u003d 8 pieces;
- 3 / 0.5 + 1 \u003d 7 pieces.
For one row of jumpers you need: 23 × 2 + 8 × 2 + 7 × 2 \u003d 76 pieces;
With a lintel length of 0.25 m, their total length is: 76 x 0.25 \u003d 19 m.
Since the frame consists of two rows, the total reinforcement for the lintels will need twice as much - 38 meters. Vertical lintels are installed on both sides of the reinforcing frame, so their total number will be: 76 x 2 \u003d 152 pieces with a single lintel length of 0.4 m and a total length of reinforcement: 152 x 0.4 \u003d 60.8 m.
The calculation of the section of the reinforcing rods is carried out using the formula for the area of \u200b\u200ba circle: ∏ x 0.000036 \u003d 0.00011304 m 2.
The volume of one reinforcing bar Ø 12 mm is calculated by the formula: 0.00011304 x 448.8 \u003d 0.0507 m 3.
The total volume of concrete without reinforcement is: 12 - 0.04 - 0.04 \u003d 11.92 m 3, where 0.04 is the coefficient applied to the reinforcement of the corners of the tape.
![](https://i1.wp.com/rfund.ru/wp-content/uploads/2017/09/7-1.jpg)
Thus, the final results of calculations of materials for a strip shallow foundation will be as follows:
- 12.6 m 3 of concrete with a density of 2.5 t / m 3;
- 0.08 m 3 reinforcing bars with a density of 7.8 t / m 3.
Total foundation weight:
- 12.6 m 3 x 2.5 t / m 3 \u003d 31.5 tons;
- 0.08 m 3 x 7.8 t / m 3 \u003d 624 kg;
- 31500 + 624 \u003d 32.124 tons.
A private house on a site with heaving soil is not the best option, but often you do not have to choose, and from the results of calculations it becomes clear that MZLF is best suited for this purpose. All that is required from the developer is to accurately calculate the parameters of a shallow foundation, since the slightest error or inaccuracy in the calculations will lead to the fact that the foundation will be pushed out of the ground during seasonal or winter, and with it the building itself will be deformed.
Shallow strip foundation on heaving soils updated: February 26, 2018 by: zoomfund
It is impossible to call heaving soil the best option for building a foundation. To prevent the foundation from collapsing on such soil, it is necessary to solve several problems and adhere to some rules. After all, ground movements are fraught with the fact that the foundation can deform and a crack forms on the building. According to many experts, a shallow strip foundation on heaving soils is an ideal solution. It will handle the load perfectly without fear of uneven shrinkage and destruction.
In addition, this design will fit most buildings. And what are the other advantages of a shallow foundation? And what can you do? What should be considered during construction? How exactly is it to be built? Let's find out.
Description of the foundation and its positive aspects
A shallow strip foundation is the middle option between a shallow and a buried strip foundation. The construction technology is almost identical to the conventional foundation. Only the depth of the tape is changing. However, this allows the foundation to be "maneuverable" and when the soil heaves up, it can rise with it. At the same time, it will not collapse. Just to achieve this, when laying the foundation, you must strictly adhere to the technology. If you deviate from the rules, then your home foundation can crack.
There are many benefits to the tape being shallow. What are they?
- The ability to do all the work with your own hands.
- The work does not require the involvement of heavy equipment. Enough of banal tools and hands.
- Since less material is required, the cost of work is also reduced.
- The device of a shallow strip foundations is much faster.
- Labor costs for the formation of a foundation on heaving soil are reduced.
- It has good load bearing capacity and is suitable for small houses, summer cottages, garages and baths.
For small house with heaving soil - this is the ideal base. The prime cost is less than that of a deep foundation, and the bearing capacity is sufficient for construction.
Note! It is impossible to lay a shallow foundation in the winter period when the soil is frozen. And for the winter, leaving it unloaded is also prohibited.
As for the period for which you can pour the foundation and erect the walls, it is approximately 4-5 months. And from what can the base be made?
Foundation materials
We learned that a strip foundation consists of a strip that runs shallow in the ground and runs under each wall. In the classic version - this tape is made monolithic. But this option is not the only one. There are other materials that are suitable for this job. What are they?
Reinforced concrete foundation
The most common and demanded base option. Differs in high strength of the finished foundation. Thanks to the concrete solution, the tape is monolithic, without seams and cold bridges. And to strengthen the concrete and give it more rigidity, reinforcing bars are used. This reinforced mesh allows the concrete not to crack and to be more durable.
Concrete foundation
Rubble concrete is practically the same concrete, only when it is made large rubble stones are added to the solution. However, if we consider that we are talking about heaving soil, then it is not suitable for this purpose. It can be used on light soil such as sand, rocky and gravel.
Brick foundation
The option is expensive, therefore it is rarely used. It is permissible to erect such a foundation only for regions with a dry climate, in which there is practically no groundwater and a minimum amount of precipitation.
Foundation calculation parameters
Everyone knows that before starting the construction of any foundation, you need to perform calculations and draw up a plan. What should be considered when found on heaving soil? It is important to analyze the degree of heaving of the soil. The second point is the bearing capacity of the soil. Depending on this, the thickness of the sand cushion, the height and width of the foundation tape are determined. Some are guided by this formula: to determine the depth, the width of the tape is multiplied by 3-4 times.
Pay attention! The area of \u200b\u200bthe building and the presence of additional floors are also important.
When calculating, take into account basements or semi-basements. And to speed up the preparation before construction and the work itself, indicate the material that you will use and its amount. The size of the base (above ground) should not exceed the underground section of the tape. Less is possible, but no more. Usually, a shallow foundation has a depth of about 50 cm.
I would like to dwell in more detail at the depth of the foundation. In addition to everything, it also depends on the depth of soil freezing and the level of groundwater. The principle is this - if the groundwater is close to the surface, and the level of freezing of the soil is large, then the soil will move strongly. Therefore, you need to lay the foundation deeper into the ground. Below is a table of the minimum placement depth that you can use for your calculations.
We build the foundation with our own hands
We mentioned that such a design is appreciated because all work on the device can be done by hand. When you have made the calculation and you have a plan in hand, you can start working. Only there is one moment: it is better to start building in early spring. So, you can give the base to gain strength until the summer. And in the summer you can safely build a box. When everything is ready, you can start work. We will go through the whole process step by step, as in the instructions, so that it is easier for you to understand what is going on.
Reducing the depth of the foundations allows in some cases to save significant funds. The device of a foundation slab without deepening allows you to kill two birds with one stone - not to get involved with digging a foundation pit and erecting the underground part of the walls, and also to get a solid foundation for arranging the floor of the first floor.
But, if everything is so good, why have not the shallow foundations displaced the "usual" ones?
Why bury foundations at all?
In the classical case, the depth of the foundations corresponds to the depth of soil freezing. Follow the link: - you can download a calculator for calculating the depth of freezing of soils (cities of Russia and the CIS) with climatic maps for free. In this case, the penetration of cold into the underground of the first floor is sharply limited, the heaving effect of the soil on the base of the foundation is excluded. Recall that frost heaving is the property of water-saturated finely dispersed (clay, loamy) soils to swell when frozen.
Obviously, for the construction of a shallow foundation, it is necessary to solve two issues: leveling the forces of frost heaving, insulation.
Leveling the forces of frost heaving
In the case of the presence of heaving soil properties at the construction site for the construction of a shallow foundation, it is usually recommended to add a non-heaving material that insulates the foundations. These recommendations are described in detail in VSN 29-85 "Design of shallow foundations of low-rise rural buildings on heaving soils".
The foundation should be insulated over its entire surface, that is, not only from below, but also along the vertical edges.
It is best to use coarse or medium-grained sand as a non-porous soil. In the conditions of the seasonal appearance of the so-called "top water" (groundwater wedging out to the surface), a drainage device will be required around the building to avoid silting up the anti-powder bedding. Otherwise, after several seasons, the bedding can acquire heaving properties.
Insulation of the foundation and blind area
Insulation of a shallow foundation is critical. Warming will allow not only to avoid the penetration of cold from under the floor, but also to exclude the cause of heaving. The latter is not possible at positive temperatures.
The boundary depth of soil freezing is determined not only by the temperature of the coldest five-day period in the construction region, but also by the presence of molten magma in the center of the planet. In the absence of heat deep underground, the seasonal freezing of the soil would be much stronger, up to the impossibility of the emergence of life on Earth. This circumstance determines the direct expediency of insulating the blind area around the building - it will not allow the soil around the shallow foundation to freeze and penetrate under it.
1-monolithic foundation, 2-wall masonry, 3-base of the floor, 4-sand bedding, 5-insulation, 6-waterproofing, 7-backfilling, 8-blind area.
In this case, only hydrophobic materials that do not absorb moisture and have high strength indicators are allowed as insulation. The best choice of common materials is EPS - extruded polystyrene foam, often referred to as "hard foam". It can even be laid under the foundation slabs of light buildings.
Floor insulation and temperature conditions
The main difficulty in constructing shallow foundations is finding a balance between floor insulation and temperature conditions in winter. This is critical for cold regions with a basement.
When constructing a shallow foundation, it is necessary to exclude soil freezing not only under the foundation, but also under the floor.
Very often there is an opinion that when insulating the blind area and vertical edges of the underground part of the building, floor insulation can be omitted, or performed with a small thickness. Allegedly, a soil massif, having absorbed the heat under the building, itself performs the function of a heater. But let's imagine a situation when, for some reason, a newly built house is not put into operation in the first winter season. In the absence of full-fledged insulation under the floor and with the heating turned off, freezing can occur, since the only source of heat will be deep underground. Insulated walls, ceilings and a roof, due to the lack of tightness of the building, can hardly guarantee a positive temperature in the room during severe frost outside. Visiting in winter country house with the heating turned off, you don't expect a positive temperature inside, do you?
Thus, the main danger for a building with a shallow foundation is freezing through the outer walls of the building. In order to avoid heaving of the soil under the floor, it is necessary either to provide a positive temperature in the rooms in winter, or to provide floor insulation with the same thermal resistance that is required for walls in the construction region. Moreover, the second option, perhaps, is preferable - the energy consumption for heating the soil mass under the building will decrease, in winter, in the absence of heating, the soil temperature under the building will be uniform. With "partial" floor insulation while maintaining a positive temperature, freezing is possible in the corners of the building, as in the most vulnerable zone.
Swedish experience
In support of the above, consider the temperature diagrams from the report of Swedish specialists who studied the experience of building private houses on unburied slabs in Sweden itself. A region with a freezing depth of 2.3 m was considered. Studies were carried out with a thickness of insulation in the floor of 10cm, 20cm and 30cm. As a result, the following temperature diagrams were obtained:
As can be seen from the figure, in the absence of an insulated blind area with a large thickness of insulation, the thermal regime of the building cannot completely warm up the soil mass. Freezing of the soil goes under the stain of the building. Powerful floor insulation (in terms of heat conservation inside the ground) does not save the corners of the building from frost on the surface. Conversely, with a slight insulation of the floor in the case of switched on heating, freezing due to significant energy consumption for heating does not occur.
Consider the following diagram:
In this experiment, 0.3 m thick insulation was laid under the building stain, and 0.1 m thick under the blind area. The width of the insulation of the blind area was taken equal to 0m, 0.6m, 1.2m. The resulting diagram clearly shows the effectiveness of the insulation of the blind area. With a width of insulation of 0.6 m and 1.2 m, all other things being equal (in relation to the previous experiment), soil freezing does not go under the stain of the building.
In our country, the spread of shallow foundations is only beginning to be used en masse due to the lack of experience in such construction. To date, there are no requirements for the construction of insulated foundations in the regulatory building documents.
So what's the bottom line? How to properly arrange an unburied foundation?
The device of shallow foundations can be divided into two categories - by isolating the foundation from heaving forces, by eliminating heaving by means of insulation. Let's summarize briefly for each option.
Isolation with sand bedding is a solution of the last century. Solving the issue of the effect of heaving forces on the foundations does not resolve the issue of energy consumption for heating the freezing floor. The use of bedding made of drainage material (crushed stone, gravel) is advisable in case of difficult hydrogeological conditions (seasonal top water) in combination with water disposal. At a relatively deep water table, the use of non-heaving soils as a base can be recommended for highly and excessively heaving soils. With moderate heaving, it is permissible to support the foundation on the root soil, subject to complete (see below) insulation. In this case, it is advisable to backfill the sinuses of the trenches (foundation pit) with non-porous soil in order to reduce the risk of deformation of the blind area.
Modern hydrophobic heat-insulating materials with high strength indicators make it possible to build shallow foundations on heaving soils. In order to avoid the risk of deformation of the corners of the building, as well as freezing of the underground massif of soil in the event that the object is not put into operation in the winter, it is necessary to carry out full insulation of the basement of the building. The entire floor area, directly the foundations (if it comes not about the slab), the basement of the walls and the blind area must be inseparably insulated. The thermal resistance R of such insulation must be identical to the requirements for walls in the construction region. The width of the insulation of the blind area can be taken equal to at least the depth of freezing. With a significant level of heaving properties of the indigenous soil - 1.5 depth of freezing (desirable).
The experience of construction in Sweden, Finland, Greenland and not only determines the admissibility of the installation of practically unburied foundation slabs for light houses. For this, the vegetation layer is cut, the construction site is leveled with sand filling, a rigid hydrophobic insulation (extruded polystyrene foam) is laid under the entire stain of the building, and the blind area is insulated along the entire perimeter of the building.
In the case of construction on a shallow foundation of a light house made of gas blocks, the correct
A strip foundation on heaving soils is a foundation that is erected during the construction of buildings that are not equipped with basements, have a low weight and low number of storeys. The peculiarity of heaving soils is that when the water contained in them freezes, uneven deformations occur. When the ambient temperature drops below 0 0 C, the water in the soil freezes, expands, as if trying to push the foundation of the building out of the soil. Arrangement of a shallow strip foundation on heaving soils is justified by the fact that the resulting deformations are not terrible for such a structure.
Support selection
The work on building a house on heaving ground begins with the creation of a project. For this, first of all, geological and geodetic surveys are carried out, during which it is established:
- groundwater level (GWL);
- depth of soil freezing;
- features of its composition.
The research carried out will allow you to accurately calculate the forthcoming loads and select the brand of cement for preparation concrete mix.
M300 concrete is capable of withstanding a load of 300 kg / cm 2. 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 by total area grounds.
The peculiarity of a shallow foundation is that it is used in the construction of any buildings. This can be a residential building, garage, barn, bathhouse, gazebo. Having equipped such a base, you can make an extension to the house. According to many experts, the best option for the foundation of a house is to create a slab foundation on heaving soils. In the presence of heaving soil, such a shallow foundation as a monolithic slab can be built, but a shallow strip foundation is more popular.
![](https://i0.wp.com/kakfundament.ru/wp-content/uploads/2017/08/1-185.jpg)
The principle of operation of this design is significantly different from the tape base. The slab is able to withstand various loads and negative influences, including the expansion of the soil with a noticeable drop in air temperature. On soils with a high level of humidity, the earth expands noticeably on frosty days. The soil swells, causing destruction of the improperly created base of the building.
How to make a foundation in an area with a high groundwater level? In most cases, builders decide on the construction of a strip base on heaving soil, since the slab requires work with a large expenditure of material resources and physical effort.
Recessed foundations are subjected to significant loads from the soil when temperatures drop and water freezes in the soil, if the GWL is insignificant, and moisture is practically close to the ground surface.
Design, calculation, markup
The features of heaving soil require accurate calculations during the design of the base of the building. You need to calculate:
- the depth of the trench for the foundation tape;
- its width;
- the total load that the foundation has to withstand.
![](https://i2.wp.com/kakfundament.ru/wp-content/uploads/2017/08/1-186.jpg)
Accurate calculations, which make it possible to choose the right brand of cement for creating a concrete mixture and reinforcing rods for installing a reliable frame, are made on the basis of studies, the results of which are indicated in the project documentation.
Such a characteristic as the strength of a monolithic base tape depends on the accuracy of the calculations made in relation to the concrete density. The density of concrete is determined by its grade. From the already known value, you need to subtract the volume of the 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 can 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:
- From the nearest building, fence, pillar, measure a distance of at least 3 m and hammer the first peg.
- 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 hammered at the distance specified in the design documentation.
- Having noted the length of the base tape, they begin to create a right angle using a building angle or the so-called Egyptian triangle. On the already stretched lace connecting the first pegs, mark a point, taking a distance from any peg not less than 3 m. Then, following the indication of the building angle, pull the lace, which determines the width of the foundation. Before finally fixing the third peg, a point (4-5 m) arbitrarily removed from the future corner is marked on the second lace. Taking these values \u200b\u200bfor the legs of a right-angled triangle, calculate the value of the hypotenuse, and by connecting the marked points with a segment of the calculated length, a right angle is obtained at the base of the triangle. Only after that 2 laces are pulled and 3 pegs are hammered.
- Similarly, the next right angle is calculated and created.
- The correctness of the marking of the outer perimeter is checked by comparing the values \u200b\u200bof the diagonals of the resulting rectangle.
- Now you can measure a distance equal to the width of the tape specified in the project + 10 cm for the thickness of the boards of the formwork structure, drive in the pegs and, strictly parallel to the first lace, pull the second, marking the inner perimeter of the base.
Site preparation and formwork assembly
Even before the start of the marking, you need to carefully prepare the site on which the construction will be carried out:
- get rid of excess vegetation;
- remove the fertile soil layer;
- take out the debris and make room for the assembly of the reinforcing cage;
- level the platform using a laser level.
On a flat area, markup, after the completion of which you can start performing land work. It is necessary to dig trenches no deeper than 40 cm. The formwork assembled from the panels will be above ground level, and the total height of the monolithic foundation tape is determined in the project. Backfilling is done at the bottom of the trench. To create a high-quality sand cushion, they take river sand, fill it with a layer of 15-20 cm. After pouring water and tamping, this layer will become smaller, but 10 cm of compacted sand is quite enough to create high-quality drainage.
To build a reliable formwork structure, you need to do more than just install the panels by lowering them into the trenches. A wooden blank, consisting of several rows of high-strength wood, is propped up from the outside with sawn timber, and from above is firmly fastened with transverse bridges.
![](https://i0.wp.com/kakfundament.ru/wp-content/uploads/2017/08/1-187.jpg)
In the course of the excavation work, the developed soil is tilted at least 1.5 m from the trench. This is done in order to facilitate the removal of the earth and make room for the assembly of the formwork and reinforcement cage.
Another option for using the developed soil is external bedding. It is necessary when arranging a shallow foundation tape.
An important point is the fixing of waterproofing, which will not allow moisture from the solution to be absorbed into wooden shields. For this, roll materials are used:
- plastic wrap;
- roofing material;
- roofing paper.
Wireframe and fill
The shallow tape base must be reliably reinforced, providing effective reinforcement of the structure. This requires the 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 ensure 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.
The fixation of all joints is carried out with a knot, which requires a special knitting wire. It is not recommended to use welding, as the welded seams are subject to corrosion.
![](https://i1.wp.com/kakfundament.ru/wp-content/uploads/2017/08/1-188.jpg)
Reinforcement cage can be collected both inside the formwork structure and on the soil surface. If the installation is carried out next to the formwork, the finished frame is laid on the bottom of the tape, performing additional reinforcement in the corners. High-quality reliable reinforcement consists of 2 rows of 5 rods, vertical and horizontal lintels.
The number of longitudinal rods and the number of lintels depends on the length of the foundation. Dimensions - from the height and width of the tape. A shallow strip foundation is built 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 drainage system even wet earth does not cause structural failure.
The strength of the base also depends on the quality of the concrete mixture used for pouring it. The brand of cement for concrete preparation is selected depending on the load that the base has to withstand. You can prepare concrete yourself by taking 1 part of cement, 3 parts of sand and 5 parts of medium-fraction crushed stone.
It is important to remember that filling is done in one step. If the concrete is prepared on its own, then it is necessary to observe the permissible time intervals between pouring ready-made portions of the solution. Each such interval should not exceed 1.5 hours. You can get more detailed information on the construction of a shallow tape base by watching the video.
A detailed study of soil properties at the construction site allows you to build a foundation that is protected from the negative destructive effects of ground and surface waters. The shallow strip foundation for low-rise buildings is distinguished by a high degree of resistance to various shrinkage and soil deformations.
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