Arriving after winter at the summer cottage, take a close look around. And you will see that in some houses, cracks snake on the walls and glass of windows. In other areas, the gate sloped (Figure 1), the woodshed or shed leaned heavily (Figure 2).
This is the result of the action of such an extremely undesirable natural phenomenon as soil swelling. Especially badly, more precisely destructively, heaving affects, first of all, that part of the foundations of buildings that is in the ground. This phenomenon is often not taken into account not only by self-builders, but sometimes also by professional builders.
Where does this malignant heaving of the soil come from and how is it formed? As you know from a school physics textbook, water in the process of freezing increases in volume by 10-15 percent. Because of this, the rise and fall of the soil in the Northwest reaches 20 centimeters or more.
If the expansion of water occurs in moist, dense clays, in fine sandy and dusty soils, which are capable of dramatically changing the volume and deforming (that is, swelling) at negative temperatures, then these soils are considered heaving. And coarse-grained and gravel - non-porous. Under the indispensable condition that they have a free outflow of water.
What are the processes occurring in them that make it possible to divide all soil soils into these categories? In heaving soils, moisture rises high enough from the groundwater level and, accumulating, is well retained in soils such as in a sponge.
In non-porous soils, moisture settles under its own weight, as if falling through, as if through a sieve, and therefore does not rise high. In other words: the finer (thinner) the structure of the soil, the higher the moisture rises along it, and the more it becomes heaving.
It is clear that soil freezing occurs from top to bottom. The moisture in the upper layers, turning into ice, increases in volume and goes down. And if it, without lingering, seeps through the structure of the surrounding soil, for example, through gravel, coarse sand, which practically do not create resistance, then the soil does not expand without moisture, which means that the heaving effect does not occur. And vice versa...
This is especially true for dense clay. From such clay, moisture not only does not have time to leave, but also accumulates. As a result, such soil will certainly become heaving. Heaving phenomena are not only significant completely unpredictable ground movements, but also colossal loads on the foundation, reaching a pressure of 6-10 tons per square meter.
Hence the immutable conclusion: before starting construction, it is imperative to find out what is the maximum freezing depth in a given place:
In the Leningrad Region, the freezing depth is up to 1.5 meters. It is clear that the simultaneous combination of all these factors is unlikely, but this is a safety event that allows you to predict and, therefore, avoid any natural disasters.
It is also essential that even if heaving, deforming the soil, does not directly affect the base of the foundation located below the freezing level, the stress at the border of the freezing zone can be so significant that it can squeeze out the foundation along with the frozen soil or tear off its upper part from the bottom. Such cases are most likely when constructing a foundation made of stone, brick or small blocks, especially under light buildings and structures.
This is the result of the action of the so-called lateral grip forces. They arise when frozen soil adheres to the side walls of the foundation and, under certain conditions, reach a pressure of 5 to 7 tons per square meter of the side surface.
For example, on a foundation pillar with a diameter of 20 centimeters with a freezing depth of 150 centimeters, lateral adhesion forces of more than 9 tons are affected. This is several times higher than the load from the weight of the building. And so there is a heaving effect.
This is due to the fact that above the surface there is a constant collision of the cold above and the heat of the earth. If the heat of the earth is generally constant, then the degree of soil freezing depends on many factors: temperature and humidity of the surrounding air, soil moisture, density and thickness of snow, the degree of warming up by the sun.
Due to the temperature difference, the freezing line during the day is higher than at night. This difference increases especially where there is little or no snow cover. Closer to spring, the soil on the south side thaws faster than on the north, and therefore becomes wet, and, accordingly, the snow layer above it becomes thinner than on the north side.
Therefore, unlike the northern side of the house, the soil on the southern side warms up more intensively during the day and freezes more at night, thereby contributing to the emergence of lateral adhesion forces. The effect of these forces is especially enhanced if the surface of the foundation is uneven and does not have an appropriate waterproofing coating.
Recessed strip foundations can also be lifted by lateral forces if, again, it does not have a smooth, sliding side surface and is not sufficiently pressed down from above by a house or concrete slabs.
How can we avoid such dangerous destructive and often just catastrophic troubles? One of these options, which allows you to avoid them, is shown in (Figure 3.) As we can see, there are no supports buried in the ground, which could be subjected to heaving loads. In this case, the building rests on base plates. They are pressed by a force equal to part of the weight of the building, that is, a very small load.
The coarse sand (anti-rock) cushion will prevent ice from forming and will ensure its balance. Such foundation slabs can be made at home (suburban) conditions from concrete with the addition of gravel, laying metal reinforcement. It is best to use wire. The thickness of the slab must be at least 10 centimeters. Ready-made slabs can also be used. Before laying the slabs, the sand is moistened and tamped.
However, the so-called shallow foundations are much more widespread in summer cottage construction. This is when the depth of the foundation does not reach the depth of soil freezing (Figure 4). It is clear from the law of physics that the weight of a part of a building (VZ) must be balanced by the soil heaving force (GH) generated by the expansion of the freezing soil (ice) and lateral adhesion forces (BS), which push out the supports.
The force of heaving of the soil at low temperatures can significantly exceed the weight of the building, and then the foundation support will inevitably be pushed out. This is very noticeable in early spring, when the topsoil thaws completely and warms up well. In warm weather, the support will drop, but not by much, since the space under it is filled with water and flooded soil. Such support will shift after a while, and the building will inevitably be distorted.
To avoid such an undesirable phenomenon, very often metal reinforcement is laid in the foundation and walls, and reinforcement belts are also constructed (Figure 5). Or, the base of the foundation is made expanded in the form of a support platform-anchor (Figure 6). In these cases, the stiffness of the walls and foundation increases, and, consequently, the resistance of the entire structure to loads from soil swelling increases sharply.
To be continued
Alexander Nosov, jack of all trades
What a monolithic cake looks like and its structure can be seen in the figure. (Fig. 1)
Figure 1. The device of a monolithic pie.
The options for insulation were discussed above, now let's dwell in more detail on the choice and method of making concrete.
The requirements to be met by the concrete used for concreting the slab are as follows:
If the groundwater is high enough, sulfate-resistant concrete can be used. But it can be very problematic to find it on sale.
Installation diagram of a monolithic slab under the gazebo.
Conventional fittings are suitable for a slab-type monolithic foundation. The method of fastening such reinforcement in the frame will influence the choice of its class. For fastening with ordinary knitting wire, you can use absolutely any class of fittings.
If electric welding will take part in the construction of the frame, then it is better to take reinforcement of class a 500 or similar, having the symbol C, which is placed after the number relative to the class. Types of steel reinforcement designed specifically for welding are marked in a similar way.
It is advisable to use bituminous polymer materials for the purpose of waterproofing a monolithic base plate. However, it is permissible to use any roll material for waterproofing.
By admin Published December 11, 2012 Updated February 26, 2013
Foundation - has nothing to do with aesthetics, design, style. And the thing is almost invisible to the eye. This is why future homeowners sometimes pay so little attention to it. But in vain ... The cost of building a foundation is 15-20% of the total cost of building a project (in the presence of a basement or basement floor - up to 30%), and the cost of reworking violations of the zero cycle, even insignificant at first glance, may eventually exceed any conceivable percentage. So what do you need to know?
[box]Soils, water and frost ("National characteristics") [/ box]
The main thing is to adapt the project to local conditions, namely, geology and climate. We are overcome by cold weather, difficult soils and high groundwater. The most reliable and durable - rocky - soil, which practically does not require deepening, is not found in Belarus. The bulk of this is sedimentary soils, requiring a burial of about 1.5 m. These are open spaces of all sorts of sandy loam, loam, clay, not to mention swampy areas, where one cannot do without spending on drainage work. Such soils are not only easily compressed and eroded, but also rise, swell at sub-zero temperatures, pushing out the foundation.
The most important parameters that you need to know when developing a site:
It is they who determine how the project corresponds to the area, and dictate what foundation it is advisable to lay here. The first parameter has its own "regional standards". However, there are always local peculiarities, so it is extremely useful to get information from the nearest, professionally developed areas.
GWL does not lend itself to even approximate standardization. You can only believe the results of competently carried out engineering and geological work in a given place. But with the results of preliminary research on hand, it is not a sin for the customer himself - and it is not difficult - to make general calculations. And if it turns out that the groundwater level is higher than the freezing depth, do not skimp on taking appropriate measures to protect the foundation. The cost of the most expensive "prevention" is incomparably lower than the losses for "treatment".
Engineering and geological research. These include studies of the composition and properties of soil taken from pits drilled at the site, and chemical analysis of water. When building wooden houses, the depth of such wells should be 5 m, for brick and stone - 7-10 m. At the same time, at least four wells are required, at least in the corners of the future house, and preferably every 3 meters.
It makes sense to point out a few more important aspects related to the depth of the foundation. So, the standard depth can be reduced under certain thermal conditions of the building, since in heated rooms the heating of the soil largely depends on the construction of the floor and its materials.
The depth of the foundation also depends on the specifics of the relief, and for a building without basements - on the planned underground communications, the nature and magnitude of the loads.
[box] Belt, columnar, pile… Is there a choice? [/ box]
In the finished project, the type and construction of the foundation correspond to the main material of the house - wood, brick, reinforced concrete blocks, frame, etc. - and its number of storeys. However, the soil conditions and the topography of the site can make "forced" adjustments in the direction of strengthening - hence the rise in price - of the support of the house, or, conversely, allow a pleasant economy. It is worth setting aside time to discuss the issue with professionals. And, above all, one should not succumb to the well-known prejudice that it is better to build the foundation as deep and massive as possible.
The foundation is "combined" of the selected type of structure (tape, solid, columnar, pile) and the technology of laying (prefabricated, monolithic). Accordingly, if the laying is made to a depth of 5 m, then the foundation will be considered shallow, and if deeper than this mark, then deepened. Here we note that when the excavator is operating, it is better to make a trench under the foundation at first about 20 cm above the approved depth for subsequent careful finishing (stripping, leveling) manually.
This approach significantly improves the quality of the foundation sole. These preparatory steps (axle set-out, excavation and soil compaction) usually account for 5 to 25% of the total foundation cost.
The type of foundation is determined primarily by the severity of the house, the presence or absence of a basement and basement, and the properties of the soil. A two or more storey cottage with heavy structures on sufficiently strong and dry ground is usually placed on a strip foundation, prefabricated or monolithic.
On heaving soil with active dynamics of groundwater, a slab foundation is optimal. The latter, in fact, is combined, since the same strip foundation is laid on top of reinforced concrete slabs (solid, precast-monolithic or monolithic-cross), as on a raft. This design is optimal on any soil for buildings made of lightweight frame structures.
Make sure that, in order to avoid possible subsidence and decay, the vegetative layer of soil has been removed before starting to dig trenches or pits throughout the entire area of the building, including the blind area.
Formwork for the foundation... Advanced professionals put in the pit a reusable metal, and not "outdated" wooden formwork, into which reinforcement is placed and concrete is poured. Such formwork provides the foundation with a smoother and more even, and therefore a more durable and cold-resistant surface. A true professional, in addition, makes a concrete ingot with the date of pouring and gives it to the customer, complete with a concrete passport, a certificate and a receipt from the receipt.
There is a known problem of choosing between strip prefabricated and strip monolithic foundations. The supporters of the former rely on many years of experience in construction projects, on the reliability, durability and cost-effectiveness of structures made of reinforced concrete blocks, on the fact that such foundations have shown their effectiveness in the northern regions, in places with high GWL and highly heaving soils.
However, a prefabricated foundation, although it is cheaper for a monolithic one (by about 20%), requires more skill and professionalism (specific arrangement of blocks, adjusting them in corners, filling seams and gaps, arranging more reliable waterproofing), as well as special equipment and platforms for it. installation.
Monolith, almost universally used in the West, requires less engineering and technological costs and the hassle of waterproofing. Practice also shows that the monolith is optimal in the presence of heavy load-bearing walls in the project and, moreover, only it is suitable in conditions of excessive heaving of soils. Important points that are not a sin to track to the customer himself: the compaction of a cushion of sand and gravel at the bottom of the excavation (for sandy and sandy loam soils, a gravel cushion is sufficient) should be carried out using a vibrating electric plate, and not manually, and - each layer should be separately waterproofed before laying the reinforcement protected by acent or slate pauses in the process, especially before pouring concrete, should not be in order to avoid loosening and crumbling of the soil under the influence of rain and drops in air humidity. There is a known problem of choosing between strip prefabricated and strip monolithic foundations. The supporters of the former rely on many years of experience in construction projects, on the reliability, durability and efficiency of structures made of reinforced concrete blocks, on the fact that such foundations have shown their effectiveness in the northern regions, in places with high ground water levels and highly heaving soils.
However, a prefabricated foundation, although it is cheaper for a monolithic one (by about 20%), requires more skill and professionalism (specific arrangement of blocks, adjusting them in corners, filling seams and gaps, arranging more reliable waterproofing), as well as special equipment and platforms for it. installation.
Monolith, almost universally used in the West, requires less engineering and technological costs and the hassle of waterproofing. Practice also shows that the monolith is optimal in the presence of heavy load-bearing walls in the project and, moreover, only it is suitable in conditions of excessive heaving of soils. Important points that are not a sin to track to the customer himself: the compaction of a cushion of sand and gravel at the bottom of the excavation (for sandy and sandy loam soils, a gravel cushion is sufficient) should be carried out using a vibrating electric plate, and not manually, and - each layer should be separately waterproofed before laying the reinforcement protected by acent or slate pauses in the process, especially before pouring concrete, should not be in order to avoid loosening and crumbling of the soil under the influence of rain and changes in air humidity.
In any case, on heaving ground, the strip foundation should be a solid frame, which is created by a rigid system of intersecting belts. For laying shallow foundations, in addition to concrete, other, quite economical materials are used that are acceptable for small one-story houses. On dry, non-porous soils, sand with additional layers of gravel, crushed stone and broken brick is often used, as well as brick. The latter requires additional measures to protect against moisture. Rubble foundations, record strong and durable, are laid from large cobblestones and stone debris caught in cement mortar. Rubble concrete foundations, built in a formwork or a trench with vertical walls, consist of a mortar filled with fine crushed stone and gravel.
Columnar foundations (the range of materials for them is very wide) are optimal for the construction of wooden and frame houses without basements and basements on heaving soils with a large freezing depth, as well as in cases where the underlying soil lies at a depth of 3-5 m. these foundations are platforms with a height difference, where it is contraindicated to lay them.
Foundations of this type are very economical: in terms of material consumption and wages, they are almost twice, and when deeply buried, they are sometimes five times cheaper than tape ones. But there is one significant problem: the need for a so-called pick-up, a connecting wall between posts made of brick, concrete or rubble masonry to insulate and protect the underground space. Finding masters who know how to do it correctly is, alas, sometimes not an easy task.
A kind of columnar - pile foundations. They are becoming more widespread in projects of one-two-story houses, since they are very effective in weak soils and high groundwater levels. The piles are either used ready-made, or they are made directly in the drilled wells. Stand piles are used, with the bases reaching solid soil, or hanging piles, which create support due to soil compaction and friction force. Pile foundations are considered the most environmentally friendly in terms of the degree of impact on the soil landscape of the area. Moreover, they are increasingly viewed as the most progressive. However, the same problem still remains - the lack of professional staff. Therefore, when including a pile foundation in a project, it is important to enlist the support of specialists.
[box] Filisols, acrylics, styrenes ... How to insulate? [/ box]
Waterproofing is akin to the human immune system. And it is important not only for the "health" of the building itself, but also, to a large extent, for its owners. In the structure of costs for the foundation, it takes 5-10%.
With a serious approach, waterproofing is "lined up" in three lines of defense at home.
The main types of waterproofing used in construction with soil separation along the perimeter of the building are coating, painting, cast, pasting, surfacing, injection, penetrating. Which ones should be used in a particular case, can only be advised by a specialist.
The most advanced types are penetrating and injection types of insulation. Among the first, mastics based on chlorosulfonated polyethylene and polyurea, applied to the surface of the foundation under pressure, show very high efficiency. These materials developed in Russia are extremely resistant to the aggressive effects of natural factors, do not decompose and, as a result, are extremely durable. Other advantages: the quality of such insulation is easy to control, it can be applied to fresh concrete, and also worked with it in winter at temperatures down to -15C.
Another very promising Russian development deserves special attention - natlen, a bulk material based on activated bentonite clay. When in contact with water, it forms a kind of gel barrier that traps it. It is shown that at a pressure of 40 atmospheres, water penetrates into the natlen layer by no more than 2-3 cm. Thus, a 4-cm natlen layer (with or without formwork) is quite enough for reliable protection of the foundation.
Penetrating insulation technologies are actively developing. Special compounds are applied to the wet surface of the foundation and, due to moisture, are absorbed into microcracks and pores, clogging them, and then, drying out, pass into a solid crystalline phase. With the formation of new cracks and natural access to them of soil moisture, the process resumes, spreading to new areas: the insulating material "lives", making the surface of the foundation healthy.
In a sense, this technology is akin to the technique of injecting soil adjacent to the foundation (and basement walls, if any). In this case, from the surface of the earth or directly from the basement through the body of the foundation, wells are drilled to a standard depth and reinforcing waterproofing materials are injected into them under high pressure. Thus, a kind of protective "sarcophagus" is created around the underground part of the building. The composition of the injected solutions is determined depending on the engineering-geological and filtration parameters of the soil, as well as the type and condition of the foundation. The most commonly used against flooding today are materials based on epoxy, polyurethane and acrylic resins. Technologies have also been developed to protect against rising capillary moisture by injection under low pressure.
Roll materials, such as hydroglass, filisol and others, remain in widespread use. They have their advantages, the technologies for their laying have long been worked out, however, with the available choice of materials, their disadvantages begin to come to the fore. They decompose relatively quickly. The control of the seams is rather difficult. The “human factor” means too much when laying them - technology violations are often allowed.
Remember the importance of the initial planning of the entire site with the obligatory slope device to drain surface water from the house. And also - about the enduring waterproofing role of the blind area, which ends the zero construction cycle.
The "theme" of groundwater should be supplemented with one more problem that may arise already in the process of pouring the foundation. When the soil is saturated with water, in order to avoid silting of the pillow, it is necessary to treat it along the contour with binders or by covering it with a polymer film.
Blind area... It should be up to 1.5 m wide and done in three layers: first - soft, well-compacted clay, then - broken brick or crushed stone, and outside - cement mortar or asphalt. It is better to put the last layer one year after laying the first two. By the way, the blind area is the only "design" part of the zero cycle.
[box] Thermal insulation [/ box]
This area of security technology lives on with its own traditions and priorities. This area of security technology lives on with its own traditions and priorities. Technologies in it are rapidly developing, bringing new brands to the market. However, in most cases, the basis, arranged directly on the plane of contact between the soil and the structures of the house, remains the claydite used for a long time, placed on the sand. The expanded clay layer must be protected by the so-called cement milk. A concrete screed is placed on top. On it, if there are no basements and basements, there are reinforced concrete floors. In the presence of a basement, expanded clay is used much less often. In this case, the most common technology is pasting the inner walls of the basement on the bitumen mastic with foam (20 mm), which is then plastered over a chain-link mesh.
Among the progressive materials, the main ones are basalt wool (ROCKWOOL, ISOROC, PAROC, etc.), staple fiberglass (URSA, ISOVER), extruded polystyrene foam (in particular URSA XPS, PENOPLEX). Basalt wool is durable, does not shrink, does not burn (it is also used as fire insulation!), And is environmentally friendly. We recommend using this insulation impregnated with water-repellent compounds, as well as protecting it from the inside with a vapor barrier material.
Staple fiberglass is also very effective, it is resistant to chemical attack and has antimicrobial properties. It is also recognized as the best sound insulator. At the same time, like basalt wool, it should be protected from steam and water (special solution plus foil).
Extruded polystyrene foam is durable, withstands sudden temperature changes, moisture resistant, and therefore is especially suitable for warming foundations and basements. It is usually glued to a layer of waterproofing to avoid areas that carry cold into the room - "cold bridges". At the same time, it protects the waterproofing from freezing and mechanical damage. It is only important to protect it from direct "hit" of sunlight before use, otherwise the material may crumble.
According to various estimates, the cost of thermal insulation for different types of foundations ranges from 5 to 15% of all costs for its construction.
[box type = ”info”] In conclusion, we draw your attention to a number of fundamental construction details subject to the customer's control [/ box]
Work is best done in summer, when weather conditions are favorable. It is unacceptable to pour a shallow foundation on a frozen base. Do not succumb to the old delusion that the foundation needs to be defended before the walls are erected. It is necessary to put the box of the cottage before the ground freezes and begins to actively push out the unloaded foundation. It is important at the beginning of construction to look into the pit with a specialist and make sure that all the embedded elements - for the sewage system, cold water inlet, grounding - are not forgotten, introduced and introduced correctly. Finally, when choosing a contractor, you should rely on a company that already has experience in construction in the area.
Having made an analysis of the soil, the climate of the area and taking into account the number of storeys of the house, the thickness and height of the strip base are calculated. If a support for a house is created according to a finished drawing, then everything is done independently. In order to avoid mistakes, the work is performed according to step-by-step instructions.
For the construction of a one-story brick house on fine sandy soil (Moscow region), with an area of 60 m, with dimensions of 5x12x5.5 m, a drawing is created and the following calculations are performed. They look at other data, such as the level of occurrence of groundwater (1.4 m) and the interval from the planning mark to ground currents during the period of their freezing (2 m). Taking these data into account, a foundation with a width of 0.4 m is laid at a depth of 1 m.
The length of the base for the house, which is redistributed into 2 rooms (20 m and 40 m), will be 39 mx 0.4 m = 15.6 m. After that, the structural elements and materials for them are determined. Calculate the flow rate as follows. For example, concrete grade M150 for a monolithic foundation must be ordered 0.4 mx height 1.0 mx length 39 m = 15.6 mx 2500 kg / m (specific gravity of reinforced concrete) = 39 t.
The strength of the house itself will depend on how accurately the foundation is calculated
How many solid ceramic bricks are required for a basement:
After determining the weight of the whole house, loads, specific pressure on the soil, the foundation is checked and adjusted. Sometimes the size of the base is changed to reduce costs. After that, everyone clarifies and receives the final figures, which are taken into account when building.
The first stage in building a house is considered to be marking and earthwork. The sole always rests on solid layers of soil (clay, sandy loam, stony layers, loam), which are located under the sod or earth. Everything needs to be cleaned up and the construction site cleaned up.
Before marking the foundation, the area must be cleared of debris and grass
Construction technology sometimes involves some amount of work, so additional equipment is involved: an excavator, a dump truck, etc. And it all depends on whether or not there is a basement in the layout, since in this case a pit is dug, and in another - trenches.
When digging, remember about safety precautions. The width of the ditch is made slightly larger, since formwork is subsequently installed in it. The walls should have a slope so that the soil does not crumble, props are made.
Trench for strip foundation
To arrange the basement, a pit is dug, and a crushed stone pillow is installed along its bottom and poured with concrete. For strength, reinforcement is performed. In the places where the walls are installed, rods should stick out.
If there is no basement in the project, then the bottom of the pit is leveled with sand and fine gravel. Ramp down. The height of such a layer should be from 10 to 30 cm. This pillow is necessary to reduce the point load and its redistribution to the foundation during the seasonal swelling of the soil.
For a reinforced concrete base, there are two types of formwork: removable (boards, bars or laminated chipboard) and non-removable. When using the first type, roofing material or plastic wrap is placed in it, which do not allow the cement to pour out. And the second type is made of expanded polystyrene and is designed for additional heat and waterproofing.
So that the mortar does not leak out for the construction of the formwork, you can use moisture-resistant plywood
A frame is formed in the trench (cells must have a side from 25 to 30 cm) from steel rods with a section of 14 to 16 mm. They must be laid taking into account that the steel is subsequently covered with concrete. The distance from the insulation to the reinforcement is 5 cm. When tying the reinforcement, electric welding is sometimes used.
Reinforcement rods are installed in a trench and tied together with knitting wire
In order for the concreting to proceed normally and voids do not form in the base, the still uncured concrete is pierced with a bar and air is released, or a construction vibrator is used for this purpose. A few days later, waterproofing work is carried out and blind areas are installed.
Concrete mix - easy and quick to prepare, especially if you use a concrete mixer
Useful tips for pouring a strip foundation
When building a house, builders often prefer a strip foundation due to its reliability and ease of construction. The main thing is to comply with all building codes, since any violation can further lead to the fact that the house can squint or settle, and this entails the curvature of the roof and windows. It is advisable to take seriously the construction of a strip foundation with your own hands from the very beginning.
This post will tell you about how to build a shallow or shallow foundation, that for this you need to know what conditions and requirements to fulfill for their construction.
In order to write this material, a lot of information was collected from various sources, their analysis was carried out, the main part was taken from the development of the central research, experimental and design institute, the Ministry of Rural Construction of the USSR. This work was carried out by them in 1985; in our time, no one is doing this.
Everyone has probably read it and you know that the foundation is laid at the calculated freezing depth, since there water does not freeze under its sole and thus does not push it out, in simple words. But at the same time, what we have, and we get the following problem, increasing the area of the outer part of the foundation, which contacts the heaving soil tangentially, since there is friction between them.
If, for example, you are planning a light house, made of modern materials, such as aerated concrete, in my case, or others, then these forces can easily lift it - bulge it out.
That is, in our case, larger, deeper and thicker foundations, laid below the freezing depth, do not give any guarantee that cubic meters of laid concrete and the tones of buried reinforcement will save you from these insidious forces.
Based on the above, smart people have found application through calculations and experiments. shallow foundations on heaving soils, which can be laid to a depth of 20 to 50 centimeters, or not at all, and thus get unburied foundation.
If we take into account the above, then we get that the tangential heaving forces that act on a shallow foundation are very small, and for a non-buried foundation, they are absent as such.
The designs of shallow foundations are aimed at reducing the force of heaving of soils, or reducing them to zero. For those who want to build their house quickly, reliably and cheaply, just this type of foundation is suitable, but much depends on certain conditions, which are described on this page.
This is achieved through a number of measures aimed at removing surface water from the side walls and the bottom of our foundation. Why make a drainage system, with a high position of groundwater, replace the heaving layer of soil with a non-heaving layer (sand, crushed stone, gravel), carry out actions to increase the temperature around the foundation (side walls and blind area) by using heat-insulating materials.
As for the cushion for shallow or shallow foundations, it is 20-30 cm, as mentioned above from non-porous materials, it can be gravelly sand, coarse or medium fraction, boiler slag or the well-known fine crushed stone.
To ensure normal operation shallow or shallow foundation, it must be quite tough, that is, the material is reinforced concrete, especially this condition should be applied for soils with strong heaving. Why this is done, everything is very simple, in order to distribute the uneven load from heaving, since in different places of the building it will be different, for example, in its northern part it is more, and in the south it is less.
In the former USSR, more than 1,500 houses were built, mainly those regions where the freezing depth is up to 170 cm, with various materials, in one and two floors. These buildings were monitored by employees of the institute, for 3-6 years and shallow foundations perfectly cope with the loads placed on their shoulders. As for the economic point of view, it is obvious and consists in the following figures: labor costs are less by 40-70%, and the amount of required concrete has also dropped by 50-80%.
but - not buried on the leveling bed,
b - not recessed on a pillow made of non-porous material,
in - not buried on a bed of non-porous material,
r - shallow on a leveling bed,
d - shallow on a pillow made of non-porous material,
1 - foundation block,
2 - leveling, sand bedding,
3 - a pillow made of non-porous material,
4 - backfill made of non-porous material,
5 - bedding made of non-porous material,
6 - blind area,
7 - waterproofing,
8 - building wall.
I also wanted to add, if you need to increase the bearing capacity of the base, for this it is advisable to make a pillow of sand and crushed stone in a ratio of 2/3.
Below we will consider when and which of the above foundations is used under certain conditions, their design features, depending on the heaving force.
When building walls from bricks, blocks and panels on a strip shallow foundation, you must adhere to the following conditions:
— if the ground is not heaving - the foundation should be made of concrete or expanded clay concrete blocks without bandaging, loosely laid
— on strongly and medium heaving - if concrete and similar blocks are used, they must be rigidly connected to each other, and best of all, monolithic reinforced concrete
- as an option: armopoyas - precast concrete blocks - armopoyas
— if the soil is very heaving- then you will be saved only by a monolithic reinforced concrete base and plus to it, you need to make an armored belt after the construction of the first floor, on which the floor slabs will subsequently be laid.
When building walls made of wood or on frame technologies(Canadian houses) on a strip shallow or shallow foundation, you must adhere to the following conditions:
— if the ground is not heaving- the foundation should be made of prefabricated concrete or expanded clay concrete blocks without bandaging, loosely laid
— on medium heaving - you can use reinforced blocks with a standard size of 250 mm by 200 mm, but no longer than 2000 mm, they must be laid in two rows in order to tie the seams
— if the soil is very heaving- in this case, you need to use reinforced concrete or blocks rigidly connected to each other.
As a variant of such a technical solution, you can see in the picture.
If the house is being built on very and medium-heaving soil and will stand on a columnar shallow foundation, then its structure should be a single rigid system, it is called a grillage.
The beams that connect the pillars of a given base can be left unconnected only if it stands on non-heaving or slightly heaving soil.
You should also take into account and do not forget about the gap between the beams and the surface of the earth, so that they do not rise when heaving.
I think that rarely does anyone build houses more than 15 meters long, mostly industrial buildings, well, if you suddenly have to, then you should take into account the following dependence and build them as separate boxes on their foundations, that is, divide them into sections.
Estimated bulk density of building materials, kg / m3
Granite crushed stone - 1500
Limestone crushed stone - 1300
Gravel - 1600
Quartz sand with a moisture content of 5% - 1500
Expanded perlite sand - 300
The maximum length of buildings, depending on the degree of heaving of the soil:
- no more than 15 m - super chubby
- up to 20 m - very heaving
- no more than 25 m - medium heaving
- up to 30 m - slightly heaving.
Well, in principle, and all that I wanted to tell you today about shallow and shallow foundations, you learned which structures are used depending on the types of soil.
Red brick has been used for construction for a long time, nevertheless, despite the fact that many other building materials have been released, it is successfully used for the construction of load-bearing walls of houses, as well as for the foundation, although this is done less often now than before. If you opted for this material and decided to make a brick foundation with your own hands, then it is important to know in what conditions it can be used, and what types of foundation are made with it.
A question from a reader of our portal: How is a columnar foundation built from blocks and pipes with a grillage?
Answer: Before proceeding with the construction of a columnar foundation, you need to correctly determine the type of soil. It is advisable to conduct a soil analysis and consult a specialist, as well as talk with the owners of neighboring plots, especially if there are people among them who are versed in construction. They can share their own experience of building a foundation, such as providing valuable advice on foundation depth. This can significantly save time, effort and money, because an incorrectly determined foundation depth can become a problem in the future.
If you plan to build a wooden bathhouse on heaving ground, then it is best to build it on a columnar foundation. What is a columnar foundation?
Column foundation - these are free-standing pillars that serve as supports for the walls. Its design is optimal for light structures - timber or frame - but not suitable for heavier ones. The main disadvantage of a columnar foundation is that it is impossible to make a cellar or basement in buildings erected on such a basis. However, reliability and economic efficiency (including the absence of costs for additional waterproofing) fully compensate for this disadvantage.
Materials for the construction of a columnar foundation - brick, rubble concrete, reinforced concrete and rubble stone. In this case, it is better not to use silicate or red slotted bricks. A small light bath can even be installed on wooden poles, but such a support will be very short-lived.
The calculation for a columnar foundation is quite simple. First, the pillars are installed in the corners of the future bath, then in all places with increased load (for example, at the intersection of walls). The pillars are placed at a distance of 1.5 to 2.5 m, and the step size depends on the load on the foundation: the higher the load, the smaller the step.
The optimal size of brick or stone pillars of the foundation is 51 × 51 cm.For the construction of a light bath, smaller pillars can also be used - for bearing pillars, the cross section can be 38 × 38 cm, and for intermediate pillars - 38 × 25 cm. If the bearing pillars are made of rubble stone, then they should be slightly larger - 60 × 60 cm.Also, for the construction of a columnar foundation, pipes made of asbestos cement can be used, and the diameter of such pipes should be 20 cm.
For a columnar foundation, it is necessary to dig holes below the freezing of the soil. If you plan to lay a columnar monolithic foundation to a great depth, then you need to equip a sand and gravel cushion. To do this, cover the material with a layer 20 cm thick and compact it well.
The space between the bearing supports must be covered with coarse sand or crushed stone, then a layer of concrete or reinforced concrete should be laid. In order to protect the entire structure from dust and moisture, you need to make a "pick-up" - a wall that connects the posts to each other. It will make the structure more stable, prevent water from entering and help keep warm.
If the foundation is being built on heaving soil, then first you need to equip a sand cushion with a layer 15 - 20 cm thick. 20-50 cm. The upper part of it must be leveled with cement mortar, and then a two-layer waterproofing made of roofing felt or roofing felt.
After the construction of the columnar foundation, you can start building the basement. The plinth is necessary in order to protect the floor from dampness, dust and cold. There must be at least two vents on opposite sides of the plinth.
As a rule, bricks, blocks, flat sheets of asbestos and wood are used in the construction of a basement. The most economical and completely reliable option would be a basement made of flat asbestos slate. To erect the basement, the slate sheets must be cut with a jigsaw into three parts equal in length.
A concrete lintel must be installed between all posts. To do this, you need to dig a trench about 30 cm deep, fill it with a 15-cm layer of sand and tamp it. Then the trench must be filled with concrete and the slate sheets must be installed, making sure that they fit evenly and tightly to the foundation pillars. The slate must be buried in concrete so that its edge is the same height as the supporting pillars. It is also important not to forget that it is necessary to cut holes for vents. Self-tapping screws are used to fasten the slate sheets, and from above, a strapping with a corner of 25 mm is required.
The same corner is used to close the joints of the slate sheets. Between them, you need to lay polyethylene, then insert asbestos-cement pipes into the vents, fill the space between the slate sheets with expanded clay and concrete the pipes. This completes the construction of the basement.
Of course, a theoretical description of the processes of building a foundation cannot replace real construction experience. But, since experience comes only with practice, then someday you will definitely have to move from theory to practice.
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The foundation is made of durable materials, although sometimes even wood or sand... Here are brief characteristics of each type of foundation.
Can only be laid on dry soils. On wet soils, laying is allowed burnt clay brick... It is not recommended to build this type of foundation with an elevated water table. Suitable for the construction of capital and multi-storey structures from almost all materials
The basis of the rubble foundation is large cobblestone or limestone... The foundation is strengthened using cement mortar. Rubble foundations remain stable on heaving soils and are suitable for deep laying. Withstand buildings of almost any number of storeys and sizes
For its construction are used concrete blocks or mixtures that are stacked in layers. The walls can be located at different heights, they can be given any configuration. Buildings of any complexity, number of storeys and layouts can be erected on a concrete base
The strongest and most durable type of foundation. Does not "float" even on heaving ground. There are monolithic and prefabricated types. Buildings on its basis are erected "for centuries"
Ideal for the construction of temporary buildings, one-story houses and buildings with low traffic. It is good to lay it on non-loose soils and flat surfaces.
It is rarely used in the middle lane. Mainly for the construction of small buildings: baths, gazebos, sheds, summer kitchens, greenhouses. Withstands minor deformations and is also easy to install. Disadvantages - short service life and low strength