Shallow foundation on heaving soil

Building a house on a private plot with heaving soil is, first of all, closely related to proper design. And it is the foundation on heaving soils that deserves special attention here, since the reliability and durability of the entire house depends on the foundation and its strength.

It is known that seasonal heaving of the soil has a negative impact on the foundation of the house, namely, it pushes it out, which leads to the destruction of first the walls of the frame, and then the walls of the house itself. Therefore, it is worthwhile to approach the issue of foundation design very carefully.

Important: if you have even the slightest doubt about the correctness of the previously made decision, you should invite a specialist who will analyze the soil, determine the degree of heaving and design the optimal basis for the house.

Climatic conditions.

Russia is a huge country, and it has a lot of regions with different climatic conditions. A building on a shallow concrete foundation in the Krasnodar Territory will behave somewhat differently than a similar structure in the Altai Territory. This is primarily due to the fact that in these regions climatic conditions affect the soil differently.

Severe Siberian winters cause water in the ground to freeze to great depths. As you know, when water freezes, it increases in size and, accordingly, the water in the soil will also expand when it freezes. Along with microscopic drops of water, the entire volume of the soil will expand, which will inevitably lead to “heaving” of the soil. Different types of soil have different coefficients of expansion due to defrosting.

To avoid the influence of soil expansion during temperature changes on the foundation, it can be thoroughly buried in the ground, below the soil freezing level. This approach is good for permanent residential buildings, since a deep strip concrete foundation, in addition to imparting stability to the structure, also allows you to create functional rooms in the basements and basement levels of your building, which significantly expands the usable volume of the house.

Design of shallow foundations on heaving soils

Shallow foundation design.

But such a deep foundation will cost you a pretty penny. Therefore, for domestic and outbuildings, even on heaving soils, shallow strip foundations are used. However, when building on this kind of frozen areas, you should use some construction tricks.

Fighting heaving using engineering and reclamation methods

Raising the level of the construction site due to the method of filling medium or coarse sand from non-heaving soils. This method will help reduce the depth of possible freezing of soil prone to swelling.
Deep drainage. This method is ineffective if there is no basement. It cannot be called extremely affordable, but this is the method that will allow you to avoid flooding or deformation interventions if you have a basement or cellar that needs insulation.
Compaction with heavy tamping, which reduces soil porosity. For individual construction, this method is quite labor-intensive and quite expensive, since it requires the use of powerful mechanisms and equipment.

Construction of a shallow strip foundation on heaving soils.

As with any construction, the initial stage is the creation of a project. In our case, we need to avoid the force of pressure of the soil expanding during freezing on the walls and base of the strip concrete foundation. To do this, we place the foundation tape almost on the surface, only removing the top fertile layer.

Thus, there will be practically no pressure on the walls of our foundation. But we will compensate for the pressure that will come from the expanding soil below with the weight of the building itself. In addition, in a shallow strip foundation on heaving soil, it is necessary to provide blind areas that will insulate the adjacent soil and prevent it from significantly changing in size.

Thermally insulated shallow foundation (TFMZ)

It should be taken into account that the degree of frost heaving of the soil and the strength of building elements may change over time.

This creates an ongoing risk for buildings built on the foundations described above.

A modern way to solve the problem of frost heaving for a private house is to use a thermally insulated shallow foundation (TFMZ)

Any foundation structure can be thermally insulated. To do this, the foundation itself, as well as the soil under and around the foundation, is insulated with a layer of thermal insulation.

Fig.1. Layout of thermal insulation in the foundations of heated buildings.

1 - foundation; 2 - wall; 3 - floor; 4.5 - horizontal and insulation ; 6—protective coating ; 7 - sand preparation; 8 - blind area; 9 - PGS ; 10 - drainage; 11 - floor insulation.

Thermal insulation of the foundation prevents freezing of the soil near the foundation, which makes it possible to ignore the impact of frost heaving forces on the building.

The use of modern heat-insulating materials to insulate the foundation makes this method more cost-effective, allowing to simplify and reduce the cost of building construction, avoid risks,

associated with errors in design and construction, with changes in soil properties and strength of the building during operation.

Read: “ How to make a thermally insulated shallow foundation - the best for a private house”

Construction order.

Calculation and design of the foundation.

So, first we create a foundation project. Typically, a shallow strip foundation is located under the outer perimeter and internal load-bearing walls of our building.

Scheme of a shallow foundation on heaving soils.

Foundation laying diagram.

In our case, it will not be buried deep into the ground, but will be poured almost directly on the surface. The main characteristic that we will need to lay in this foundation is strength, that is, the ability to withstand pressure of a certain number of units of weight on a surface area. This characteristic of concrete usually coincides with its brand. That is, M200 grade concrete is capable of withstanding a pressure of 200 kgcm2 without destruction.

Main mistakes when laying a foundation:

In order to understand what concrete strength we need, we calculate the expected weight of the building structure, including walls, floors, payload, etc., and divide the weight by the area of support.

We mark a shallow strip foundation.

We mark the boundaries of the future foundation on the ground. We use a marking cord to mark the boundaries of the foundation support. To create a perfect rectangle, stretch the cords along the diagonals of the resulting markings. The diagonals of the rectangle must be the same.

Marking a shallow foundation on heaving soils.

We prepare the site.

A shallow foundation trench on heaving soils.
We prepare the site for the construction of the foundation

At a prepared and cleaned construction site, we remove the top part of the soil along the marking cord. Instead, we lay a sand cushion about twenty centimeters thick. Among other things, it will also compensate for temperature deformations of the soil.

We are building formwork for a strip foundation.

From the ground level we begin to build wooden formwork for the strip foundation.

To ensure that the wooden formwork of the foundation strip does not fall apart under the influence of the weight of the concrete solution, we firmly fix the opposite sides of the wooden formwork body together. To do this, we knock down wooden panels or chipboard panels together with connecting bars or tie them together with wire. We fix stops located diagonally on the outer sides of the formwork.

We install the reinforcing frame.

In order for our strip foundation to resist loads equally well in all directions, there must be a spatial metal frame inside it, made of reinforcing rods.

Do-it-yourself shallow foundation on heaving soil.

Installation of the reinforcing frame.

This frame looks like a metal cage that does not touch the edges of the future casting. Metal rods can be connected to each other by welding (but only if they are marked with the letter “C”), as well as by pieces of binding wire or ordinary construction clamps made of plastic.

Preparation of concrete mortar.

There are two ways to fill the prepared formwork and metal frame with concrete mortar.

Firstly, you can simply order a machine with industrially produced concrete with specified characteristics.

Secondly, you can mix the concrete solution yourself. This will be advisable if you do not have a very large amount of work to do. In order to mix concrete with the given characteristics, we need to know its proportions, which can be taken from the table below.

Types of concrete mortar for shallow strip foundations on heaving soils.

Types of concrete mortar.

If you mix concrete in several stages, then place it in the formwork in layers. When laying concrete, it is necessary to ensure that it evenly fills the entire volume of the formwork and that no voids form in it. To do this, it is compacted and the concrete solution is also exposed to vibration drills.

Maturing of concrete.

The concrete solution matures to high-quality concrete within a few weeks. During this process, especially in hot weather, it must be protected from excessive drying by spilling water on its surface.

Insulation of concrete shallow strip foundation.

There is another construction trick that will allow you to build a shallow foundation on heaving soils. This is insulation of the earth around the foundation. The idea is that under an insulated foundation, the depth of soil freezing becomes much less, and, therefore, its expansion during freezing also becomes less.

A diagram of this phenomenon is shown in the figure.

Shallow slab foundation on heaving soils.

Freezing soil sample.

Thus, areas are created under the foundation where the soil does not freeze at all or freezes to a shallower depth.

The next idea is to expand the insulation zone. There is no need to expand such space inside the house. If the house is heated in winter, then the temperature underneath will be maintained, preventing the soil from freezing and, consequently, from “heaving”. However, such a frost-free zone should be extended from the outer perimeter of the house. It would be optimal to expand the soil insulation zone by about a meter from the perimeter of the foundation.

The fact is that the soil freezes from top to bottom, under the influence of cold atmospheric air. If you isolate the soil from frosty air, the water in it simply will not freeze.

Therefore, there is an additional perimeter of thermal insulation or blind areas around the foundation of the house.

Video - technology for constructing a shallow foundation on heaving soils.

Measures to counteract tangential heaving forces

It is possible to counteract the tangential forces of heaving when constructing a strip foundation by carrying out a number of measures:

construction of not a prefabricated, but a monolithic reinforced concrete foundation
filling the bottom and sinuses of the trench under the foundation with sand: the wider the layer of lateral sinuses, the less the influence of tangential heaving forces
a significant increase in the depth of the foundation in order to increase the total mass of the structure to a value that will exceed heaving forces
anchorage of foundations: expansion of the lower part, which will be affected by reactive, downward heaving forces
adding coarse sand to raise the general level of the site: thereby reducing the depth of soil freezing under the building
installation of drainage trenches, which is especially important when the groundwater level is high
foundation insulation measures

Materials for you:

Pile bearing capacity
How much does a house foundation cost?

Which foundation is suitable for heaving soils?

Foundation installation on heaving soil
Foundation options for heaving soil Strip shallow foundation
Uneven shrinkage of structures on heaving soils

Calculation for a shallow foundation

Heaving soil is not the best option for construction, since it is associated with the need to solve a number of problems, in particular, neutralizing winter heaving of the soil. that is, movements that can be dangerous for the foundation and the structure as a whole. That is why experts recommend making a shallow foundation. which copes well with loads without being subject to uneven shrinkage and destruction. One of the popular ones is a shallow strip foundation. which is relatively easy to implement, such a base is suitable for almost any structure.

Shallow foundation on heaving soil.

For a strip shallow foundation, it is necessary to dig a pit 50-70 cm deep and lay waterproofing in the form of roofing felt on the side slopes.

Different types of soil heave

Let's consider the main types of ground heaving.

Vertical

The movement comes from bottom to top, causing the base to be “pushed out”. If the base of the foundation is located in a layer of frozen soil, then the foundation will be subject to vertical heaving. If it is located below the freezing mark, there is no threat of heaving.

Tangent

The action of the forces of frost heaving of the soil
Due to the occurrence of friction of the expanding soil against the walls of the foundation, the foundation is pushed out. However, the magnitude of tangential frost heave is significantly less than vertical frost heave.

The problem arises when it comes to lightweight wooden or frame houses. The weight of lightweight structures cannot compensate for the buoyancy forces.

Winter heaving of the soil and a decrease in volume in the spring cause subsidence of the soil, the foundation above it and the entire structure. Consequently, damage and cracks are possible.

Construction of the foundation on heaving soil.

The construction of a foundation on heaving soils is undesirable because the heaving force can be large and can easily lift entire buildings. That is why it is so important to choose the right type of foundation, and during its construction to follow a number of measures to reduce this negative phenomenon.

One option is to replace heaving soil up to the freezing point with sand. This method is the most reliable, but its cost is high and it is not always advisable. Another option is to use foundations that lie at a depth below the freezing point. These are columnar and pile structures. Heaving forces do not apply to them, but the construction of such foundations can be very costly, that is, not entirely profitable.

The third option is a shallow foundation, which, along with high strength, also ensures the stability of the house. It successfully resists heaving and does not give strong and dangerous shrinkages. Most often this is a shallow shallow foundation made of monolithic reinforced concrete.

Foundation for a frame panel house.

Scheme of types of strip foundation.

Such a shallow foundation is placed on a sandy base, which is covered with a layer of waterproofing; the walls of the trench are reliably protected using special materials. It is recommended to add water-repellent additives to the concrete solution when mixing, which increase the stability of the material. After constructing the foundation, you need to worry about creating a drainage system that effectively removes excess moisture from the structure. To build the base, in addition to the concrete itself, reinforcement should be made of a strip of metal rods with a diameter of 12 mm, and their number will be slightly larger than for a conventional strip base.

Anti-heaving measures

Key stages of construction of the MZLF are carried out taking into account the need to protect the foundation of the future building from heaving.

In accordance with this, the following measures are being taken:

Medium and coarse sand is used as a material for cushioning and filling the sinuses on the sides of the structure, because it allows water to pass through well.
A layer of geotextile under the cushion prevents siltation.
A drainage pipe, laid 20 cm below the base and at a distance of more than 1 m from the foundation, serves to drain excess groundwater.
The foam layer in the foundation serves to insulate heat and moisture.
The blind area performs a waterproofing function and reduces soil freezing in the immediate vicinity of the building.
Storm drains in the local area drain excess water.

Foundation options for heaving soil.

When carrying out construction on heaving soils, not every type of foundation can be used. The best solution is to use a non-buried or shallow foundation, which perfectly resists soil heaving during the frosty months.

Among such shallow foundations on heaving soils, strip foundations are especially popular, as they provide the necessary reliability and durability, and their construction is extremely simple and the cost is not so high.

A columnar foundation on heaving soils is used when the supports can be installed below the freezing point.

This allows you to save money on foundation construction while maintaining high reliability.

Scheme of a shallow foundation on heaving soils.

Such a foundation is placed if the site has loam, soils with close moisture, damp and swampy areas.

To construct a foundation on heaving soils, in this case, metal pipes with a cement-sand protective composition, reinforced concrete supports, asbestos-cement pipes, into which concrete mixture is poured, are used.

For construction on heaving soils, a pile version of the foundation can also be used, which, however, is not so popular. The fact is that its construction requires the use of special construction equipment, and this is an extra financial expense. This option is used only when the soil freezes to a depth of one and a half meters.

To make a structure on heaving soils from piles, materials such as concrete, reinforced concrete, and wood are used, which successfully resist heaving. Among the types that can be used, screw, cast-in-place, reinforced concrete simple and cast-in-place piles are recommended. A prerequisite for constructing a foundation of this type on heaving soils is the presence of an excellent drainage system.

Shallow strip foundation.

The non-buried strip foundation for heaving soil is a monolithic concrete strip with reinforcement in the form of a belt of metal rods. To properly install such a foundation for a house on heaving soils, several simple conditions must be met.

Scheme of a strip shallow foundation.

The initial stage differs little from the construction of the most ordinary foundation. You should dig a pit, the depth of which will be from 70 to 50 cm. After this, you will need to lay waterproofing material on the side slopes, which is usually ordinary roofing felt or plastic film.

Next, the pit on heaving soils must be filled with sand in layers, the thickness of each will be 20-30 cm. After filling, each sand layer is compacted. Next, formwork is placed from edged wooden boards. a layer in the form of waterproofing is laid on the sand, reinforcing metal rods with a diameter of 12 cm are installed. Such reinforcement will have two separate belts, each of which will have five rods and jumpers.

At the last stage, the shallow foundation is poured using a concrete mixture. The top layer of reinforcement is laid directly on the wet mixture (this is a feature that a non-buried foundation has for heaving soil). When connecting reinforcement elements, you cannot use a welding machine - only knitting wire, which provides higher strength and reliability.

Uneven shrinkage of structures on heaving soils.

Construction on heaving soils is dangerous because during the first winter period shrinkage and deformation of the foundation are possible. Among the frequently encountered ones it is necessary to note:

Cross-sectional diagram of a shallow strip foundation.

camber/sag: occurs due to uneven shrinkage. In this case, the most dangerous thing is the bending, which affects the condition of the roof and the stretching of the building area;
shear: occurs due to the subsidence of one part of the building and the rise of another. The most dangerous zone is the middle one, where the walls of the foundation and the structure itself begin to crack;
tilt: observed due to the rigidity of the structure for buildings with a relatively high height, but for the construction of which a shallow foundation was used;
distortion is a consequence of uneven shrinkage in individual small areas under the building;
horizontal displacement occurs at the foundations, individual sections of which are literally pushed out and moved during heaving.

Why do such uneven shrinkages occur on heaving soils? The fact is that when the soil freezes, the moisture contained in it freezes, its volume increases, and the soil begins to swell. The soil layers begin to rise, and if the construction was carried out without taking such features into account, the structure begins to deform and cracks appear on it. As a result, traces of destruction appear on the walls of the building.

To reduce such consequences, it is recommended to build on heaving soils using materials such as foam blocks, wood, brick, and concrete.

Foundation - slab, slab foundation

The walls of the house rest on a foundation slab

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 consumption of concrete make slab foundations the most expensive in private housing construction.

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

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.

The walls of the house rest on a shallowly buried strip foundation with a monolithic suspended floor slab on the ground.

It is necessary to distinguish

slab foundation and shallow monolithic strip foundation with suspended floors on the ground.

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

In this option, the monolithic reinforced concrete 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.”

A strip foundation with a monolithic suspended floor slab is 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 water protection measures aimed at reducing soil heaving deformations - ensuring a decrease in soil moisture, lowering the groundwater level, and draining surface water from the house

by means of vertical planning,
drainage structures,
drainage ditches, trays, trenches, etc.

Slightly buried foundations should be used 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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Calculation of the load, base area and thickness of the sand cushion of a shallow foundation

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Frost heaving of soil

Calculation for a shallow foundation.

An example of calculating shallow foundations on heaving soils should be given. For example, a one-story house is being built with the following dimensions:

height – 4 meters;
width – 5 meters;
length – 10 meters.

The structure includes two load-bearing internal walls, each 4 m high and 3 m long. The floor does not rest on the foundation and is filled with concrete. The base will have the shape of a tape with a base width of 40 cm and a depth of 70 cm. The foundation is made of reinforced concrete, for which reinforcement with a diameter of 12 mm is used. The frame will have two belts, each of which consists of five rods, jumpers with a length of 25 cm. Such jumpers are placed in increments of 50 cm.

To find out the mass that the strip foundation will have, you need to determine the following values:

Scheme of a shallow strip foundation on heaving soils.

Scheme of a shallow foundation with waterproofing on a printed pad.

geometric dimensions of the structure;
density of the building material used.

Geometric dimensions are quite easy to find out. So, the length of the foundation is equal to the perimeter of the future building, that is, you just need to calculate the sum of its sides:

The strip foundation will be poured not only under the external facade walls, but also under the internal load-bearing walls, so they are also taken into account.

Now you can find the volume based on the fact that the height of the tape is 70 cm and the width is 40:

V=36×0.4-0.7=10.08 cubic meters.

But this is the total volume from which the reinforcement must be subtracted to find out the amount of concrete. Knowing that the strip foundation has two belts of five rods with ligation, calculate the length for each:

The length of all belts will be equal to:

Each belt has five rods, which means their total length is: 62×5=310 m.

Now determine the length of the required jumpers for reinforcement:

Scheme of reinforcement of a shallow foundation.

For one upper chord the number of jumpers is:

Since the length of one jumper is 0.25 meters, the total length is:

For all horizontal frame lintels, the length is:

For vertical jumpers, take into account that there are 68 of them on one side and the same number on the other. That is, it turns out 136 pieces with a length of 40 cm. Their total length is:

Now calculate the total length of reinforcement required by a shallow foundation:

To find out the cross-sectional area for reinforcement, use the formula for the area of a circle:

Scheme for preparing concrete mortar for the foundation.

3.14×0.000036=0.00011 sq. meters.

To obtain the volume, use the formula:

0.00011×388.4=0.04 cubic meters meters.

Now we get the volume only for the reinforcement:

10.08-0.04-0.04=10 cubic meters meters.

The value of 0.04 is taken from the calculation that a shallow foundation will also be reinforced in the corners.

Using this not too complicated calculation, it is determined that a strip foundation on heaving soils requires:

10 cu. meters of cement (at a density of 2500 kg per cubic meter);
0.08 cu. meter of metal reinforcement (with a density of 7800 kg per cubic meter).

That is, the total mass of the entire foundation, which is erected on heaving soils in the form of a strip foundation, will be:

That is, the strip foundation has a mass of 25624 kg.

Building a house on heaving soils is not the best option. But if there is no other way out, then it is necessary to carefully calculate the future foundation so that after its construction the structure is not pushed out of the soil during winter heaving. This is not so difficult to do, but care must be taken to ensure that during operation there is no deformation of the foundation, and therefore the house itself.

Calculation of the flexibility index of building structures

1. Indicator of flexibility of building structures l

determined by the formula

,(1)

where EJ

— reduced bending rigidity of the cross-section of building structures in the foundation-basement-reinforcement belt-wall system, tf.m2, determined by formula (4);

WITH

— coefficient of foundation rigidity during soil heaving for the bases of strip foundations;

— length of the wall of the building (compartment), m;

,(2)

for columnar foundation bases

,(3)

Here pr

,
hfi
,
b 1
- the same notations as in paragraphs. - ;

f is the area of the base of the columnar foundation, m2;

- the number of columnar foundations within the length of the wall of the building (compartment).

2. The reduced bending rigidity of the cross-section of building structures in the foundation-basement-reinforcement belt-wall system, tf/m2, is determined by the formula

[EJ

] = [
EJ
]f + [
EJ
]z + [
EJ
]p + [
EJ
]
s
,(4)

where EJ f

,
EJ z
,
EJ p
,
EJ s
- respectively, the bending rigidity of the foundation, plinth, reinforcement belt, building wall.

3. Bending rigidity, tf/m2, of the foundation, plinth and reinforcement belt is determined by the formulas

=
g f Ef
(
Jf
+
Ayc2
);(5)

=
g z Ez
(
Jz
+
Azyz2
);(6)

=
g p Ep
(
Jp
+
Apyp2
);(7)

where Ef

,
Ez
,
Ep
- respectively, the deformation modules tf/m2, the foundation material, the base and the belt;

,
Jz
,
Jp
- respectively, the moments of inertia, m4, of the cross-section of the foundation, plinth and reinforcement belt relative to its own main central axis;

,
Az
,
Ap
- cross-sectional area, m2, of the foundation, plinth and reinforcement belt;

y ,
yz , yp
- respectively, the distances, m, from the main central axis of the cross-section of the foundation, plinth and reinforcement belt to the conditional central axis of the cross-section of the entire system;

g f ,
g z , g p
are respectively the coefficients of the operating conditions of the foundation, plinth and reinforcement belt, taken equal to 0.25.

The bending rigidity of a foundation consisting of blocks not connected to each other is assumed to be zero. If the base is a continuation of the foundation or their joint work is ensured, the base and foundation should be considered as a single structural element. In the absence of reinforcement belts EJ p

= 0. If there are several reinforcement belts, the bending rigidity of each of them is determined by formula (7).

4. Bending rigidity, tf/m2, of walls made of bricks, blocks, monolithic concrete (reinforced concrete) is determined by the formula

s =
g s Es(Js + Asys2),
(8)

where Es

— deformation modulus of the wall material, tf/m2;

g s

- coefficient of wall operating conditions, taken equal to: 0.15 - for walls made of bricks, 0.2 - for walls made of blocks, 0.25 - for walls made of monolithic concrete;

— moment of inertia of the cross section of the wall, m4, is determined by formula (9);

A s

— cross-sectional area of the wall, m2;

y s

— distance, m, from the main central axis of the cross-section of the wall to the conditional neutral axis of the cross-section of the entire system.

The moment of inertia of the cross section of the wall is determined by the formula

,(9)

where J 1

and
J 2
- respectively, the moment of inertia of the wall section along the openings and along the piers, m4.

The cross-sectional area of the wall is determined by the formula

,(10)

where bs

— wall thickness, m.

The distance from the center of gravity of the reduced cross-section of the wall to its lower edge is determined by the formula

,(11)

5. The state from the main central axis of the cross section of the foundation to the conditional neutral axis of the foundation-basement-reinforcement belt system - wall is determined by the formula

,(12)

where Ei

,
Ai
are, respectively, the deformation modulus and cross-sectional area
of the i
-th structural element (basement, wall, belt);

— coefficient of operating conditions
the i
-th structural element;

— the distance from the main central axis of the cross-section of
the i
-th structural element to the main central axis of the cross-section of the foundation.

6. Bending rigidity, tf.m2, of panel walls is determined by the formula

,(13)

where Ej

,
Aj
are, respectively, the deformation modulus, tf/m2, and the cross-sectional area, m2, of
the j
-th bond;

— number of connections between panels;

— distance from
the j
-th connection to the main central axis of the cross-section of the foundation, m;

- the distance from the main central axis of the cross section of the foundation to the conditional neutral axis of the foundation-wall system of the building, determined by the formula

,(14)

in which n

— the number of structural elements in the foundation-wall system.

Shallow foundation on heaving soils: types of foundations and their features.

Shallow strip foundation on heaving soils.
Heaving 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 out 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 a shallow base that will not be subject to uneven shrinkage. In addition, such a base can perfectly cope with all loads. It is best to build a shallow foundation on heaving soils. This is exactly what we will discuss in our article.

Criteria for choosing a foundation type

High level of reliability
Increased strength
Ability to work with any type of building
Possibility of completing construction in a short time

Main disadvantages:

Long period of time for excavation work
Large mass of materials
High cost of materials
Difficulty of work

When installing a foundation on piles, one must take into account its main positive and negative features.

Pros:

Minimum amount of building materials used
Affordable price
Low shrinkage of materials
Ease of execution
Possibility of installation in the most difficult areas

Minuses:

Of the main drawbacks, only one can be identified - when carrying out work, it is necessary to use specialized equipment.

The materials for installing piles can be wood, concrete, or reinforced concrete sheet.

Types of piles. They are divided depending on the installation methods in the ground:

Driven type piles. They are pre-fabricated and then lowered into the soil.
Printed look. Installation is carried out directly in the ground in a special channel.

Piles are also classified according to their condition in the soil:

Rack. Installed in dense soil. Applies additional pressure on the ground
Hanging view. Installed in cases of low soil density.

To achieve high efficiency, it is recommended to use wooden piles. However, when installing them, the characteristics of the soil should be taken into account. With constant humidity, the equipment will quickly deteriorate and its service life will be reduced.

To increase service life and achieve maximum strength, it is recommended to use reinforced concrete piles. They are not subject to destruction due to humidity, but are in a high price category.

How can you build a foundation on heaving soil?

Arrangement of a shallow strip foundation on heaving soils.
Arranging a foundation on moving types of soil is an undesirable option. This is due to the fact that there is a sufficiently large heaving force that can lift 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 loose soil with sand. This is done right up to the freezing point. Although this option is the most effective, its cost is too high, so its use in many cases is impractical. There is also another method, which involves the use of a type of foundation that will lie at a sufficient depth to reach the freezing point. This refers to columnar and pile foundations on heaving soils. Heaving will not be able to influence such grounds, but there is a significant drawback here too. It lies in the fact that in many cases such foundations entail considerable costs.

But you can resort to a third option, which is to use a shallow foundation. Its use allows you to ensure reliable stability of the building. This type of foundation can effectively resist ground movement. Thanks 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 from monolithic reinforced concrete structures.

Construction of a shallow foundation on heaving soils.

Such a foundation base 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. During the mixing process, experts recommend adding a hydrophobic compound to the concrete mixture, which can improve the stability of the structure. After completing the construction of the foundation, care should be taken to create a drainage system. We also do not forget about reinforcement when arranging the foundation.

Types of bases for moving soil.

In the process of carrying out construction work on moving types of soil, not all types of foundations can be used. The best option in this situation is a shallow foundation for the house. It is able to effectively resist soil heaving processes that prevail in the cold season. If you look at the choice of shallow foundations for moving types of soil, then the strip foundation has gained the most popularity. It has a number of advantages, among which the main ones are the following:

Shallow strip foundation on heaving soils.

The LF base can provide the required durability and reliability of the structure;
The construction of such a foundation is characterized by ease and simplicity;
Relatively low construction costs.

We also note other types of foundations that can be used on moving soil. This may include a pile foundation, but at present it is not particularly 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 as a whole. 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 production process of support-pile structures, various materials are used that resist heaving processes. This includes concrete, reinforced concrete elements, and wood. It is also necessary to equip a reliable drainage system.

Shallow columnar foundation on heaving soils.

A shallow columnar foundation is also used. Its use is relevant in cases where supports can be installed below the soil freezing level. Thanks to this, the financial costs of arranging the foundation are somewhat reduced. At the same time, excellent reliability still occurs.

A columnar type foundation is used in the presence of loam, soil with nearby groundwater, and also in wetlands. To construct this type of foundation 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.

Stages and features of construction

The construction of the MZLF begins with design, as well as site preparation (removal of construction debris and leveling of the surface).

Construction stages:

marking the area using pegs and ropes;
digging a pit up to 1 m deep;
laying waterproofing materials (for example, roofing felt or film);
filling with sand and compacting the layer up to 30 cm;
construction of wooden formwork, reinforcement frame;
pouring a concrete mixture (for baths choose concrete grades not lower than M200, for houses - not lower than M300);
laying the upper reinforced mesh on the still wet mixture;
laying a heat-insulating layer (for example, extruded polystyrene foam) on hardened concrete;
filling the insulation with sand and compacting it;
If it is necessary to drain water, install a blind area.

The construction of the MZLF is carried out in the warm season. If construction is forced to stop for a period of cold weather, then conservation is carried out.

Shallow-depth strip base.

A strip foundation on heaving soils is essentially a monolithic concrete strip. It is equipped with a reinforcing belt, which uses steel rods. To properly install such a foundation, several steps must be completed, each of which we will consider below.

The initial steps here are approximately the same as when constructing a standard 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 plastic film or roofing felt.

Designing foundations on heaving soils involves arranging a sand cushion at the bottom of the pit. It consists of several layers of sand twenty centimeters thick. After each layer has been filled in, it must be compacted thoroughly. Then the formwork structure is constructed from the board. A waterproof layer should be laid on top of the sand cushion, and reinforcing steel rods with a diameter of 12 centimeters should be installed.

As part of the next, final stage, it is necessary to fill the shallow foundation on heaving soils with concrete mortar. The top reinforcing layer is installed on the raw mixture. In the process of combining reinforcement components, you should abandon the use of a welding machine. The technology involves the use of knitting wire.

How to build a monolithic strip foundation for a barn

An example of a finished trench filled with sand as a cushion

Considering that the overall dimensions of such structures are small, the excavation work here is minimal. As a rule, the construction of a monolithic foundation consists of several stages:

Development of a sketch drawing of the future building;
Marking the construction site taking into account the dimensions of the foundation slab, its thickness and dimensions;
Digging a pit to a depth of 60 cm, there is no point in doing more due to the high strength of the slab and the uniform distribution of the mass of the structure;
The bottom of the trench must be carefully leveled, compacted and a sand and gravel cushion placed on the bottom. It also needs to be compacted so that the thickness of the pillow is no more than 15-20 cm. To facilitate compaction, the pillow can be pre-moistened with water.
On the sides of the finished foundation pit, it is necessary to install formwork in which the internal overall dimensions correspond to the specified parameters of the foundation. Align the finished formwork horizontally and vertically.
Now you need to make high-quality reinforcement of the pit. For this, a metal mesh with dimensions of 8 mm is used; you can use a smaller one, only then you need to reduce the interval between the rods. It is recommended to connect it with formwork, but this is often not practiced in order to build a foundation in a much shorter time.
Now you need to fill the pit with liquid concrete, carefully level and compact it. If necessary, the top edge must be leveled with liquid concrete using a hydraulic level.

The monolithic strip foundation for the barn is ready. Now all that remains is to wait approximately 3-4 weeks until the concrete gains grade strength and you can begin to build load-bearing walls using foam blocks or other heavy building materials.

Shrinkage of buildings on moving soils.

The construction of structures on heaving soil types threatens with possible shrinkage, as well as deformation processes directed against the foundation. Commonly encountered ones include the following:

Deflections and bends due to uneven shrinkage. In this case, bends are much more dangerous, since they can affect the condition of the roof.
Shifts. The construction of a foundation on heaving soils may be subject to shifts caused by the rise of one side of the building and the rise of the other.
Distortions - formed due to uneven shrinkage in some places under the structure.

Many people ask questions about why such uneven shrinkage occurs. This phenomenon is caused by the fact that as a result of soil freezing, the moisture contained in it also freezes. And this, in turn, leads to an increase in its volume. As a result, the soil swells. Further, entire layers of soil can rise, which leads to deformation and destruction of the building.

These processes negatively affect the constructed building only if it was built without taking into account the characteristics of the soil. Therefore, shallow foundations should be installed. As we have already indicated in the article, in addition to a shallow strip foundation, pile and pillar foundations can also be used. The main thing is to strictly follow the technology, and destructive processes will not affect your building.

Recommendation: A good general article. Reveals the main points of a shallow foundation on heaving soil. Before you dive headfirst into building your foundation without losing your money, you will still need to study and understand this topic in more detail.

Foundation on heaving soils: construction features