Shallow strip foundation. Types of shallow foundations and laying technology. Final stages of work

An economical and at the same time the most reliable foundation is the dream of every beginning developer. But is this option possible? Quite. A direct confirmation of this is the shallowly buried strip base. Arranging such a foundation does not require large financial and time expenditures, but the result of the work is very pleasing - you get a high-quality and durable foundation. Moreover, you can even build it with your own hands, without the involvement of professional builders. To make sure of this, let's look at each stage of constructing a shallow foundation. In addition, we recommend watching the installation video - it will allow you to understand the technology of laying the base in even more detail.

Before we begin to analyze the laying technology, we will outline the main features of the shallow-type strip base:

• is a frame in the form of a monolithic reinforced concrete strip, outlining the perimeter of the future building;
• costs half as much as a deep foundation;
• suitable for the construction of one-, two- and three-story buildings made of wood, concrete, stone and brick;
• can be used on non-heaving areas, as well as on weak, medium and highly heaving soil;

Important! In the last two cases, it is necessary to ensure high-quality soil drainage.

• arrangement involves a minimum amount of land work;
• makes it possible to build a small basement or cellar within the perimeter of the building;
• You don’t need to use special equipment for installation.

A shallow foundation cannot be built on frozen ground, so all work must be completed before the frost arrives. Laying the base is carried out in four stages.

Foundation arrangement

Stage 1: Preparation of trenches

The first step is to prepare the trenches into which concrete will subsequently be poured.

First, mark the site on which the foundation will be located. Then accurately determine the corners of the future structure - they should be as even as possible. Next, proceed to creating the base - dig trenches around the perimeter of the marked area. The optimal foundation depth is 50 cm. The width of each trench should be at least 60-80 cm.

When the holes are dug, you need to compact the soil - arrange a special cushion on it. If the base of the site is silty fine sand, the soil must first be covered with geotextile - it will prevent siltation of the site and protect the foundation cushion from weeds, which are likely to grow in it due to high humidity.

Preparing the trench

The pillow itself should reach a height of 30-50 cm - this will be enough to give the foundation the necessary strength. First, sand is poured in a layer of 15-20 cm. It must be thoroughly moistened and compacted. Then fill in 15-20 cm of gravel. Wet and compact the base again. Next, waterproofing is carried out - sheets of roofing felt are laid.

When the work is completed, check the level of the resulting base surface - it must be strictly horizontal.

Stage 2: Arrangement of formwork

The next step is working with formwork. To build it you will need a large number of boards. Keep in mind that when pouring concrete on the formwork there will be serious mechanical impacts, so stock up on a strong board - its thickness should be at least 5 cm.

The boards need to be knocked down in the form of shields. The optimal connection step is 80 cm. If the step is wider, the structure will not be strong enough. Finished wooden panels can be fixed to the base using supports or support beams. The latter need to be installed every 60-70 cm. The recommended cross-section of the beams is 50x50 mm. The shields must be tightly fixed between installed beams or supports. After installing the formwork, cover the panels with thick polyethylene or glassine.

It is also advisable to strengthen the formwork structure from the outside with special supports so that it does not deform during subsequent installation work.

Stage 3: Base reinforcement

High-quality reinforcement is the key to the integrity and durability of the entire structure of a shallow foundation, so this step should not be skipped under any circumstances.

Reinforcement

First, build a reinforced frame. To do this, prepare metal rods 14-18 mm in diameter. Their length can be any, but experts recommend using long products - 2-5 m. Remember: the longer the rods, the fewer connections and the stronger the foundation. Metal products are laid along the entire perimeter of the foundation on a cushion, thereby forming a frame.

To arrange a reinforced skeleton, rods of a smaller cross-section are usually used - up to 10 mm. The length of the products should be slightly wider than the trench. All reinforcement is installed strictly perpendicular to the frame elements. They can be connected in two ways: the more reliable is electric welding, and the more affordable is wire ligation. The latter must be very flexible so that it is easy to work with.

Advice. For ease of installation of the reinforcement skeleton, you can use scraps of plastic pipes: saw them on a circular saw to make rings 5 ​​cm high, install the resulting products on the base and fix the reinforced structure on them.

Stage 4. Pouring concrete

The most important stage is the actual pouring of the foundation. It can also be divided into several stages:

1. Preparing the mixture. If you are laying the foundation yourself, you will probably decide to prepare the concrete mixture yourself. There is nothing complicated about this. The main thing is to buy high-quality consumables: concrete itself, crushed stone and sand. It is desirable that the latter be of a large fraction - it adheres better. The mixture is made from concrete, sand and water in a ratio of 1:3:1. After thorough mixing, 5 parts of crushed stone are added to the composition.
2. Pouring the mixture. When the composition is thoroughly mixed, you can pour it into the prepared trenches. To prevent air pockets from forming when the foundation hardens, the concrete must be compacted after laying. This can be done either manually - using a wooden tamper, or using a special vibropress. The composition must be poured not at one time, but as it is compacted. As the concrete dries, check its level regularly.
3. After the foundation has completely hardened, fill the remaining layers between the foundation trenches with soil and compact it.

Pouring concrete

As you can see, equipping a shallow strip foundation with your own hands is really not difficult. Adhere to the general technology and follow the installation rules that professional builders have long established - compliance with these two conditions will lead you to a positive result, even if this is your first time pouring a foundation.

Shallow strip foundations have become popular for the construction of private houses due to their versatility and the ability to install them without the use of heavy equipment and for relatively little money. How to properly build a shallow strip foundation with your own hands?

When is MZLF used?

A shallow strip foundation (MSLF) is a type of strip foundation with a laying depth of no more than 70 cm. This type of foundation has become widespread in individual construction due to several significant advantages:

• relatively low cost,
• small volume of earthworks,
• no need to use heavy equipment,
• applicability on different types of soil,
• low cost of building materials.

It is possible to build houses of up to 3 floors from timber, logs, frame, brick with lightweight masonry, and foam concrete.

A shallow foundation is suitable for both non-heaving and heaving soil. It cannot be done on biogenic soils: peat, sapropel, or clay.

Types of MZLF

A shallow strip foundation can be either monolithic or prefabricated. A monolithic foundation is a reinforced concrete strip, which is located around the perimeter of the building and under the load-bearing walls. In the case of a precast foundation, this strip is made from foundation blocks held together with cement mortar. It will take much less time to create a prefabricated foundation, but its service life is shorter than that of a monolithic one.

A combination of pile and strip foundation - a shallow pile-strip foundation. In this case, the tape rests on screw or bored piles, and a sand or crushed stone cushion is made under it. Pile foundations are made on difficult soils or when there are differences in elevation on the site.

Construction order

Before making a shallow strip foundation, it is necessary to conduct a geodetic examination to find out

• soil composition and quality,
• the depth of its freezing,
• ground water level.

These parameters influence the choice of foundation type and its depth. However, if you want to save on expensive expertise, to assess the quality of the soil, it is enough to drill holes in several places on the site.

• Clay soil can be rolled into a ball by hand.
• Loam can also be rolled into a ball, but it will have cracks.
• The sandy loam soil will partially crumble.
• It is impossible to roll sandy soil into a ball.

The construction site must be cleared of debris and plants, trees must be uprooted, and the fertile layer of soil must be removed.

Next, markings are made - the dimensions of the house are transferred to the site. To do this you will need rope and pegs. First of all, note the front wall of the house, which faces the street. Next, two other walls are built perpendicular to it. To check whether the rectangle is even, compare its diagonals. There are beacons in the corners. At a distance of about a meter from this contour, a blind area of ​​boards is installed, onto which ropes are pulled, showing the dimensions of the strip foundation. You can mark the dimensions directly on the ground with lime mortar.

After this, they dig a trench. Its depth is equal to the thickness of the tape plus the thickness of the sand cushion. The thickness of the cushion is usually 20 cm. Typically, a trench for a shallow strip foundation is made 0.5 m deep and 0.6-0.8 m wide.

Under heavy structures, such as a stove, porch, stairs, pits are dug.

The pillow is made of sand, crushed stone or a mixture of them, 30-50 cm thick. A common option is also a two-layer pillow: 20 cm of crushed stone and 20 cm of sand. If the soil in the area is dusty, then before filling the cushion, you need to lay geotextiles in the trench.

The pillow is poured in layers, compacting each layer. If it is two-layer, first pour 10-15 cm of sand and compact it. To make this task easier, the sand is moistened. Next, gravel is poured in and compacted as well. The surface of the pillow must be strictly horizontal; this can be checked using a level. A waterproofing material - roofing felt - is laid on top.

Monolithic MZLF

Next, the formwork is assembled. It uses boards or panel materials such as plywood, OSB and others. The board must be at least 5 cm thick. The boards are knocked down into shields. The formwork should be several centimeters higher than the expected concrete level. The height of the tape above the ground surface should be less than or equal to the depth and equal to 4 times the width of the tape.

The shields are fixed with pegs and connected to each other with self-tapping screws or nails. Fastening elements should not protrude into the formwork. If they end up in the concrete, cracks may appear or even a piece of concrete may break off. Also, the formwork for a shallow strip foundation is additionally strengthened with inclined supports (struts) made of timber with a cross-section of at least 5 cm. The supports are placed on the outside at a distance of approximately 0.5 m. It is necessary to drill holes in the formwork for communications. Pipes are inserted into them.

The inside of the formwork is lined with polyethylene for waterproofing and reducing adhesion to concrete. You can also use permanent formwork made of extruded polystyrene foam.

Reinforcement

The construction of a shallow strip foundation necessarily includes reinforcement. The reinforcement is knitted with knitting wire. The use of welding to connect rods is not recommended, as corrosion is most likely to occur in these areas. Reinforcement diagrams are shown in the figure.

The minimum number of rods for the frame of a shallow strip foundation is 4 pieces. Longitudinal reinforcement must be class AII or AIII, have a ribbed section. The longer it is, the better - each connection reduces the strength of the frame. For transverse parts, thinner smooth reinforcement (6-8 mm) is used. For a shallow foundation, two reinforcing belts are sufficient, a total of 4 longitudinal rods. The reinforcement should be 5 cm from the edges of the foundation. There should be 30-40 cm between the vertical jumpers.

It is especially important to properly reinforce the corners. To do this, the rods are bent in such a way that the approach to the other wall is at least 40 times the diameter of the rod. In this case, near the corners the distance between the vertical jumpers should be half as much as in the wall.

Fill

It is better to take factory-made concrete, grades no less than M200 (for wooden houses) and M250 (for brick houses). When making it yourself, it is better to mix concrete not by hand, but in a concrete mixer.

It is advisable to fill the entire foundation in one go. Concrete is poured in layers, each layer is leveled and compacted. For this purpose it is better to use a vibrating rammer. The last layer is leveled according to the mark applied to the formwork. Professional builders who have already made dozens of foundations recommend sprinkling dry cement on top of the concrete. This is necessary so that the top layer sets faster. The foundation hardens for about a month.

Anti-heaving

Before you make a shallow shallow foundation on loam, you need to know that such soil requires anti-heaving measures:

• drainage,
• waterproofing,
• insulation.

For more information about foundation insulation, watch the video:

Important! It is very advisable to complete the entire cycle of work (build the house completely) in one season, so that the foundation does not remain without load during the winter. Otherwise, the forces of frost heaving can squeeze the foundation out of the ground, deform or break it. If it is not possible to complete the house before the cold weather, then the ground around the foundation must be covered with any heat-insulating material (straw, sawdust). There is no need to remove snow on the site.

MZLF on stilts

Foundations on piles are made on difficult soils. For this purpose, screw or bored piles are usually used. A sand cushion is poured under the tape. It will resist soil heaving.

Bored piles are made directly on the site. To do this, they drill wells, place pipes and reinforcing frames in them, and fill them with concrete. The depth of the wells should be below the soil freezing level.

The pile reinforcement must be connected to the tape frame. To do this, it must rise above the base of the tape by at least 40 cm. If screw piles are used, then holes are drilled in them, reinforcement is threaded through them and connected to the frame of the tape.

A shallow strip foundation, either monolithic or prefabricated, can be made independently. It can be used to build houses from different materials and different number of storeys (up to 3 floors), and it is used on different types of soil.

Usually, when private buildings with a small number of floors are built from lighter materials (bricks, aerated concrete blocks, foam concrete, etc.), a strip foundation is used at shallow depths. This solution is beneficial in terms of economy and practicality.

For such a foundation, a pit is created for a brick house or for a house made of aerated concrete. It goes deeper below the soil freezing mark. In the Urals and Siberia, and in other areas with severe cold, it deepens below 150 cm. And in such an area it is necessary to work with heavy equipment. This foundation covers the perimeter of all load-bearing walls. Its construction is only in exceptional cases lower than 150 cm. SNiP for this type of foundation is calculated from the load of the walls per area. The bearing capacity or characteristics of the soil in a particular area are also taken into account.

Advantages of this foundation:

1. Ease of work.
2. Good cost savings.
3. There is no need to use special equipment (it is only needed in the specified regions).
4. Excellent strength if a small building of 1-2 floors is being erected.
5. Makes it possible to insulate semi-basement rooms.
6. A wide range of materials and technological solutions for its construction.
7. It can be created as a monolithic type, where concrete is poured.
8. Its other configurations are bricks or concrete blocks.

The design of such a foundation:

1. Weak strength for buildings on heaving soils. The dilemma is solved thanks to sand filling and a drainage system. This reduces the impact of the soil.
2. Impossibility of creation on frozen ground.
3. It cannot be left unloaded during the winter.
4. Points 2 and 3 determine the short time frame for pouring it and erecting walls: about 4-5 months.

Learn more about monolithic strip foundations and slabs

There are several types or subtypes for MLF. Let's list everything:

1. Ribbon belts. Without recesses, suitable for frame houses and light structures. The peculiarity is that the width is always greater than the height. This will make the supporting surface much better.
2. Non-recessed tape. Ideal for wood structures. Feature: the base belt is raised.
3. Shallow LF. Let's analyze its device more carefully. Can be used for any type of building, both log and stone.
4. Recessed is, in fact, a monolithic slab, because it is poured below the freezing level. Suitable for absolutely any structure.

For your information! Any type or type of MLF cannot be put into operation without drainage, waterproofing and backfilling with sand.

Stages of creating a strip foundation at shallow depths (LFMG)

When working on heaving soils, it is necessary to insulate the soles of the working tape of this foundation. In conditions of sand and sandy loam, it is fashionable to insulate only the blind area.

Step-by-step instruction:

1. Calculation of tape width and reinforcement section, creation of a reinforcement project.
2. Creating a trench if a house without a basement is being built.
3. A pit is dug if a base is planned.
4. Laying drains to remove runoff.
5. Warming of the sole.
6. Creating a substructure.
7. Installation of formwork.
8. Laying of reinforcement.
9. Pouring concrete. The organization of communications and ventilation ducts is provided.
10. Waterproofing of all edges of the tape after dismantling the formwork.
11. For a functioning basement, the outer walls are insulated with tape.

Determination of soil composition

This procedure can be performed without specialists. Just dig holes in different places. Examine the soil visually. Here's how to do the test:

1. It easily forms into a dense ball and does not collapse when pressed with your fingers. These are signs of clay.
2. If it cracks under pressure, it is loam.
3. If it has partially crumbled, it is sandy loam.
4. It didn't turn out to be a ball at all - it was sand.

Calculation of tape width

Here the total load is calculated. It includes the weight values ​​of all structures:

• base;
• floors;
• walls;
• roof;
• facing;
• insulating materials;
• partitions;
• furniture;
• living people;
• loads from wind and snow.

Wind and snow data is obtained from the weather report for your area. Typically, a width of 40-50 cm is sufficient to create a strong tape even on difficult soils.

Calculation of depth

Here are the rules:

1. A depth of 40 cm is suitable if there is protection against heaving.
2. 45 cm – subject to sandy soil; groundwater is low.
3. 50 cm – when the clay freezes to 100 cm.
4. 75 cm – clay freezes to 150 cm.
5. 100 cm – freezing at 250 cm.

There are ways to protect against swelling in winter:

1. Under the sole the soil is changed to non-metallic material. Minimum layer – 40 cm.
2. Drainage is created around the perimeter.
3. A blind area and storm drain are installed on the surface.
4. The sole and blind areas are insulated.

Insulation project:

The following numbers will help in the question of how much the tape should be raised above the ground:

• for the base, the tape is buried in place and rises 170 cm above the surface;
• for a modest technical underground, a height of 40 cm above the ground will do;
• to create floors on the ground, the tape is at the same level with the ground or exceeds it by 20 cm.

Advice! Any of these options allows for normal two-layer reinforcement inside the tape. At the same time, you can still arrange a protective layer of 1.5 - 4 cm.

It is advisable to use a calculator when making calculations:

Marking

At the building site, you need to tighten the cords. They are located along the outer and inner perimeter. There is no need to remove the axes here, as when working on columnar or pile foundations.

Positional criteria for marks and cords.

1. The starting angle of the main facade is positioned 3 m from the site line, 5 m from the axial border of the street.
2. To mark the wall of the main facade, two cords are pulled over the cast-offs. A 60-80 cm strip is placed between the pegs. These cords also reflect the edges of the foundation.
3. For each wall, a right angle is determined. After which the side walls are calculated. Here the work follows the triangle method. They also require pulling the cords over the cast-offs.
4. The rear façade and interior walls are determined using the same method.

A level is used to align the horizontal lines of all castoffs in a single plane. Correct positions of the cords: 5-7 cm below the top side of the formwork.

Also, the tape trenches must provide for the location of insulation, drainage, and access to the external walls of the tape. To do this, the width of the trench develops 50–80 cm inside the perimeter of the building, 80–120 cm outside.

For excavation work, you can only draw the contours of the trenches. This is done on the soil using lime mortar. If there is a base, a pit is dug out. The cast-offs in the corners should not interfere with the removal of soil, which is carried out by special equipment.

Substrate made of sand or crushed stone

Typically the substrate is formed from:

• sand, layer 20 cm, it is treated with water or compacted with a vibrating plate;
• crushed stone, the same layer, it is manually bayoneted in layers or similarly compacted.

Example of a sand cushion

The crushed stone layer covers the sand layer

At this stage, drainage is installed along the entire strip perimeter. They should be flush with her sole. The drains are looped into a single circuit. This results in one slope towards the underground compartment where wastewater will accumulate.

With a 40-centimeter immersion of the foundation, it is possible to get rid of heaving. To do this, line the outer side of the tape with polystyrene. Required layer – 5 cm. Width – 60 cm.

When the foundation is 70–100 cm deep, it is necessary to insulate the blind area. Insulation is carried out at a level of 30-40 cm. Heaving impulses are not completely eliminated, but are reduced significantly.

Formwork

As a rule, the following materials are used to create shields:

1. Edged board. The minimum thickness is 5 cm. Its advantages are that it can be reused. Disadvantage: assembly takes a lot of time.
2. Plywood with many layers. Its advantages: powerful resistance to moisture, strength. The downside is the huge price.
3. OSB. Pros: can be used after the formwork has been dismantled, strong moisture resistance, retains geometry.

For your information! Crossbars are placed at the level of the formwork, and the cast-offs are pulled out. This way the formwork is level, both horizontally and vertically.

Example in the photo:

It is important to know! In areas of connections in shields, gaps larger than 2 mm are not allowed. The concrete base is poured without formwork. Its functions are performed by the walls of the trench.

Formwork installation options:

1. Removable. The top side of the boards exceeds the design mark by 5-7 cm. The walls inside are insulated with extruded polystyrene foam.
2. Fixed. Polystyrene blocks are used for assembly. The rigidity of the structure is determined by the jumpers.

The first option is more popular, because after pouring, water protection is installed on the surface. Then insulation is laid on it.

An example of placing and strengthening formwork:

Screeds are used for vertical fixation of panels. Required pitch: 50 – 100 cm. Holes are placed inside the ties at different heights. The cartridges will pass through them. And in the underground side, engineering technologies will be introduced through such pipes. Above ground level, the holes will become ventilation ducts. Through them, moisture will leave the underground.

Reinforcement and filling

Foundations built on heaving soils experience impressive loads. For this reason, reinforcement is carried out at the edge of the tape at the top and near its bottom. The rods are protected from corrosion. The thickness of the protective layer should reach at least 1.5 - 4 cm.

To reinforce the monolith, rods of 8-16 mm are used. This is a periodic longitudinal section. it becomes stiffer if rectangular clamps are attached to it. They are formed from smooth reinforcement with a parameter of 6-8 mm.

One of the popular reinforcement schemes:

Independent calculation of reinforcement is based on the cross-section of the tape, taking into account 0.1% of the reinforcement from the total area. Calculation methods:

1. The total cross section is calculated. The height of the tape (H) is multiplied by its width (W) and divided by 100 (calculation is in mm). Formula: H x W: 100.
2. The cross-section of the longitudinal rod is determined from the reinforcement diagram sheet.
3. The adjustment takes into account a 4 cm layer of protection, according to the criteria of SP 52.101. THAT is, the maximum number of rods in a row is 40.
4. The thickness of the clamps should be a quarter less than the main rods.

Example of corner reinforcement

Wire is used to tie the frame. It can be tied mechanically or manually.

Example of reinforcement of interface sections

Reinforcement criteria for this foundation:

1. The overlap is spread in adjacent lines of one belt by at least 60 cm.
2. The length of the overlap is equal to 50 rod diameters.
3. In areas where walls meet and at corners, joints of rods are not allowed. One rod is bent there and ends up on the adjacent side by 40-60 cm. Then it is overlapped with the next part of the reinforcement.

Criteria for independently creating a concrete composition.

The elements of concrete mortar are classic: crushed stone, sand and cement. Each brand of cement has its own mixing proportions:

M 300: crushed stone - 3.7 shares, sand - 1.9 shares, cement - 1 share.

M 250: 3.9 (crushed stone), 2.1 (sand), 1 (cement).

M200: 4.8 (w), 2.8 (p), 1 (c).

M150: 5.7 (w), 3.5 (p), 1 (c).

M100: 7 (sch), 4.6 (sand), 1 (c).

Mixing should only be done in a concrete mixer. The time of this operation is 1.5 minutes. You can add various additives to improve the quality of the composition. Grade M100 should be used only for footings.

An example of laying engineering sleeves in formwork:

The filling criteria are:

1. The composition is laid one vector at a time in layers. Each layer is 40-60 cm. It is compacted with a vibrating tool.
2. The formwork is filled in one session.
3. Allowable pauses are 2 hours, no more.
4. The composition is poured from a height of 50 -200 cm above the formwork.
5. The vibrating tool attachment is placed in the composition for 2-10 seconds. Air bubbles should disappear.

Concrete maintenance and formwork removal

When the composition in the formwork has strengthened by 50-70%, maintenance of the concrete is necessary. Here you will need the following operations:

1. It is covered with a film that creates protection from precipitation and excessive moisture.
2. A heat cable is laid into it, a warm formwork or a layer of straw is installed. This protects the concrete from freezing. This is especially true in winter.
3. The concrete is covered with a tarpaulin and watered from a watering can. There should be a diffuse stream. The operation is performed in the first three days after filling. This protects the concrete from active evaporation.

These actions help eliminate the appearance of cracks, shrinkage, and internal stresses. In hot weather, concrete should be moistened after 8 hours. Maintenance of constant compress conditions is required.

Removal of formwork can be done in accordance with air temperatures:

At +30, removal 4 days after pouring,

At +20 – after 8 days,

At +10 – after 14 days

At +5 – after 28 days.

After removing the formwork, waterproofing is installed on the sides of the foundation. Photo example:

Methods for waterproofing a monolith:

1. Applying 2-3 layers of bitumen mastic.
2. Pasting with roll polymers.
3. Treatment with penetrating compounds.

The outer walls of the foundation should be insulated along their entire height. Bitumen mastic is used to attach the insulation. Then the blind area is insulated around the circumference of the foundation.

If there is high ground water in the area, drainage is created.

Example of a completed foundation:

What will a private builder say?

Judging by the reviews of the owners, the positive ones include:

1. Reasonable price.
2. Just install it yourself.
3. Reliable.
4. Suitable load-bearing capacity for popular aerated concrete structures.

Here is how the owners respond, understanding the shortcomings:

1. Not designed for heavy real estate objects above two floors.
2. Questionable durability of the structure.

Price aspect

Today, the creation of this foundation costs in the range of 100,000 – 250,000 rubles. The amount is determined by its parameters, expenses on materials, tools, equipment, work (if workers are hired).

Foundation in four days

The video below is the first part in a series of materials on creating a competent shallow strip foundation in a short time.

Strip foundation is the most common type of foundation
for building a house. Therefore, everything is clear with him, but here’s how he differs from him
shallow (MZLF) - shallow foundation, how to calculate and how
do?

Shallow strip foundation (shallow) MZLF

Characteristics - design principle

Shallow strip foundation or simply MZLF according to
The installation method is similar to its counterpart, but has important differences:

• foundation laying depth up to 700 mm;
• located above the soil freezing zone;
• designed for installation on swollen (heaving)
  soils.

The main feature of a shallow strip foundation
is that it makes it possible to level out frost heaving
soil. This is due to the fact that despite the general rigidity of the MZLF design,
together with the weight of the entire structure, moves up and down depending on time
of the year. Since the foundation is not deeply deepened, but moves evenly, then
therefore, it is not destroyed by such vibrations.

Schematic diagram of a shallow strip foundation

Shallow strip foundation - diagram

1. Sand and gravel cushion
2. Foundation tape
3. Waterproofing layer
4. Vertical (or coating) waterproofing
5. Fittings (diameter 12)
6. Fittings (diameter 8)
7. Base
8. Wall

Where can it be used - application

Shallow strip foundation is suitable for
construction of low-rise residential buildings and other structures from those materials
which will not create significant pressure on the base of the foundation. To such
structures and materials include:

• log cabins;
• cellular concrete - foam concrete, gas silicate blocks;
• lightweight bricklaying;
• frame-panel buildings.

When arranging a foundation of greater width, heavy houses made of timber or logs can be erected on it. But in this case, the soil will freeze to a shallower depth and there is a possibility of deformation of the foundation. Thus, if you plan to build a monumental building, it is better to equip a strip monolithic foundation.

However, you should know that increasing the width of the tape
shallow foundations make it possible to build heavier
houses with an attic. Large width of the foundation strip (and, accordingly, the base)
helps reduce the depth of soil freezing in the space under the floor.

What to consider when installing a shallow foundation

• Soil type

Shallow foundations are built on heaving soils
soils

It is prohibited to pour MZLF on biogenic organic soils,
for example, peat, sapropel (deposits of freshwater bodies), as well as on
clay. The photo shows that their appearance does not bode well.

Soil type

• Groundwater level

The closer the water is to the surface of the earth, the more unstable the MZLF will be

Shallow strip foundation - groundwater level table

Height difference

Related article: The sofa will fit perfectly into any interior

If the terrain is characterized by a significant difference
height (house on a slope), then the installation of a shallow strip foundation
it is quite problematic. In this case, the usual
strip foundation or a significant area under the MZLF is leveled. From the point
In terms of time and money, both options are equivalent.

• Laying depth

It represents the height from the lowest point of the foundation,
the so-called sole - to the zero mark (ground surface).

• Climate (depth of soil freezing)

Quite common among builders, bookmark
shallow strip foundation at a height calculated according to
formula – freezing depth minus 20%. So you can be sure that
the foundation will rise with the building.

Minimum depth of shallow strip foundation
regulated by SNiP II-B.1-62.

Depth of shallow strip foundation SNiP - table

Soil freezing depth for some Russian cities
is given in the table.

Soil freezing depth for Russian cities - table

You can also use the depth calculator
soil freezing.

How to calculate the load on a shallow shallow foundation

First of all, you should consider:

• design features of the structure;
• building height;
• planned number of floors;
• materials from which the walls will be built;
• coating weight;

Advice.
In general, the entire load can be divided into constant
(calculated before construction starts) and a variable. The latter depends on
number of inhabitants, weight of furniture, etc.

• trench depth;
• pillow thickness;
• foundation strip parameters;
• quality of concrete.

You can additionally use the foundation calculator

Calculation of a shallow strip foundation

1. Depth is determined by the proximity of groundwater and
freezing depth.

2. Height above the ground surface = 4x width.

Good to know. The height above the ground is less than or equal to the depth.

3. The width is determined by the formula:

Where, D is the width of the foundation base;
q – design load on the foundation, t/m;
R – design soil resistance, t/m2. This indicator
for a laying depth of 300 mm, is given in the table.

Formula pillow thickness4. The thickness of the cushion is determined based on the soil strength conditions of the area.

For highly heaving soils, the following formula is used:

Formula for highly heaving soils Where, tn is the thickness of the cushion;
A, C, W – coefficients;
A and C are determined from the tables below.
A W = 0.1 or 0.06 m2/t for heated and non-heated
heated structures.

Above the line - for MZLF with a laying depth of 300 mm, below the line
– for non-buried foundations.

Advice.
Calculate the MZLF using both formulas and give
preference for the larger value.

Cost of a shallow strip foundation

Varies between 4-6 thousand rubles. per linear meter. Price
depends on width, height, number of jumpers and dimensions, for example, cost
erecting the foundation of a 6x6 house will cost 70-80,000 rubles, and 10x10 =
120-150,000 rub.

Types of shallow strip foundation (shallow foundation)

Depending on the type of MZLF, its technology will differ
devices. Therefore, you should briefly familiarize yourself with the main ones:

Strip monolithic shallow foundation

Poured directly at the construction site, in
the result is a seamless tape

Strip block shallow foundation

Blocks are purchased ready-made or manufactured
separately, and are only assembled at the construction site. As fastening material
a cement solution is used.

Related article: Rustic kitchen - design, decoration, photo

Strip block shallow foundation - diagram

Each of them has its own advantages and disadvantages. But, in
In general, the service life of the second is three times less than that of the first. Therefore, in
In this article we will dwell in detail on such a type as monolithic MZLF.

MZLF technology or how to make a shallow-depth tape
DIY foundation

The instructions are easier to understand if all the work is divided into
clear steps. Let's not deviate from this scheme. So, the tape device
shallow foundation are as follows:

Preparatory stage

1. The place where it is planned to pour the foundation is cleared
from everything unnecessary.

Advice. Uproot trees that are nearby along with their roots.

2. All necessary material is delivered to the workplace and
tool. Moreover, it is advisable to immediately determine the location of all this
good, so as not to waste time searching for it later.

Marking for strip foundation

The importance of this stage is difficult to overestimate. Therefore it is necessary not
just “figure out” where you will dig a trench, but also make landmarks using
ropes (if possible, a laser level would be better).

How to make markings for the foundation:

1. take measurements around the perimeter;
2. put beacons in the corners;
3. check the diagonal between the corners;
4. if necessary, move the beacons;
5. make a blind area at a distance of at least a meter from the beacons;
6. attach a rope to the blind area boards, which will
   show the edges of the foundation.

The marking process is presented more clearly in the diagram.

Marking for strip foundation - diagram

How to dig a trench for a foundation

Foundation trenchA foundation trench is a strip of excavated soil.

The depth of the trench is determined by the depth of the shallow strip foundation and
pillows.

Foundation trench slope. For example, the most common depth is 300 mm; the thickness of the cushion is about 200 mm, depending on the quality of the soil. Then the depth of the trench will be 500 mm.

Advice.
To prevent the edges of the trench from crumbling, make small slopes.

Considering the type of soil, it is better to start pouring the foundation
immediately. Otherwise, it will crumble and some of the work will have to be repeated.

The sand cushion for the foundation is a mixture of sand and
crushed stones. You can mix them, but it’s easier to pour them in layers. Wet each layer
water and compact well. Since the structure of the pillow is quite
porous, it is separated from the main foundation with a waterproofing film.

In principle, the basis for a strip foundation
shallow-depth natural soil can serve, but its bearing capacity
much lower than the proposed sand and gravel bed.

Pillow for strip foundation

Formwork for strip foundation

Install the entire formwork structure vertically. Supports
fastened in increments of 500-600 mm. They are needed so that, under the weight of concrete, the formwork
did not fall apart or warp.

Formwork for strip foundations Useful advice.
Try to keep the boards adjacent to each other tightly and without sudden changes. Then you will avoid work on leveling the surface of the finished foundation for cladding.

Pouring strip foundation

Obtaining concrete is an individual matter - you can buy (or rather,
order) and the concrete will be delivered with a mixer or made independently, and
using a homemade concrete mixer (and the second option, how to make a concrete mixer from a washing machine).

For country house or individual construction, it is irrational to use a powerful deep strip foundation. The load from the building allows the use of shallow-depth type strip foundations. But which structure is considered a shallow support, and what are the requirements for it? It is necessary to consider this issue in detail.

For all types of strip foundations, including shallow foundations, the height depends on:

• depth of soil freezing (climatic conditions of the area);
• the presence of a basement in the house (the required level of its floor, the height of the base);
• groundwater level (GWL).

In the first case, it is important to ensure that the sole is located below the layer of freezing soil. In the case of a shallow foundation, special measures are taken against frost heaving of the soil. This measure is necessary to prevent movement of the base of the building due to the forces of frost heaving. If the house has a basement and the decision is made to use a shallow foundation, a sufficiently high base will be required that will provide the required height.

Groundwater is often located at a fairly large depth, so the main problems with it arise when designing a deep belt. For a small foundation, it is important that they are located 50 cm below the sole.

Restrictions on use

The use of shallow strip foundations is limited. It is not suitable for the following cases:

• on the building site there is a junction of layers with different characteristics (in the horizontal plane, that is, at different points of the site there are different soils near the surface);
• the groundwater level is closer than 1 m from the ground surface;
• the presence of layers of soil of organic origin (peat, silt, sapropel) within 1 meter from the surface of the earth;
• highly heaving soils (silty sand, bulk soil);
• buildings higher than two floors.

It is important to note that massive brick and concrete houses can only be erected on shallow T-shaped foundations. Rectangular tape is used for buildings made of foam concrete, timber, logs and frame houses. The problem with highly heaving soils is solved by replacing a layer with poor characteristics with sand of medium or coarse fraction. Groundwater, if it is located high, can be drained using a well-designed drainage system.

Determination of depth

Factors that influence the value have already been given earlier. Each is discussed separately below.

Soil freezing depth

The most important problem when supporting a shallow tape is the forces of frost heaving. They occur in the soil above the freezing mark, and for most of the country this mark is within 1.2-2.0 m. It is not possible to place a shallow foundation and fully comply with the requirements for the depth of support, so additional measures are required.

In general, the minimum depth of the tape can be taken from the table.

For most of the country, the value is 0.5 m. To prevent damage to foundation structures during alternate freezing and thawing of the soil, the following measures must be taken together:

1. Insulation. It is carried out in two stages. The first is the protection of the outer vertical surface of the tape. The insulation is attached along the entire height of the structure (underground and above-ground parts). The second stage of insulation is the installation of a warm blind area.
2. Sand cushion installation. To prevent frost heaving, a preparation with a thickness of 30-50 cm is arranged under the support. Sand of medium or coarse fraction is chosen as the material; fine sand will shrink during operation.

It is most effective to place horizontal thermal insulation at the level of the base of the foundation. Vertical thermal insulation must cover the entire foundation.

Foam plastic or extruded polystyrene foam (penoplex) can be used as insulation. They have very high thermal insulation characteristics and are resistant to biological influences, which is especially important in the current operating conditions. When pouring a monolithic strip foundation, permanent polystyrene foam formwork is also often used. Its use significantly simplifies formwork and thermal insulation work, reduces financial and labor costs for the construction of a shallow foundation.

Important! The exact value of the soil freezing mark can be found by determining the type of soil and using it, which presents a table of values ​​for large cities in Russia.

Depth of groundwater

To determine the presence of water in the ground, a site survey will be required. When building independently, it is carried out in two ways:

• cutting pits by hand;
• development of wells using a hand drill.

By analyzing the vertical walls of the pit or the soil on the drill blades, the type of soil, its physical properties, and water saturation are approximately determined. The strip foundation can be supported 50 or more centimeters above the groundwater horizon. If the soil is heavily saturated with water, it is better to think about supporting the house on screw piles.

You can also remove moisture from the strip base using a drainage device. To do this, drainage pipes are laid at the level of the base of the support to ensure the required slope.

The influence of depth and groundwater level can be combined in one table based on table. 5.3.

Soils on which the support occurs tape foundation	Depth sole laying
	if groundwater is located at a distance of less than 2 m from the freezing depth	if groundwater is located 2 or more meters below the freezing depth
Coarse and rocky rocks, gravelly sands, coarse and medium fractions	Does not depend on freezing, Accepted based on the minimum values ​​in the first table	Does not depend on freezing, is taken according to the minimum values ​​​​in the first table
Fine and dusty sands*	Depends, assumed to be no less than the freezing depth
Sandy loam
Clays, loams, coarse rocks with silty filler		Depends, at least half the freezing depth is assumed

Location of the basement or first floor floor level

If a decision is made to construct a basement or technical underground, the level of its floor should be 20-30 cm above the support level of the strip foundation. But it is important to remember that the buried part of the tape cannot be smaller than the above-ground part. This rule should be taken into account when choosing the height of the base. The same requirement applies to the ground floor floor if it is located close to or below the ground surface.

As a generalization, we can give the following minimum values ​​for various soils (without taking into account water saturation):

• clay - half the distance to the freezing mark;
• sandy loam, coarse rocks, sand (except for fine and dusty ones) - 0.5 m for most of the country, 0.75 for regions with a very harsh climate.

The correct choice of the mark for the base of the strip foundation, as well as taking measures against frost heaving (insulation, cushion, drainage) guarantee its stability and design load-bearing capacity.