Monolithic slab on the ground on a strip foundation. Installation of a floor slab in a strip foundation

Date: 01/15/2015
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Principles of foundation construction on the ground

The foundation is a structural part of a structure, its base or support, which transfers its load to the ground. It can be located not only in the ground, but also above the surface of the earth and in water, although this is very rare. Therefore, it will not be entirely correct to consider the foundation underground part building.

Ideally, the support of a structure should be strong, stable and viable, that is, adapted to various changes not only in the external environment, but also in the soil. Therefore, maximum attention should be paid to the underground part of the foundation.

Calculations when designing the support of a building must be as accurate as possible, otherwise the entire construction will end with the formation of cracks in the walls of the house, disruption of masonry joints, etc. All work on the construction of building supports is carried out below the “zero mark”, indicating the floor level on the first floor.

The level of quality of construction may not be determined immediately, but after some time.

To prevent the foundation from slanting, during its construction it is necessary to make it level, otherwise the house will not last long.

The site chosen for construction may have weak soil for the foundation or high ground groundwater. This causes uneven settlement of the soil. Therefore, the construction site must be thoroughly examined. All this will allow you to make the right choice of foundation type when designing on heaving soils. There are 3 types of deformations of the building support:

Sedimentary – soil displacement under the influence of groundwater movement and climatic conditions.
Temperature – changes in the dimensions of a building structure due to temperature changes.
Shrinkage – changes that occur as a result of loss of moisture from the base material of the house.

In order not to carry out unnecessary excavation work in order to lay a deeper foundation, one should not skimp on geotechnical work. Too great a depth can lead to deformation of the entire building and its destruction. All this will take up extra time. The terms that characterize the foundation are:

The sole, that is, the horizontal plane, is the lower surface of the support structure.
Laying depth is the distance from the base to the surface of the earth.
The edge is the boundary between the above-ground structure and the foundation.
The sole and edge have length and width, the vertical distance between them is equal to the height of the structure.
Vertical planes are lateral surfaces, which can be external or internal.
The soil has several layers, the topmost of which is called load-bearing, and all the rest are underlying.
Waterproofing is a structural layer of waterproof materials, which can be vertical or horizontal.
The base is the part of the foundation that is located above the ground, since the entire structure cannot be underground. The foundation should rise above ground level by about 30 cm or more.
The pick-up is an element that is used instead of a base in.
Foundation deformation.

Having familiarized yourself with the basic concepts, you can move on to, which is not limited to constructing a pit and performing work on the construction of walls. At the very beginning, preparatory work should be done.

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Carrying out preparatory work on foundation construction

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Selecting the required type of foundation

Foundation strengthening scheme.

Before finally choosing a site for construction, it is necessary to draw up a plan and determine the purpose of the future building. It is necessary to determine whether there are underground communications in the selected area. The construction of a building within the city requires that the walls of the house do not extend beyond the red line, as this will be considered illegal. Especially where architectural monuments are located and appropriate development regulations apply. During the operation of the building, it is very important that the result of the construction of the house is a rigid structure. The foundation of a house with such characteristics will allow you to evenly redistribute all local deformations and any loads from the soil.

For light houses made of timber, a shallow foundation is usually laid. For heavy buildings with several floors, built of brick or foam concrete, a buried foundation is laid on heaving soils, which is advisable.

It will depend on the depth at which the groundwater lies. At a low level, any type of foundation can be laid: pile, slab, strip. A shallow foundation on heaving soils is installed when water cannot be drained using a drainage system if the water level is high.

For example, a strip foundation cannot be laid on deeply frozen soils that are subject to severe heaving. This type of foundation is used very rarely on these types of soil. The process of conducting engineering-geological analysis before the site should include the following main points:

Determination of the degree of soil freezing.
Estimation of the load from the building on the foundation.
Identification of soil type.
Setting the service life of the building.
Determination of level.
Study of the possibility of installing a drainage system.
Preparation necessary materials for construction.

It will depend on its quality, which is determined by a responsible and competent approach in the process of choosing the type of foundation. To avoid unexpected expenses, all the nuances must be thought through at the design stage.

As a result of the design and survey work carried out, the most suitable suitable look foundation: slab, columnar, strip or pile. Columnar or strip foundations are suitable for individual construction of low-rise buildings.

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How to analyze soil heaving?

At the first stage of building a foundation on the ground, an analysis of its heaving is carried out. The peculiarity of the analysis is the assessment of soil at depth. This assessment makes it possible to design the foundation taking into account the susceptibility of the soil to frost heaving, which occurs as a result of the transformation of accumulated liquid into ice.

First, a well is developed to select soil at different depths, and the degree of heaving of the soil is determined. This indicator is associated with the increase in soil during its freezing to a depth of 1 m. If the level of the indicator is more than 0.01, then the soil is heaving, that is, increasing by 1 cm or more at a depth of 1 m.

The degree of soil heaving is equal to the ratio of the change in its volume in absolute terms to the height level of the soil before it freezes. After the analysis has been carried out, they begin marking the soil surface for the foundation. Let's take a closer look at the stages of analysis:

Selection of soil while drilling a well to form a water source. In this case, the depth of the well should be 50-70 cm greater than the freezing depth level. This will allow for the most accurate assessment of heaving.
If the soil is heaving, then it should include clayey soil types, that is, loam, sandy loam and clay containing many pores in which moisture accumulates. The amount of clay and water in the soil determines its heaving. The more there are, the higher the estimated indicator.
Since the soil contains soil and fill layers that are not suitable for laying a foundation on them, these are first removed. Only the clay layer of soil, which has a high bearing capacity, is left.
In the process of designing a foundation, one should take into account how uniformly the soil will swell over the entire area of the foundation. As support for the foundation of the house, those layers of soil that have a low level of heaving are chosen.
It should be taken into account that in the summer, when the ground freezes, the building along with the foundation will lower, and in the winter, when the ground freezes, it will rise. Medium-porous and large-porous layers, which lie lower than the freezing level, are more suitable support.
If the soil is heaving, then it can be replaced with compacted sand and gravel before, having previously moistened the layers. The groundwater level is also noted before laying the foundation of the building. If they are located high, then they should.
After analyzing heaving, it is necessary to take basic and additional measures to ensure that the foundation being constructed is durable.

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Measures taken against soil heaving and foundation deformation

If special measures are not taken to reduce and prevent soil heaving, then at a certain point the structure may be lifted by heaving forces. The following measures are taken against heaving of the soil under the foundation:

They dig a pit, removing from it a layer of soil that is subject to swelling, which is replaced with coarse or gravelly sand. The new layer is then compacted well. On sandy soil, which has increased load-bearing capacity, it is possible to carry out work on constructing any type of foundation. This method is associated with a higher level of costs.
You can ensure the stability of the foundation on the ground by laying it at a lower level than the freezing depth. in this case will not be subject to heaving forces, which will affect only its lateral surface.
In order to reduce the influence of heaving forces, you can use a layer of insulation laid on a layer of soil. This is the most suitable method for light buildings and shallow foundations. The thickness of the insulation depends on the construction site.
Heaving can be eliminated if you arrange drainage system at the construction site, allowing for water drainage. The depth of the specially dug ditch and the foundation must have the same dimensions. A perforated pipe placed in a filter fabric is placed in a ditch with a slight slope.
The pipe in the ditch is covered with gravel or coarse sand. Water flowing from the ground will be drained through a pipe into a drainage well with a hole.
To ensure natural drainage of water for this purpose, it is necessary to prepare a sufficiently low area. For this purpose, a blind area and storm drainage system are installed.

A feature of heaving soil is its uneven freezing and thawing. The integrity of the underground foundation structure is compromised by uneven deformations coming from the base. This is due to the fact that in winter the soil under the foundation on the north side will freeze faster and take longer to thaw in summer, and vice versa in relation to the south side.

Thus, it is recommended to always make a rigid one that will be capable of redistributing local or local loads with maximum efficiency. Therefore, in the process of building a house it is impossible to do without reinforcement of the foundation.

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Features of the work on laying a foundation on the ground

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How to lay a strip foundation correctly with your own hands?

After the soil analysis has been carried out, it is necessary to make markings for the base of the strip foundation and begin its arrangement. When constructing low-rise buildings, the width of the strip foundation can be about 40 cm. The markings are done both internally and externally.

First, you should draw a perimeter according to the dimensions provided in the foundation design. Then hammer them into the corners of the perimeter with pegs through which to pull a fishing line or string. For internal markings, the necessary indentation is made, which is equal to the width of the strip foundation.

Strip foundations, as the most common supporting structure, due to the simplicity of its implementation and low cost, are highly reliable. If you have some knowledge in the field of construction strip foundations, then this structure can be built in just 1 month.

A shallow strip foundation must be laid to a depth of 40 cm. To do this, it is necessary to dig a trench, the base of which must have a flat surface, and the soil in it must be thoroughly compacted. After this, a layer of gravel or crushed stone is laid in the trench.

To install a strip foundation, it is necessary to prepare the following materials and tools:

Concrete.
Fasteners
Concrete mixer.
Insulation.
Notched trowel.
Floor slabs.
Fittings.
Boards for formwork.
Crushed stone.

If you plan to prepare the concrete solution manually, then in this case a concrete mixer is not used. Before starting work, you will need to prepare the following materials:

Sand (sifted).
Clay (softened).
The water is cold).
Lime (quicklime, ground).
Cement.

The necessary tools will be the following:

Sifting sieve (2x2 mesh).
Container made of wood or metal.
Trowel.

The proportions of pulp from clay and sand for the purpose of preparing 1 batch, the volume of which will be determined by the size of the container for preparing the solution, are taken as follows, that is, 1 part of clay:

to 2 parts sand;
to 3 parts sand;
to 5 parts sand if the clay pulp has a high fat content.

To prepare the mortar, purified sand and clay are used so that after laying and drying the mortar, shrinkage does not occur and cracks do not appear on the foundation walls.

Concrete preparation for the installation of a strip foundation is carried out subject to the following rules:

A thin type of concrete with a size of 5-10 cm is used. The strength of concrete can reach 50% depending on weather conditions. The foundation is made a week after pouring the concrete, when it has already accumulated required level strength.
Concrete preparation is carried out on the basis of low-quality lean concrete B7, which allows obtaining a smooth and even surface. After this, the foundation is waterproofed. When the groundwater level is low, anti-capillary waterproofing of the foundation is used. Concrete preparation in this case is replaced by the use of a membrane.
The use of a profiled membrane allows you to create more reliable conditions for concrete hardening. The membrane will prevent the “cement milk” used when pouring concrete from flowing into the soil layer. The surface of the membrane is studded, which creates additional friction at the base and can prevent the formation of cracks in the foundation.

If concrete preparation is replaced by using a membrane, then the construction period of the foundation will be reduced, the material costs related to the purchase of reinforcement and concrete. In this case, there is no need to lay the foundation after the concrete has completely hardened, that is, after a week.

The quality of concrete pouring will depend on the selected brand of concrete and the correct calculation of all loads in the process of designing foundations on heaving soils. The composition and grade of concrete will depend on weather conditions. For favorable normal weather conditions, the M200 concrete grade is suitable. Higher grades are suitable not only for warm, but also for cold weather.

During the construction of a strip foundation, special substances can be added to the concrete mixture, the content of which can be equal to 1-2%. They have increased plasticization and frost resistance. In this case, the concrete hardening process will be accelerated. To lay a reliable structure, a reinforcement frame and formwork are used.

The reinforcement frame is knitted from reinforcing bars using a crochet hook and special wire. In some cases, specially treated reinforcement is connected using welding machine. Before constructing the frame, formwork is installed, and the frame is knitted directly into it.

When the reinforcement frame is ready, they begin pouring concrete. The mixture should consist of 1 part cement, 5 parts crushed stone and 3 parts sand. All components should be thoroughly mixed and filled with water. When pouring, the formwork may lose stability, so it is supported with special planks. After pouring, it is necessary to remove voids using a reinforcement rod that is poked into the concrete pour.

Strip foundations have become popular for the construction of low-rise buildings due to their simple technology and low cost of work. It is a closed loop made of reinforced concrete, which is located along the perimeter of the load-bearing walls.

But if you decide to make a concrete floor in your house, you will be faced with a choice of how to arrange it: pour a concrete floor on the ground or make strip foundation slabs into self-supporting structures.

Panel ceilings

To save money on internal backfill, many people use prestressed slabs with round voids for floors. This is the best option in terms of price/quality ratio, but if you place them on a strip foundation and tightly seal the space inside, then over time moisture from the soil will accumulate there.

Therefore, it is necessary to provide through ventilation in this case. To do this, the foundation must protrude above the ground to a height of 40-50 centimeters, so that in winter the snow does not cover the ventilation openings.

The photo shows an example of floors after 6 years, made using this technology without ventilation. As you can see, at the junction with the foundation, rust from the reinforcement is visible, since this is the most vulnerable part of the slab.

It is worth considering that most often the base is at a much lower height, and you will not be able to make ventilation holes, or they will be closed in winter.

Floor on the ground

If the house does not have a basement planned, then a more reliable, but expensive option would be to make a floor on the ground. Roughly speaking, a monolithic slab will be poured inside the foundation. In this case, the floor in the house will be durable and it will be possible to install heating.

It is important to ensure that the strip foundation or slab is not rigidly connected to each other. Otherwise, over time, one of the bases will shrink, cracks and height differences will appear.

Can be implemented using the following technology:

and sprinkled outside and inside to the same level.

Note!
The internal backfilling of soil must be done in layers of 20-30 cm.
Only this thickness will allow the layer to be well compacted using a 100-150 kg tamper.

To compact the soil, you need to apply a layer of crushed stone on top of it with a fraction of 40-60 mm. If there is a high load in the room, then you need to use fine crushed stone with a fraction of 10-20 mm. It is imperative that you then walk over it with a tamper so that the bottom layer of crushed stone goes into the ground.

The next layer will be concrete preparation. It is needed as a basis for hydro-vapor barrier. If you place it directly on crushed stone, then during work the builders will damage its tightness.
The vapor barrier must be laid with an overlap on the walls. If this layer is not made, moisture from the soil will enter the finished floor structure and condense there.
Next it is laid. Extruded polystyrene foam is well suited for this due to its low water absorption, high durability and compressive strength.

Advice!
To protect against the penetration of cold from the ends, you need to fix the insulation with an overlap on the walls.
It will serve as a damper for the screed.

The floor screed is made with reinforcement with welding mesh 100*100 with a section of 3 mm. If the screed is made in a highly loaded room, for example in a garage, then the mesh should be 50*50 with a section of 4 mm, and the screed thickness should be at least 10 cm.
The last step will be the finishing of the floor. It can be any material: tiles, porcelain stoneware, laminate, linoleum, etc.

To better understand this technology, we recommend watching the video in this article.

Is it possible to save money?

Such a strip foundation with a slab inside will be expensive, but by following this technology, you will provide your home with high durability and reliability.

How can you save on construction?

First of all, you can replace the vapor barrier with ordinary polyethylene film. But you definitely need to lay it in two layers. However, it is worth considering that polyethylene is a fairly delicate material and can be easily damaged during construction work.

If your layer of internal backfill is less than 20 centimeters, you can compact the soil with clay. This way you will be less likely to tear the film on crushed stone during installation.

Note!
It is worth considering that polyethylene will not provide a good vapor barrier, and moisture will still penetrate inside.

Popular mistakes

The most common mistake is violating the order of the slab cake or using other materials. Many people simply do not understand the purpose of each layer.

For example, if you first lay a layer of geotextile, and then a layer of crushed stone, such a layer will be of no use. Geotextiles will not allow the soil to be well compacted with crushed stone due to its density, and it will not provide vapor and waterproofing.

Also, in this case, expanded clay cannot be used as a filler to increase the level. It has high water absorption, and when you pour it with a concrete screed, it will absorb moisture and the concrete will take much longer to dry. For the same reason, it cannot be used as insulation. There are much more effective materials that do not absorb moisture.

Conclusion

Thus, you can make a reliable concrete floor in your home with your own hands, which will rest on the ground. For this, a low foundation of 20-30 cm above the ground will be sufficient. This is especially true if ready-made low FL strip foundation slabs are used.

And if you lay floors directly on the ground, you cannot avoid negative consequences. The floor must be raised above the ground. Since the early 60s of the twentieth century, houses in which the floor was laid directly on the ground were common. Due to this, moisture, bad odors and mold began to appear in many homes.

In the 90s of the twentieth century, principles were developed according to which it was recommended to build houses:

- build houses only on soils suitable for this purpose

Before you begin to eliminate shortcomings and shortcomings, you need to identify their cause. Here are some tips:

— Insufficient cut-off of capillary moisture is very difficult to eliminate. This occurs because the insulation material is inaccessible because it is located under the slab. It is necessary to lay the drainage pipes deeper and see how well they function.

— The next method of protection is as follows: you need to remove all the floor covering, then lay synthetic material with an air gap on the concrete. Then re-lay the flooring, either removed or new. Thus, penetrating moisture is removed through the air gap. Ventilation of the baseboards also needs to be ensured; this can be done using gaskets.

— An excellent flooring material is clinker tiles, as they allow moisture to pass through from below.

— If possible, install underfloor heating

— Improve ventilation in the house

A monolithic foundation slab is the most reliable and solid foundation that can support buildings of enormous mass. Such a foundation evenly distributes the weight of the overlying structure over the entire area of the soil. It is also called “floating” for its ability to level out ground movements.

The monolithic slab foundation can be ribbed or flat. A ribbed slab has a higher resistance to soil heaving and building loads, but such foundations are difficult to construct. First, you need to fill in the ribs, on top of which the monolithic slab itself is cast. The gap between the ribs is filled with sand or sand-gravel backfill.

Regular stove

A conventional monolithic reinforced slab with a thickness of 200 mm is usually laid flush with the ground on a sand cushion also 200 mm high. However, there are several types of conventional slabs, for example, with crushed stone and foam complex, with waterproofing, geotextiles and polystyrene foam. The last two options are different big amount necessary layers. In the case of polystyrene, first, as usual, sand preparation is made on the ground, geotextiles are spread over it, on which a layer of crushed stone and concrete preparation are laid. Waterproofing is spread on the concrete, on which the insulation - extruded polystyrene foam - is laid. It is protected with a layer of plastic film and now the monolithic slab itself is being cast directly into the foundation.

Soils for foundation monolithic slab

The monolithic slab foundation is suitable for heaving soils, sandstones, and areas with high groundwater levels. Such a foundation will withstand even seismic instability. On highly heaving soils, a monolithic slab foundation seems to be one of the best options for cottage development, including buildings with increased sensitivity to uneven deformations. It is better to erect such structures on shallow or shallow reinforced concrete monoliths on cushions made of non-heaving materials. Houses that are overly sensitive to deformation include buildings with walls made of brick, aerated concrete, expanded clay concrete and other similar materials. Violation of the integrity of such walls occurs even with small deformations of 1-5 mm.

In the Moscow region, areas with weak heaving soils and high groundwater levels include Pushkino, Shatura, Orekhovo-Zuevo, Noginsk. Here it is better to build a monolithic slab foundation that does not allow settlement.

For what types of buildings is a monolithic slab foundation suitable?

The monolithic slab foundation will support even the heaviest structures made of brick, stone and reinforced concrete, not to mention large wooden country mansions with several floors or frame buildings. Multi-storey buildings are built on monolithic slabs residential complexes and skyscrapers. Most of the ancient churches and temples, including those in Russia, have stood on the monolith for centuries. Slab foundations are widely used in industrial construction, in the construction of shopping malls and sports facilities, and in road construction.

Monolithic slab foundation: pros and cons

The main advantages of a monolithic slab are the highest strength, reliability during sudden temperature changes, movement of soil layers, and the absence of the need to lower it below the freezing depth of the soil, which significantly reduces construction costs. The foundation can be used as the floor of the first floor. One of the undoubted advantages of a monolith is its versatility - a monolithic slab foundation is suitable for any structure and any type of soil. Despite enough high cost building materials and work, the safety margin of the monolithic base will allow you to painlessly change the project upward at any time or use old foundation for the construction of a new big house, without strengthening the existing foundation.

A monolithic foundation slab also has its disadvantages. This type of foundation is one of the most expensive, as it requires a large consumption of concrete and reinforcement. The construction of such a foundation is quite labor-intensive, taking about 1-2 weeks. It is also not recommended to erect structures on such a foundation on slopes, only if a monolithic foundation slab is erected on piles, and such a foundation is the most expensive and labor-intensive.

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