What Type Of Foundation To Choose

Table of contents:

What Type Of Foundation To Choose
What Type Of Foundation To Choose

Video: What Type Of Foundation To Choose

Video: What Type Of Foundation To Choose
Video: How To: Choose A Foundation | Sephora 2024, March
Anonim
  • The nature of the building / foundation / foundation interaction

    • Soils and their features
    • Building features
    • Ground water
    • How the foundation works
  • Foundation design issues
  • Basic types of foundations

    • Column foundation
    • Strip foundation
    • Slab (solid, floating) foundation
    • Pile foundation
  • How to drain the site
  • Strip foundation. Part 1: types, soils, design, cost
  • Strip foundation. Part 2: preparation, marking, earthworks, formwork, reinforcement
  • Strip foundation. Part 3: concreting, final operations
  • Strip foundation. Part 4: assembling concrete block structures
  • Column foundation
  • Pile foundation
  • Slab foundation
How to choose the type of foundation
How to choose the type of foundation

This article begins a cycle devoted to the construction of the foundation for a private house. In our next publications, we will talk about the nuances of building specific types of foundations.

The construction of the foundation is considered one of the most difficult and responsible tasks in the construction of a home. Not surprisingly, not every would-be homeowner would dare to take on this job on their own. Despite the difficulties, laying the foundation is probably the most exciting phase during which the life of a new home begins. This is because the foundation is the true foundation of the building, its backbone and soul. One has only to start - and there is no turning back.

What are the difficulties, why are there so many special requirements for foundations? Simply, it's not only about the use of high-quality materials and adherence to technologies, which, however, is also difficult to overestimate, practice shows that the greatest number of "punctures" occurs due to errors in calculations, or, even worse, construction without design, "like a neighbor's." … These problems often have catastrophic consequences, up to serious deformations of the supporting structures, and most importantly, they are detected already during operation and are practically not amenable to correction.

How to choose the type of foundation
How to choose the type of foundation

Another scourge of the domestic developer is a frank desire to save money. The customer purchases materials of dubious quality, hires inexpensive low-skilled workers, consciously calculates the loads acting on the foundation and foundation, "at a minimum." The cost of a foundation for a low-rise building, depending on many factors, can reach 25% of the total estimate, and is rarely less than 5–8%. Many people come across this, because it is a pity to bury such money in the ground.

On the other hand, an overestimation of possible loads is a direct path to a significant rise in the cost of construction, both due to overconsumption of materials and an increase in labor costs. Sometimes an unnecessarily deep foundation works to the detriment (on heaving soils).

The nature of the building / foundation / foundation interaction

The choice of a specific type of foundation, materials, method of its construction depends on many interrelated factors. The most important thing in making decisions is to take into account that the building and the natural foundation on which it stands interact in a certain way with each other, and the foundation is an intermediate link in a single, very important chain. These elements have a physical and even chemical effect on each other; certain forces begin to act between them, which we will talk about below. Therefore, they need to be considered only in unity.

Soils and their features

The building with its weight through the foundation presses on the foundation, compresses it, as a result of which powerful stresses arise. The issues of determining the bearing capacity of the soil (including in the horizontal direction) and its resistance to deformations are becoming relevant. A weak foundation can not withstand the loads and provoke settlement, subsidence, rise, horizontal shear, roll, deflection, bending, twisting, vibrations of the foundation - all this can cause serious deformations.

The most important aspect of the foundation / soil interaction is the friction and adhesion forces that arise between them.

In the case of an unsatisfactory condition of the soil, which cannot serve as a reliable foundation, it is fixed (compaction, silicatization, cementation, bituminization). Anchoring the foundations is a complex technological task that only specialized organizations can implement. This type of work requires the creation of a separate soil consolidation project.

How to choose the type of foundation
How to choose the type of foundation

The construction characteristics of the soil are directly influenced by its composition; on this basis, several types of bases are distinguished:

  • rocky (granite, limestone, quartzite - no heaving, practically no groundwater, excellent bearing capacity);
  • coarse-grained (crushed stone, pebbles, grit, gravel - very reliable, not heaving, uniform sediment);
  • sandy (more than 50% is sand with a fraction of less than 2 mm - a good base with a uniform bedding, not heaving);
  • clayey (clay particles more than 30% - they easily pass water, have heaving);
  • loam and sandy loam (clay, dust, sand mixed with each other - moderately strong, heaving);
  • specific soils with special properties (subsidence, swelling, saline, organic, eluvial, bulk, alluvial).

To select a foundation, soils are separately divided into heaving and non-heaving. Heavily foundations are easy to pass and retain water. In winter, they are saturated with moisture, freeze and increase in volume - by about 15%. The soil expands, rises (and unevenly) and pushes the foundation up. During thawing, the soil settles along with the building. Such seasonal shifts cause serious stress on the foundation. The heaving of soils directly depends on their density, dispersion, and groundwater level. Soils of this type include silty and fine sands, clayey soils, coarse-grained with clay filling. The most unfavorable in this regard are clay bases. The problem of frost heaving is solved by using columnar or shallow foundations with increased rigidity of the aboveground part,at least there is a delusion "the deeper the foundation is laid, the more reliable."

Building features

Depending on what kind of load the structures put on the base, they are conventionally divided into light and heavy. If the heaving forces exceed the weight of the building, this is a lightweight structure, and it is usually built on a shallow foundation. But a house whose weight exceeds the total tangential heaving forces is considered heavy. To redistribute this mass, a large deep-lying foundation is being erected.

The weight of the structure and, accordingly, the choice of the foundation is mainly influenced by the material of the walls. Obviously, wooden buildings will be light - frame, log, from a bar. Quite different foundations will be needed for heavy brick, block, concrete, multi-storey buildings with load-bearing slab floors - usually they are made of reinforced concrete, tape or pile type.

How to choose the type of foundation
How to choose the type of foundation

It should be said that a certain imprint on the choice of the type of foundation (more even on its configuration) is exerted by the constructive type of building, which determines the spatial arrangement of the main load-bearing elements - walls, floors, supporting columns … For example, for frame houses and buildings with massive load-bearing walls, foundations are used various.

In some cases, the nature of the operation of the building may be taken into account, for example, it will be heated or cold.

It is very important whether there will be buried rooms in the house, which will need to be carefully protected from groundwater.

Ground water

This is the third force, or rather, one of the most important factors of the “foundation / foundation” interaction. The water balance of the site directly affects the choice of the foundation design, the method of its construction, the depth, and dimensions. Water, being in a suspended, free and capillary state, constantly moves in the base under the influence of gravity, pressure difference, surface tension. With a high level of ground, underground and man-made waters (as well as with a sharp change), the base becomes waterlogged and loses its bearing capacity, there is a danger of soil swelling and subsidence, and the forces of frost heaving increase.

How to choose the type of foundation
How to choose the type of foundation

The hydrogeological conditions of the territories, their possible changes during construction and operation are always taken into account. Here the seasonal and long-term amplitude of fluctuations in the water level, the possibility of the appearance of "top water", the height of the capillary rise of moisture are important. According to this criterion, the site is defined as:

  • non-flooding;
  • potentially flooded (requires special measures: drainage of the territory and foundation, water-lowering wells, anti-seepage curtains, electroosmosis, special waterproofing);
  • drained (there is a likelihood of soil settling with a sharp significant decrease in the level of groundwater - relevant for clay and organic, silty bases).

The chemical composition of ground and industrial waters is considered separately, since they can be very aggressive towards the foundation materials. In this case, measures are taken to protect the foundation from corrosion - a special type of waterproofing.

How the foundation works

The foundation connects the box from below, acts as a kind of belt for load-bearing walls, does not allow them to "disperse", restraining internal stresses (for example, even pile and columnar foundation structures are connected by beams or slabs).

How to choose the type of foundation
How to choose the type of foundation

It takes the full load from the building, redistributes its mass. This structural element is the lowest, it experiences the greatest pressure, because the whole building acts on it, which, upon completion of construction, will have a certain integrity. This means that the foundation must tame the loads, which often act unevenly, due to which not only compressive, but also tensile and shear forces arise that act from above.

The foundation transfers the weight of the building to the foundation. Simply put, the building with the help of the foundation clings to the ground and retains its design position. Various harmful forces can counteract here: lateral shearing, overturning, sliding, pushing out … It is interesting that the foundation does not always rest on a sufficiently solid stable foundation, more often the friction force in dense layers does the main work, which is why it is so difficult to build on loose and moving soils.

Some types of foundations are more effective than others in protecting the interior of the house from groundwater (for example, monolithic tape). This statement is relevant especially when they are high, or if the project provides for a basement, basement, underground garage.

How to choose the type of foundation
How to choose the type of foundation

Some intermediate conclusions can be drawn.

The foundation must be:

  • strong enough to withstand and efficiently distribute loads;
  • resistant to shearing, pushing, overturning forces;
  • durable, have a service life no less than the house itself;
  • neutral to groundwater;
  • economically feasible and least time consuming in construction.

It is wrong to say “what foundation is needed for this house?”, It is correct to say “what foundation to build on these soils (the house will be such and such)?”.

Foundation design issues

If we are talking about a small garden house, assembled from what is at hand, then you can independently calculate the foundation. But if you build something more serious, for example, from brick (especially attic houses, two or three floors), then perhaps you cannot do without the involvement of specially trained people. The cost of the services of an engineer will pay off a hundredfold, especially since he is responsible for his work and without fail signs the project. Having a competent project on hand and having certain construction experience, you can already start building the foundation yourself, or invite contractors and control the process according to the documentation received.

How to choose the type of foundation
How to choose the type of foundation

Foundation design is carried out for all stages of its construction - transportation and storage of elements, direct installation, operation. The development is carried out on the basis of the technical assignment from the customer (this is the data that we must provide to the designer). So, what information is needed to accurately select and calculate the foundation?

First, detailed characteristics of the future building will be required. What is needed is, in fact, a detailed project containing:

  • information about the dimensions, configuration and materials of structures;
  • data on space-planning decisions;
  • information about loads transferred to the foundation.

Particular attention is paid to the presence and nature of underground premises: basements, garages, basement.

How to choose the type of foundation
How to choose the type of foundation

Second, a site plan is provided with reference to the terrain, elevation marks, indicating the relative location of all possible buildings. It is desirable that a network of paths and sites, a scheme for laying buried communications have been developed and indicated in advance. It will not be superfluous to decide on landscape works and the nature of landscaping, since these moments significantly affect the water balance of the territory.

Thirdly, it is imperative to carry out engineering-geological and hydrological exploration at the site (this work can only be trusted by licensed organizations). These surveys will determine the bearing capacity, resistance of the foundation, and other features. There will be data on the relief and positioning of the site; seismic conditions; type and physical and mechanical properties of soils, their stratal location; the presence and level of groundwater, their balance and fluctuation regime, the chemical composition of water (aggressiveness towards building structures); observation of unfavorable geological processes - side work, landslides, karsts, temperature anomalies; freezing depth. Geological exploration is recommended to be carried out not only in the built-up area, but also near the site.

Fourth, we indicate the class of responsibility of this structure, which determines the requirements for maximum deformations. In our case, this will be the "normal" level of responsibility (second class), which is accepted for mass housing construction.

Fifth, in the case of a lack of information, or a particular complexity of conditions, in-situ measurements and monitoring are used.

How to choose the type of foundation
How to choose the type of foundation

The developer makes a number of very important decisions and displays them in the corresponding drawings and explanations. He must:

  • depending on the type of building, determine the actual load on the ground and the stresses arising in the base of the foundation;
  • calculate the stability of the building;
  • justify the use of a specific type of foundation;
  • determine the possibility of using a natural foundation, or justify the organization of an artificial foundation;
  • to develop in detail the structure of the foundation, possibly several options (zero mark, axes, sections of nodes and pits, specifications, reinforcement schemes, formwork characteristics, drawings of finished reinforced concrete products);
  • choose a material (concrete grade, section and reinforcement, the nature of the pillows …);
  • calculate the depth of all foundation elements;
  • choose / offer the most profitable and least labor-intensive construction method.

In addition to the drawings, the project is accompanied by a list of regulatory documents according to which the project was developed, as well as an explanatory note on the initial data (research) and analytical justifications of the decisions made by the developer. By the way, SNiP 2.02.01–83 is the basis for calculating the foundation, although more than two dozen related manuals are used.

Basic types of foundations

There are many types of foundations, and, as a rule, several designs may be suitable for one house. Let's try to figure out how different foundations differ from each other, in what conditions they can be preferable, what are their disadvantages and advantages.

Taking into account the structure of the building (for example, the presence of a basement), hydrogeological conditions (heaving of the base, high groundwater), the nature of the loads (mass of the building), a certain depth of foundation is chosen. By the depth of location in the soils, the foundations are conditionally divided into:

  • shallow
  • buried
How to choose the type of foundation
How to choose the type of foundation

A shallow foundation is, as a rule, a strip monolithic structure, which is laid above the freezing depth (50–70 cm from the level of the site). This type of foundation is used only for relatively light low-rise buildings (including brick with hollow-core slab ceilings), which do not exert heavy loads on the base. Shallow structures cannot be used for buildings with basements and basements. But they are less labor-intensive, more than twice as economical as buried ones, and are great for building on heaving soils.

The deepened foundation can be either monolithic or prefabricated, which falls below the freezing depth (more than one meter). It is considered the most durable and can withstand the very heavy loads produced by heavy stone houses. This option is indispensable if the building design assumes the presence of recessed rooms. A monolithic buried foundation can become an effective barrier to the penetration of high groundwater into the interior of the house. The disadvantage of this design is its high cost and labor intensity; a deep-seated foundation is not suitable for heaving soils.

According to the manufacturing method, foundations are:

  • prefabricated
  • monolithic

The monolithic foundation is made of concrete / rubble concrete directly at the construction site. Thanks to this, it is possible to obtain various configurations and sections of the structure. A monolithic reinforced structure is capable of withstanding greater loads than a prefabricated one, only it can be used with an unfavorable water balance on the site. A clear disadvantage of this type of foundation is the need for strict adherence to concreting technology, careful maintenance of concrete. A monolithic foundation is more time consuming and takes longer to build.

How to choose the type of foundation
How to choose the type of foundation

Prefabricated foundations are built from piece elements, including stone, brick, but most often these are concrete / reinforced concrete FBS blocks of various configurations. Such a foundation is the most industrial one, since its main elements are manufactured in the factory. The assembly of the prefabricated foundation from the blocks is carried out with the help of technology, there is no need to assemble the formwork - due to which labor costs are significantly reduced, and this stage does not take much time. In addition, wet processes are minimized and a lot of work can be carried out even in cold weather. Precast foundation is not used on water-saturated soils, as moisture can penetrate into the gaps between its elements.

The construction of foundations is the most important factor that determines their purpose and main differences. On this basis, the foundations are combined into several separate groups:

  • columnar
  • tape
  • slab
  • pile

Column foundation

As the name implies, this foundation consists of recessed pillars, which are located at the corners of the building, at the intersection of walls, under the columns, in straight lines with an interval of 1–2.5 m. They are made of all basic foundation materials: stone, concrete, bricks and even wood. In turn, the load from the building is transferred to the posts by means of foundation beams.

How to choose the type of foundation
How to choose the type of foundation

This foundation is being built for light houses without recessed rooms, mainly wooden (walls made of log-houses, timber, frame, panel). Naturally, it will not work for stone buildings. It is also undesirable to use this foundation on soils with the likelihood of lateral movements (say, on large slopes), since, due to the small adhesion area, it will not be able to stabilize the house. The small support area does not allow the use of a columnar foundation on bases with a weak bearing capacity.

The obvious advantages of columnar foundations can be considered their simplicity and efficiency (approximately 2 times cheaper than strip foundations). This is the most profitable foundation in terms of labor costs. In addition, it is most effective in areas with a large freezing depth and on heaving soils.

Strip foundation

This popular and versatile type of foundation is erected under all the supporting structures of a building - main walls, a number of supporting columns. It is a continuous tape, it is a kind of walls in the ground, which can be prefabricated and monolithic, buried and shallow.

Strip foundations are used for heavy (brick, block, monolithic) houses with massive slabs that exert great pressure on the ground, but they are also suitable for wooden houses on any soil. It is economically feasible to use tape structures for timber houses built on very unstable foundations. Only this type of foundation is erected if there are basements in the building.

How to choose the type of foundation
How to choose the type of foundation

In most cases, the strip foundations are irreplaceable, but certain disadvantages of strip foundations can be considered:

  • labor intensity (a large number of earthworks, a large amount of concrete or installation work - for prefabricated structures);
  • high cost (many materials, almost always there is a need to use lifting equipment);
  • large dead weight (it increases the load on the base, which is taken into account in the calculations).

Slab (solid, floating) foundation

This type of foundations is a solid or lattice monolithic reinforced concrete slab, which is located under the entire building. It is the most reliable and successfully used for the construction of all types of buildings on all problematic soils (heaving, mobile, highly compressible, subsiding, loose sand cushions).

How to choose the type of foundation
How to choose the type of foundation

Reinforced solid foundation effectively redistributes the load from the house, it has excellent spatial rigidity and, thanks to the large supporting area, stabilizes the structure well. Slab foundations are best suited for protection against high groundwater, especially pressure. Due to the monolithic construction method, this foundation is easily erected under a building of any shape.

The inevitable disadvantages of a slab foundation can be considered:

  • high cost (a lot of concrete, a lot of reinforcement, but at the same time the slab is already a rough floor);
  • labor intensity (relatively large amount of work).

Pile foundation

This type of foundations consists of special long pillars (piles) with a pointed end, which are covered with a slab or beams (grillages). Piles can be made of wood, concrete, steel, with a combination of these materials - they are driven in, or screwed into the ground. Separately, there are rammed piles, which are made directly on the site, in a monolithic way in drilled wells. Piles can be an element of both solid and strip foundations.

How to choose the type of foundation
How to choose the type of foundation

In private construction, the pile foundation is rarely used, but sometimes it is very difficult to replace it with another structure. It is used if you have to build on very weak, heaving, swampy soils that are not able to withstand the heavy load of buildings, including for multi-storey ones. Piles can pass through unstable and water-saturated upper layers and transfer the load to a more solid foundation, and in some cases, "hanging piles" are used, which, by compacting the soil, hold the structure due to friction forces.

It should be noted that the pile foundation is quite economical (the cost is commensurate with the price of a buried strip foundation) and the least labor-intensive, since in most cases concrete is almost not needed, the volume of earthworks is minimized, and many operations are mechanized.

How to choose the type of foundation
How to choose the type of foundation

The only drawback of the pile foundation is the need to use special equipment and highly qualified specialists. You cannot do without the involvement of specialized organizations.

In the following articles, we will consider in more detail all types of foundations, we will pay special attention to the technology of their construction. And now I would like to once again emphasize the need for competent design of the foundation, during which the developer receives a technical and economic justification for choosing a particular type of structure. Remember, you cannot save on the foundation, the cost of mistakes is very high here.

Recommended: