Stepped foundation. Features of the construction of a strip foundation on a slope

Today with active suburban construction There are practically no unsuitable places for building a house. Houses are built on loose and marshy soils, as well as on very steep slopes. The only requirement in such work to ensure the reliability of the foundation under the building is compliance with the peculiarities of foundation construction for specific conditions.

If there is a need to build a foundation on a slope, the work must be approached with particular seriousness, since in such places there is always the possibility of a landslide after heavy rainfall or melting of deep snow as a result of sudden spring warming.

In order to successfully construct the foundation, the following work steps must be performed sequentially:

. selection of a high-quality foundation, taking into account all the features of the site;
. calculation of the foundation (ideally with the involvement of specialists);
. purchase of necessary quality materials;
. performance construction work.

Following construction procedures goes a long way in protecting the structure from foundation problems and resulting damage. In the case where the foundation for a house is being built on a slope, the quality of the materials used for it must be especially high.

Types of foundations on a slope

The construction of any house begins with choosing the type of foundation for it. The further safety of the building located on the slope depends on how correctly it is done. The first thing to note when talking about choosing a base is that slab foundation It is extremely rare to settle on a slope. It is practically unsuitable for construction on uneven surfaces.

The following types of bases should be selected from the bases used:

. pile foundation - the design is ideal for sloping terrain, as it allows the construction of a building without changing the terrain due to different depths of the piles. The pile foundation is the best solution during construction on a slope;
. shallow strip foundation - the foundation is reliable for light and medium-weight buildings, but its price is significantly higher than that of a pile or pile-screw foundation on a slope;
. stepped foundation - is one of the types strip foundation, this base is the most expensive of all.

In order to choose the best option for yourself, you should not only correctly assess the quality of the site, but also your financial capabilities. If the foundation is being built on a slope, its price can be a fifth of all construction costs.

For a house on a slope, the most reliable and easy-to-make foundation is a foundation made of piles. To make the work as easy as possible, screw piles should be used. In this case, the excavation stage is completely eliminated.

In order to build a foundation on a slope with your own hands, you should follow a certain sequence that will allow you to avoid mistakes. First, you need to mark the area and determine how much the piles should rise above the ground. The thing is that on the slope, the height of each row will change.

After the marking is completed, they proceed directly to the construction of the foundation on the slope. Installation of piles begins from the top. Then screw in the opposite lower support. This will make it easier to navigate when determining the height of the next piles. The height of all their tops must certainly be the same, otherwise the building will not have a reliable foundation.

After the piled part of the foundation on the slope is ready, they begin to arrange the monolithic foundation of the house or grillage. It depends on what device is provided by the project for a specific foundation on a slope. If it is decided to make a monolithic base, special slabs are used. The grillage is arranged in the same way as with a pile foundation on a flat surface.

For construction on a slope, it is possible to use a more expensive type of foundation - a stepped one. It is one of the types of strip base, specially designed for sloped areas. Its price compared to a screw one is much higher, like any tape type, due to the significant consumption of materials. Such a foundation on a slope is suitable for all buildings that can be erected on a strip foundation.

At the beginning of the construction of this type of foundation, a pit is dug on the slope. If the soil at the construction site is sandy, then to avoid crumbling, the slope should not be tilted more than forty degrees. If the soil is completely unreliable, the stepped foundation will have to be abandoned. The depth of the base is determined by the quality of the soil, and the width varies from thirty to eighty centimeters depending on the material used for the walls. The height of each step cannot be more than thirty centimeters.

You can make such a foundation on a slope in the same way as a strip foundation on a flat surface. The only difference is the fill. The foundation on a slope must be poured in stages, filling the formwork of each step with concrete separately, as independent foundation. In order to accurately imagine what the foundation on a slope should be like, it’s good to study the photo.

The foundation for a house must be of high quality and reliable, regardless of the soil on which construction is carried out. If you approach the construction of a building with all seriousness, then even on the most seemingly problematic site you can build an excellent house that will last for many years without the need for repairs. If a person does not have confidence in his abilities, then he should refuse independent construction and invite specialists.

Building a foundation on a slope for a house with your own hands is a difficult but feasible task. Before you begin, you need to correctly select the type of foundation for the house. Construction on an uneven foundation has its own characteristics and recommendations, which must be taken into account.

The number of difficulties depends on the location of the elevation difference. If the construction of a house at different levels is planned on the banks of a river or reservoir, complications associated with high humidity may arise. Violations of the stability of the foundation soil can be expressed as follows:

liquefaction of the base when moistened;
sliding of layers of soils with different characteristics relative to each other;
destruction of the slope base and splitting of the slope;
shedding of unstable soils along a slope with a large slope steepness.

The way out will be to choose the type of foundation correctly and strengthen the place of height difference with your own hands.

Strengthening slopes and banks of reservoirs

There are five effective options that can be used to prevent soil shedding and sliding.

If there is a problem with water flowing down a slope and destroying it, trays are provided at the place of the height difference that will direct the liquid along the desired path.

Advantages of building on a slope

Despite the complexity of the work, construction on a site with a difference in elevation has some advantages over construction on flat terrain:

protection from seasonal flooding with proper installation of a system of trays that drain water from the slope;
increased protection from the wind if the building is located on the southern slope of the mountain;
you can make a very beautiful landscape, but it will take a lot of time and money;
usually opens from the slopes good view to the area.

The second advantage is also a recommendation for choosing the location of the house on the site. If you make sure that the elevation is located on the northern facade, then heat losses will be reduced due to additional protection. This will lead to lower home heating costs in winter.

Pile foundation

It will be the least labor-intensive and reliable foundation for a slope. It is better to opt for metal screw piles. Suitable for steep slopes, sandy unstable and swampy water-saturated soils. The document regulating the calculation and construction of pile foundations is SP 24.13330.2011.

The advantages include:

reliability when building a house in difficult conditions;
low cost compared to other types of bases;
low labor costs during construction;
possibility of carrying out work at any time of the year;
Can be used for areas with elevation differences of up to 45 degrees.

The disadvantages include the impossibility of building a house with a basement. The piles are screwed in so that their heads are at the same level, and the ends buried in the ground are at different levels.

The foundation on a site with a slope using piles is erected in the following order:

select the length of the products, taking into account the steepness of the slope and a small margin;
mark the foundation of the house;
the piles are immersed in the ground by screwing, which makes it possible to make blades at the end of the products (the first pile is located at the top point of the site);
after installation, the piles are cut to the required length with a metal cutting tool;
pour concrete into pipes;
a grillage is installed, the formwork of which has not only vertical panels, but also a bottom.

Monolithic reinforced concrete, rolled metal (channels, I-beams) or timber are used as a grillage. If there is no need to construct a basement, it will be the most optimal option to ensure high reliability and low cost.

The second option for a pile foundation is. The supports are made from monolithic reinforced concrete. First, wells are drilled into which reinforcement cages are installed. After this, the piles are filled with concrete. The downside of the technology will be the need to wait time for the concrete to gain strength (28 days). Wells are developed so that the ends of the piles are in the same horizon. At the same time, the upper heads are also leveled. In fact, for each individual element, only the depth relative to the ground is calculated.

One of the options for a bored base could be a design using TISE technology. the foundation in this case looks like a nail with a head, pointing upward. The widening in the sole area increases the load-bearing capacity and prevents pulling out.

Columnar foundation

This option is suitable for light buildings when you need to make a foundation on a slope with a small difference in height. are not suitable for massive buildings, for this their load-bearing capacity is insufficient. There are also restrictions for soils with poor characteristics. Design and installation are carried out according to SP 25.13330.2012 and SP 50-101-2004.

The work is performed in the following order:

erect a retaining wall in the upper part of the site, which is a strip structure with a trapezoidal cross-section;
in the same way, a retaining wall is made in the lower part of the site;
soil is poured between the retaining strips with layer-by-layer compaction;
along the perimeter of the future house, holes are made, the geometric dimensions of which must correspond to the calculated dimensions of the pillars;
the foundation is made in pits, the edges of individual pillars must be carefully aligned in height;
make a grillage along the edge of the house foundation.

There are two ways to make a foundation on a slope with your own hands from free-standing structures:

from prefabricated concrete blocks;
made of monolithic reinforced concrete.

The second method is preferable because it avoids the need for lifting equipment.

Strip stepped foundation

Before you start work, you need to make a choice between different construction technologies:

monolithic reinforced concrete;
prefabricated reinforced concrete.

For the same reason as in the previous version, the monolithic method is the most optimal. In addition, the foundation built using this technology is a solid product. When constructing this type of foundation, they are guided by the joint venture “Design and construction of foundations and foundations of buildings and structures.”

You can make a support for a house with a slope of 10% in the following order:

The slope on which the tape will rest is cut so that a stepped descent is formed. The height and width of the ledges are calculated so that the angle between the horizon line and the visual line drawn from the surface of the ledge to the base of the slope does not exceed 30 degrees.
The steps of a kind of terrace are compacted and reinforced with reinforcing mesh.
A layer of soil is poured over the mesh.
Dig trenches under retaining walls located across the slope, formwork is installed and the foundation is poured. Walls located along the slope are placed in such a way that their edges are at the same level, while the mark of the sole may differ.
After the concrete has hardened, soil is added in order to equalize the difference between the lower and upper elevations of the slope.

If the slope percentage of the site is less than 8%, a stepped slope is not necessary. The strip foundation is installed as for a flat area. It is important to note that tape is one of the most disadvantageous types when working with height differences. Construction at different levels will be very labor-intensive and expensive. It should be used only if a basement is needed.

Slab base

Also suitable for a house with a basement. with preliminary development of the soil. The structure is inserted into the slope, before which it will be necessary to level the base under the slab.

Important! Any type of foundation cannot rest on an inclined surface. The sole should always be level or staggered.

The advantages of the plates include:

ease of filling;
stability when working on heaving and subsiding soils;
high load-bearing capacity.

But compared to piles, a slab is an expensive proposition.

To summarize everything, we can say that the most preferred type of foundation for a slope is screw piles. But they are suitable only if you plan to make a relatively light house without a basement. If the future owner decides that a basement, plinth or technical underground is necessary, he will have to opt for a more expensive foundation option. When constructing any type of foundation, it is recommended to familiarize yourself with SP 25.13330.2012 and SP 50-101-2004.

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Unanimously.

Tape is the most reliable and economical base design option, tested in all conditions by many years of practice.

All technological issues have been worked out to the point of complete clarity; errors can only occur when constructing a belt without a proper survey of the site, using unreliable data or untrained builders.

Let's consider one of the most difficult, but often encountered cases - the creation of a strip foundation on a slope.

Such situations occur quite often, so the issue deserves detailed consideration.

Strip foundation is one of the most preferred options. It is optimally adapted to receive and redistribute loads arising from movement or heaving of the soil.

All alternative options foundations when building on a slope create significant restrictions in the design of the house, for example, in parts. In addition, the presence of a slope can become an obstacle to the approach of construction equipment, which will make installation of piles impossible.

At the same time, you can dig a trench yourself; the main condition will be to ensure that its bottom is horizontal. This is the only truly important and difficult moment when creating a tape on a slope; all other stages are performed in an almost traditional way.

NOTE!

It must be taken into account that we're talking about about small slope angles, where there is no danger of soil runoff during spring or autumn intensification of hydrogeological activity. These issues should be clarified in advance with surveyors and geologists.

Advantages and disadvantages

The advantages include:

Strength, ability to withstand multidirectional loads.
High load-bearing capacity, resistance to external factors.
Opportunity self-construction without the participation of complex technology.
Cost-effective, relatively low consumption of building materials.

There are also disadvantages:

Dependence on the structure of soil layers.
The loads are directed at an angle to the axes of the tape, which must be taken into account when calculating the foundation.
A thorough examination of the site is necessary to determine the level of occurrence groundwater and composition of layers.

There are many contraindications due to hydrogeological or climatic conditions, which must be fully clarified before starting work.

What types are suitable for the slope

Possible construction different types tapes.

By design can be selected:

By depth of immersion:

Experts recommend building monolithic structures, since the load-bearing capacity and resistance to axial tensile loads of prefabricated belts is much lower. Considering the specifics of the placement and the possibility of soil movement under the influence of the weight of the building, the choice is completely justified and obvious.

There is also a general consensus regarding the depth of the tape. It is recommended to prefer the recessed type, since heaving loads in winter time directed at an angle and capable of moving the base down the slope.

The greater the angle of inclination, the greater the immersion depth should be.

What is a stepped strip foundation?

When constructing foundations of a large area on slopes with a sufficiently large angle of inclination, it is recommended to use a stepped strip foundation. It is usually used in cases where the difference in levels at the lower and upper points exceeds 1 m.

From a design point of view, a stepped strip foundation is a kind of terraces, horizontal platforms located one below the other.

This division facilitates construction in terms of excavation work, since it is much easier to ensure horizontal alignment on a small site than on a large area - the volume of soil that will have to be removed for leveling is reduced several times.

When creating steps, you can reduce their size until a completely acceptable height difference is obtained for each section, but you cannot reduce the size too much, as this reduces the adhesion strength of the foundation to the ground.

Slope specifics

It is necessary to understand that mathematically flat and horizontal sections do not exist in principle. If the slope is within 3% (for each meter of length the difference is no more than 3 cm), then the site is considered to be horizontal.

If the percentage of the slope is greater, then there is a certain slope. If at the lowest point the height of the base is 4 times the width of the tape, the slope value is considered the maximum. For large values, it is impossible to build a continuous strip; a stepwise construction method must be used.

The stepped base also has its limitations. For example, the length of the horizontal section of the tape (step) should not be less than 0.6 m, and the height of the tape should not be less than 0.3 m.

In addition, each step located on the next tier must overlap the lower one by double the width of the tape or by 0.3 m (minimum).

What is its structure

With a relatively small angle of inclination, the construction method differs little from the generally accepted one. The only peculiarity is the need to ensure a horizontal level of the bottom of the trench under the tape.

During construction on developed slopes, where it is necessary to use a stepped tape, several adjacent tape bases appear, located above each other and resting with their lower parts on the upper sections of the steps located underneath them.

This configuration requires a certain construction order, which is carried out from the bottom up and allows the steps to be built sequentially. In this case, one-time filling of the entire tape is not always possible, so it is necessary to ensure only the solidity of individual steps.

How to calculate the foundation

A full calculation of a tape located on a slope should be carried out by an experienced and professional specialist. The task is too complicated even for a professional if he has not performed such calculations before.

It is necessary to take into account the angle of inclination, hydrogeological factors, and other features of the site and climate in the region. In this case, even numerous online calculators will not help, since the combination of influencing factors in each case is very specific and an average calculation method is not enough.

If the slope is small and cannot affect the performance of the belt, produced in the usual way. In this case, the issue is resolved by conventional planning or leveling of the site.

Step-by-step installation instructions

Procedure for constructing a strip foundation on a slope:

Marking the area, installing stakes in the corners of the future trench.
Digging a trench to the depth required by geological conditions.
Leveling the bottom of the trench horizontally.
Creating a layer of sand backfill. As an option - alternately a layer of sand and crushed stone.
Careful compaction of sand.
Checking the horizontal surface of the sand layer. If necessary, correction and alignment are made.
Laying a waterproofing layer.
Formwork assembly.
Installation of reinforcement frame.
Curing of the concrete tape, during which the tape is periodically wetted with water for 10 days.
Stripping (carried out 10 days after pouring).
After curing for 28 days, the surface of the tape is covered with a layer of waterproofing and insulated. After this, further construction work begins.

The construction of the stepped belt is carried out in stages, starting from the bottom step. For each of them it is necessary to carry out a full cycle of work to create all the elements of the foundation. Some points can be combined, for example, excavation work or installation of insulation.

NOTE!

Each case of construction on slopes is unique in its own way, so only a specific project with a complete list of construction conditions can be considered in more detail.

Useful video

In this video you will learn how to properly install a strip foundation on a slope:

Conclusion

The terrain rarely allows you to do without site planning. Construction on slopes is not uncommon, so knowledge of methods and technologies for solving such issues is useful not only for professional builders, but also for people planning to build a private house on a site with difficult terrain.

In any case, the participation of a specialist will be useful at any stage of the work, and especially at the stage of creating the project. Therefore, when starting work, you should attract a competent and knowledgeable foreman who has experience in creating support structures on an inclined plane.

In contact with

A stepped foundation is a foundation with several steps in height, which is arranged to expand the base. The foundation must be built, observing all the rules, only then will it become reliable foundation building. This type of foundation is used when construction is planned on an area with uneven terrain.

Location of stepped foundation

When building a house on an area with complex terrain, you must proceed from the direction of its slope. This important point, as it plays a decisive role in the stability of the foundation of the house. On soft soil or a slope, the house must be positioned with its long side perpendicular to the slope. In this way, maximum resistance to soil pressure can be created.

Stepped foundation pit

In order for the foundation to be strong and stable, it is necessary to dig a pit under it. A safe slope angle in the pit does not lead to sliding or crumbling of the soil. For clay soils, a safe angle is considered to be 50-60 degrees, for sandy soils – no more than 45 degrees.

In the construction of stepped foundations, the pit is not dug along the entire perimeter of the building at once, but gradually, one step at a time. This is due to the fact that each step requires support in the form of continental soil.

First, the soil is removed along the foundation line on the slope and above the laying level. In this case, the angle of inclination must be observed. If the soil lies in places, then it is better to remove this soil to a depth when the mail becomes dense. In this case, the trench will be narrow and its depth will not be very great. If the house according to the project has a basement, then the pit must be made wide. The part of the trench that remains under the strip-type foundation is dug only by hand. It is better to start digging from the bottom point of the foundation marking, gradually moving up the slope. In this case, it is necessary to measure the length and height of each step. The width of the pit should be larger than the foundation.

Stepped foundation formwork

To prevent the earth from crumbling, it is necessary to lay a special formwork near the ledge. The formwork must be continuous. To do this, its vertical parts are installed on the ledges. Typically, such formwork is not removed after concreting so as not to destroy the structure.

Drainage of stepped foundation

The stepped foundation requires deep foundation in some places. It is in such places that it is worth making wall drainage, which is done according to a separate project.

When building a house on an uneven slope, the hydrological conditions change, so drainage can be called necessary step in the construction of a building. If this is not done, water will flow down the foundation walls, which will lead to the formation of a water stream under the building. As a result, the soil will begin to sag and deform the building. Drainage pipes They collect this water and take it outside the house.

Reinforcement of a stepped foundation

The stepped foundation always has a slope and follows the slope of the terrain as much as possible. Therefore, for such a foundation it is necessary to select a certain height of the ledge. When laying a concrete foundation, the ledge cannot be more than 30 centimeters.

Each stage of the foundation must be additionally reinforced if construction is carried out on weak and heterogeneous soil.

If the foundation steps must be more than 60 centimeters in height, then they are made of reinforced concrete and additionally reinforced with transverse horizontal rods. When the angle of inclination of the terrain of the site and the foundation is more than 18 degrees, and the ledge is more than 30 cm, it can be made strong and reliable using additional reinforcement with anchors.

Waterproofing a stepped foundation

On a stepped foundation, waterproofing is laid in the same way as on flat foundations. Sheets of roofing felt are laid overlapping: the top strip should always overlap the bottom strip by 10 centimeters.

Stepped foundation walls

Step foundation walls are built in exactly the same way as traditional foundation walls. They can be built from monolithic concrete, and also make masonry from brick or rubble stone. If the height of the foundation ledge does not coincide with the foundation blocks, they can be trimmed or additionally added with something small.

Very often, buildings can be erected in areas with unsettled terrain: mountainous areas, hills, ravines. In such cases, you have to carefully study the geology of the site in order to select a reliable and stable foundation. A strip foundation on a slope is not particularly complicated; if the construction technology is followed, it can be erected with your own hands in problem areas.

Foundation on a slope: varieties

The foundation for a building on a site with a slope must meet the following requirements:

Ensure the stability, strength, reliability and durability of the building.
Have protection against possible landslides.
Resist the harmful effects of groundwater and flood waters, if such a danger exists at the development site.

A strip foundation on a slope is the key to the stability of the structure

For the construction of reinforced foundations, the following types of foundations are most suitable:

Strip foundation (direct configuration) is a classic version of the supporting foundation for a building, which is distinguished by greater reinforcement of structural units and elements. The construction of this type of foundation on a slope will entail significant material and labor costs.
Strip stepped foundation - performed depending on the topography of the site in three options, each of which has its own pros and cons. We will talk in more detail about the technology for making stepped supports for a building below.
Columnar foundation - constructed from individual pillars installed in pre-prepared pits. Individual pillars are buried to the level of stable soil, so the support can be considered reliable. A base frame is installed between the pillars, which carries the load like a retaining wall.
Pile field made of screw piles - for a house or bathhouse on a slope. A pile foundation made from screw supports is easily installed by hand, and the screwed piles can be extended to considerable lengths. This option for a pile foundation is not suitable for houses with deep basements.

Technology for constructing a stepped foundation

In areas with a slope and complex terrain, buildings are located taking into account the direction of the slope, without taking into account the location of the cardinal points and ensuring the best natural lighting.

In this situation, the priority is to ensure the stability and stability of the supporting base.

Digging a pit on a site with a slope is quite difficult; it is very important to choose the correct slope angle.

When performing excavation work to prepare a pit, it is necessary to prevent the occurrence of soil shedding and sliding.

The following standards are usually accepted:

Sandy soils – from 30 to 45°.
Clays, loams - from 50 to 60°.
Freezing soils - 70°.

A special feature of preparing a pit for a stepped foundation is the need to build each individual step of the foundation with support on continental soil, so a sufficiently large volume of soil is removed so that the formation of steps does not cause certain difficulties.

Excavation and formwork installation

Foundation on a slope

Excavation work begins by digging a pit for the foundation by removing the top part of the soil in an area with a slope. When carrying out work, be sure to observe the angle of inclination; the soil is removed above the level of the supporting foundation.

When building a house with a basement, you will have to dig a pit for the foundation. For a house without a basement, it is sufficient to prepare separate narrow trenches corresponding in size to the individual steps.

It is most convenient to start excavation work from the lowest mark, moving up the slope.

It is very important to provide a trench for the construction of steps slightly wider than the base of the foundation.

The height and length of individual steps are measured in accordance with the design drawings. The formwork is installed immediately during the preparation of the steps, thus avoiding soil shedding on the ledges. Installed panels are rarely removed after the foundation is poured; usually the formwork is designed to be permanent.

The prepared trenches are leveled at the bottom, compacting the soil at the bottom. The installed formwork is lined with a layer of protective waterproofing. Formwork for a stepped foundation, its production and installation are quite labor-intensive and complex process, because often the foundation is located at great depth, which requires additional work to install reliable drainage.

To construct a foundation on a slope, the formwork is made from wooden materials, it is important to ensure that the shields do not have significant gaps.

Reinforcing the foundation for a house on a slope

For a house on a slope this is a very important job that requires attention. When providing a concrete ledge, it is very important to remember that its height should not exceed 0.3 m.

Reinforcement of a strip foundation is carried out using a spatial reinforcement frame, connected (or welded) from reinforcement with a diameter of 10-20 mm. The formwork must be higher than the reinforcement frame installed in it, so that during concreting, reinforcing bars do not remain on the surface of the poured foundation.

Reinforced step reinforcement is provided for moving or weak soil. In rare cases, it is possible to use steps with a height of more than 0.3 m.

In this case, reinforced concrete products with additional reinforcement with longitudinal and transverse reinforcing bars are used. If necessary, the ledge is strengthened with anchors; this is done if there is a significant slope of the surface on the site (more than 18 degrees).

Concreting and foundation care

The concrete mixture for pouring the foundation will have to be prepared at the construction site, because it is quite difficult for heavy concrete trucks to drive to a site with difficult terrain. It is advisable to pour the foundation structure in one day to prevent the formation of dried layers of concrete mixture.

When laying concrete in formwork, the mixture should be compacted to avoid the occurrence of voids inside the structure. Typically, such “pockets” are formed at the intersections of the reinforcement cage. The formwork must be filled with concrete to the proper marks, the surface of the mixture must be carefully leveled.

A monolithic concrete structure will gain strength for up to 28 days, during which time the formwork should not be disturbed. It is allowed to remove the panels from the foundation base after 2 weeks, when the structure gains up to 70% of the design strength. Permanent formwork must remain in the body of the foundation supports.

After the stepped support structures have gained strength, you can begin building the walls.