The construction of houses on heaving soil itself is quite common in Russian regions, which are mostly cold and damp. Such construction always has a number of features that should definitely be taken into account. Let's take a closer look at these features.
What is heaving soil?
Heaving soil can be understood as any soil that has a heaving function. Heaving is a process , in which moisture in the soil, which has turned into ice, expands due to the lower density of ice relative to water and, accordingly, increases the volume of the entire soil.
It turns out that such soil seems to swell. Hence the name of this process. Obviously, heaving is characteristic of all soils, but it will manifest itself to varying degrees.
The main principles here are as follows. Firstly, the more water in the soil, the stronger the possible heaving. Secondly, the more soil is able to retain moisture inside itself, the greater its heaving.
Types of soils most susceptible to heaving.
Despite the fact that, strictly speaking, absolutely any soil is prone to heaving to one degree or another, in construction it is customary to identify a number of soils that are most susceptible to heaving.
Such soils include mainly all soils containing clay particles in their composition. Moreover, the more clay there is in the soil, the more susceptible it is to heaving.
Conventionally, the following are considered non-heaving soils: rocky clastic rocks, coarse-grained sands without admixtures of clay particles, medium-grained sand, gravelly sands. Fine sands containing large quantities of clay can easily be classified as heaving.
Why is heaving soil dangerous for a building?
When frost sets in, the water in the ground under and next to the foundation turns into ice. The density of the soil generally decreases, and the volume increases. Accordingly, the soil under and next to the building begins to swell.
The forces of frost heaving that will act on the building in this case can be divided into two types. Firstly, forces acting vertically from bottom to top, towards the surface of the earth. Such forces are capable of lifting the entire building or part of it.
Secondly, tangential heaving forces that act on the side surface of the foundation. Such forces are capable of turning and moving a building.
In the spring, when a thaw sets in and the ice turns back into water, the reverse process occurs - the density of the soil under the building increases, the volume decreases, and the building, accordingly, is lost. Movements of the building can lead to deformations, cracks and even destruction of the entire building.
Approaches to solving the problem of heaving.
There are several key moments for solving heaving problems.
Factors contributing to the reduction of soil heaving are as follows:
1. Elimination (removal) of clay from sand: clay is capable of holding water in the soil.
2. Coarsening of sand: water stagnation does not occur in such soil; Without stopping, the water quickly goes into the layers of soil below.
3. Heaving is possible only within the depth to which the soil freezes under the building.
4. Under a year-round heated building, the ground temperature is always higher and the depth to which the soil will freeze in the area of the foundation of such a building will be minimal.
5. If the groundwater is low enough, then the likelihood of heaving is reduced, since the first aquifer will be below the depth to which the soil freezes.
Methods for solving the problem of heaving.
Currently, there are many well-proven methods for solving construction problems on heaving soil that have proven themselves in construction practice. Let's list and analyze them.
1. Complete replacement heaving soil non-heaving soil.
This method, as the name implies, requires a large amount of land work for its implementation. The heaving soil in the area allocated for construction is completely removed and non-heaving soil, mainly coarse or medium-grained sand, is placed in its place.
This method completely solves the problem of heaving, since in such soil the water will not stagnate and will immediately go into the underlying layers of the soil, while, of course, the depth at which the groundwater lies is quite large - greater than the depth to which the soil freezes in winter period.
2. Soil drainage.
The method can be performed either independently or in combination with other methods. The essence comes down to draining the soil located under and in the area of the foundation of the building.
To do this, a trench is dug along the entire perimeter of the building, into which perforated (containing holes on their surfaces) drainage pipes are laid, connected to each other into a single drainage system.
The pipes are wrapped in geotextiles and sprinkled with pebbles or crushed stone on all sides. This is necessary so that only water from the soil flows into such a pipe, and the soil itself does not penetrate into it.
A drainage well is dug at a short distance from such a pipeline system, which is then connected to the pipeline system. The function of a well is to collect water from the drainage system.
In order for water to flow from the ground into the well by gravity, the pipes are laid with a certain slope, that is, the pipes furthest from the well are located slightly higher than the pipes that are directly adjacent to the well.
You can easily make such a slope if you backfill the trench before laying drainage pipes in it. at different levels crushed stone: near the well with a minimum layer, and at the most distant points of the drainage system with a maximum layer.
The depth of laying drainage pipes depends on the depth at which the base of the foundation is located and on the depth of groundwater in the area and is usually approximately 0.5 m.
3. Selecting an appropriate foundation for heaving soil.
A lot depends on the competent choice of one type of foundation or another. On heaving soils the most acceptable may be pile and monolithic. Let's look at them in more detail.
Construction idea pile foundation consists in the fact that the pile is buried below the depth to which the soil under the building is capable of freezing and, thus, will not be subject to vertical frost heaving - the most dangerous for the building.
A typical pile foundation using industrial, factory piles requires the use of a pile driving machine for construction and is considered expensive and difficult to construct.
Therefore, it has become widespread in low-rise cottage construction. a budget option- pile-screw foundation, based on screw piles that are screwed into the ground without the use of a pile driving machine or other complex equipment.
Another option is to use a slab monolithic foundation. This foundation is considered expensive in terms of costs. Its essence is that a monolithic structure is built on a pre-prepared sand cushion. slab foundation, on the basis of which the building is then built.
Thus, the foundation will be located above the level to which the soil under the building freezes and such a foundation will be subject to heaving, however monolithic foundation is a rigid reinforced concrete structure capable of rising and falling during heaving without any deformation or destruction.
A slab foundation requires numerous earthworks, as well as a large amount of concrete mixture, however, it is considered good protection against the negative effects of heaving soil.
4. Construction of a blind area and storm drainage system.
Storm drainage allows you to collect water that falls in the form of precipitation into certain containers and, thereby, protects the soil adjacent directly to the building from waterlogging. The blind area serves the same purpose, diverting water to a certain distance from the building.
A blind area is constructed around the perimeter of the building, usually using concrete or other similar building material that does not allow water to pass through. The width of the blind area must be at least 1 meter and it must have a slight slope in the direction opposite to the side of the wall (basement, foundation) of the building to which such a blind area is adjacent.
5. Weighting of the building.
Obviously, the greater the mass of the building per unit of soil surface, the less likely the process of lifting or shifting of the building during heaving becomes.
This is where this method follows: if the design allows, then the mass of the building is deliberately increased, including as a means of combating heaving.
6. Insulation of the foundation.
The idea of the method is to raise the temperature of the soil adjacent directly to the building above negative values. Thus, the soil located in the area of the foundation does not freeze and heaving does not occur. This is also facilitated by constant heating of the basement and the house as a whole in winter.
The choice of one method or another should primarily be based on the building design, soil geology and climate at the construction site. The fact of spending effort, time and money on implementing a particular method is also important. All this should be foreseen at the building design stage, before construction begins.
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Water in the ground is a dangerous phenomenon for the foundation. You need to start fighting it at the stage of designing a house. First of all, it is worth conducting geological studies that will determine the level of moisture location. Which foundation is suitable for high groundwater levels depends on a certain elevation.
Geological surveys in private construction are carried out manually. To do this, dig holes 50 cm deep below the expected foundation level or use the manual drilling method to the same depth. It is important that there is no accumulation of moisture at a distance of half a meter from the base of the building. Tests are recommended to be carried out in the spring (when the water level is highest) in the lowlands of the site.
With high groundwater levels, the foundation becomes a structure that is constantly exposed to negative influences. Moisture in the soil leads to the phenomenon of frost heaving - an increase in soil volume under the outer walls of a building. In this case, the central part of the house remains in the same position. Uneven deformations are the main cause of cracks in walls.
Freezing will also become a problem for the foundation material. Most often the structure is made of concrete. Moisture enters the pores of the underground part of the building and freezes there. When water freezes, it increases in size. This property distinguishes it from any other substance on the planet. At the same time, the pressure inside the concrete structure increases. In the spring, the structure thaws - the pressure decreases. This constant loosening of internal bonds in concrete leads to its destruction.
Groundwater on site can cause corrosion of materials if it contains alkalis or acids. This phenomenon is especially dangerous for concrete. When pouring, the reinforcement is protected by a layer of concrete 2-3 cm thick, which prevents damage.
Location of the groundwater level at a distance of 3 m or more from the surface
This situation is the most favorable. In this scenario, it is possible to construct buildings with a basement without any special measures. A recessed strip foundation is used as a supporting part. When clayey soils (clay, loam, sandy loam) occur on the site, it is necessary to take a number of measures to prevent frost heaving in the event of a possible rise in moisture in the spring and during heavy rainfall:
- resting the sole below the freezing depth (determined separately for each locality);
- vertical waterproofing of basement walls with bitumen or lining materials (roofing felt, linochrome, waterproofing);
- adding sand (medium or coarse fraction), crushed stone or gravel 30-50 cm thick under the base of the foundation;
- drainage device at the sole level.
Location of the groundwater level at a distance of 1.5 m or more
It is recommended to use a non-buried strip or slab as a foundation for high groundwater levels. Tape base Suitable for construction on solid soils. For fragile soils, a slab option is used. For small buildings it is allowed to use poles. The depth of the supporting part of the house is set in the range of 70-100 cm.
When constructing a shallow strip foundation on clay soils, it is necessary to provide protection against frost heaving. To achieve this, a set of measures is used:
- laying drainage at the base level around the perimeter of the house;
- backfill made of non-heaving materials (sand, crushed stone, gravel);
- insulation of the outer surface of the tape and insulated blind area.
If it is necessary to construct a basement and a buried foundation, it is necessary to provide reliable waterproofing. To keep the room dry, the following measures are provided:
- external waterproofing (for example, roll material using a protective screen);
- internal waterproofing (plaster, penetrating);
- use of concrete with low moisture permeability (not lower than W8) for pouring basement walls.
Also, a mandatory measure will be a drainage system around the perimeter of the building and a storm sewer to drain rain and melt water.
Location of groundwater level at a distance of 0.5 m or more
In this case, building a basement is a very expensive undertaking. It is highly recommended that you avoid it. When the water horizon lies at a distance of 0.5 m from the surface, non-buried types of foundations are used:
- columnar;
- tape;
- slab
The first option is practically not used due to low load-bearing capacity. The non-buried tape is only suitable for small outbuildings made of lightweight materials. This includes wood and frame structures. It is better to use a T-shaped foundation section (with a widening at the bottom), since it has a greater load-bearing capacity compared to a rectangular one.
If you need to build a large house, choose a slab. Its thickness and reinforcement are assigned depending on the number of storeys of the building and the material from which the walls are made (wood, lightweight concrete, brick). In this case, you will have to take care of insulating the structure, since the foundation is not protected in any way from the destructive effects of cold. A good solution would be an insulated Swedish plate (USP), for the protection of which extruded polystyrene foam or ordinary polystyrene is used. Penoplex is more expensive than polystyrene foam, but it will also provide waterproofing of the structure.
The technology assumes the presence of three ways to lay thermal insulation simultaneously:
- under the stove;
- vertical along the perimeter of the slab;
- insulated blind area.
To prevent frost heaving and increase the bearing capacity of the foundation, replace the soil. To do this, use medium or coarse sand, gravel or crushed stone. You can mix materials (sand and gravel mixture). On average, the thickness of the cushion is set to 30-50 cm. But if the soil on the site is weak, then the cushion is laid until it stops sinking into the ground and displaces excess moisture.
The location of the groundwater level is closer than 0.5 m
In this situation, the use of non-buried foundations is impossible, since the condition is not met: the groundwater level should be located 50 cm below the foundation support. The only solution will be piles. They differ in manufacturing technology, immersion method and material.
The most commonly used are reinforced concrete and metal piles. The most popular option has become screw elements made of steel. They allow you to carry out work even in very swampy areas without additional measures. This type of foundation is considered inexpensive and least labor-intensive, but it is applicable only for frame or wooden house: metal piles do not have high load-bearing capacity. The most common diameter of screw piles is 108 mm. The pitch and depth are selected depending on the load.
Reinforced concrete elements in private construction are made using the bored method. One of the subtypes of such piles are elements using TISE technology. They are especially useful in preventing frost heaving, as they have a widening at the bottom and prevent pulling out.
The bored type of foundation is suitable for buildings made of any materials. The main disadvantage is the complexity of manufacturing. Such a foundation with a high groundwater level requires temporary water reduction during the construction period, which significantly increases financial and labor costs.
To connect individual supports into a single structure, a grillage is installed along the edge of the piles. He can be:
- wooden (wooden or frame house);
- reinforced concrete;
- metal.
The last two options are mainly used in the construction of brick and concrete buildings.
A foundation with a high groundwater level is one of the most complex and critical structures.
Such a foundation for a house must be built taking into account many different factors, each of which must meet all the requirements associated with the danger of flooding and premature destruction of the building.
Accordingly, it is important to correctly determine the level of soil freezing, select the most suitable foundation design and ensure the presence of an effective drainage system.
Determining groundwater levels and possible concerns
Ground water level
The construction of the foundation at a high groundwater level must be stable and reliable. The extent of the threat of subsidence and destruction of the building is determined long before the start of construction work. For this purpose, in spring or autumn (at a time when the amount of moisture contained in the soil reaches maximum level) in the place where the basement will be built in accordance with the construction plan, you should dig a hole at least 3 m deep.
Dig a hole at least 3 m deep
To obtain accurate data, you will need to reliably protect the pit from weather precipitation. After a few weeks, a certain amount of water will appear and settle at the bottom. Perhaps the bottom will remain dry, and then the foundation does not require additional protection.
If the water is located at a distance above 2 m from the surface, it is necessary not only to calculate the depth at which the foundation will be built, but also to choose the right design.
What should the foundation be like in case of high groundwater, experts can say after conducting geological surveys.
Piles will raise the level of the house to a safe height
Among the existing foundation structures on high-level groundwater, pile structures are especially popular and trusted by consumers.
Their arrangement will help ensure high-quality and reliable protection of the foundation of the house from the negative influence of groundwater:
- flooding of basements;
- destruction of concrete structures;
- the occurrence and development of fungus and mold;
- violation of the integrity of the foundation itself when freezing during the cold season.
At high groundwater levels, the walls of the pit may float
In addition, high groundwater level causes the walls of the pit to melt and a sharp reduction in the bearing capacity of the soil. This will require execution additional work on the arrangement of an effective drainage system, including wells and catch basins.
The most dangerous process is the leaching of minerals from the soil, which significantly worsens the strength characteristics of the soil and leads to a change in its structure. Installing a foundation in such conditions has a number of limitations. Calculation of the depth at which it will be filled supporting structure, is carried out taking into account the qualitative characteristics of the soil:
- loams;
- sandy;
- clayey;
- mixed.
The level of heaving and the depth of soil freezing depend on this. If the freezing depth is less than the ground level, then there is no need to make adjustments for soil characteristics when planning.
The calculation is carried out with adjustments for soil type and possible subsidence of soft soils.
The data obtained most often forces one to abandon the construction of a strip structure, since the associated work will be very labor-intensive and require significant material costs.
A variety of foundations and the correct choice of the desired design
Slab foundation is suitable for clay soils with high groundwater level in a shallow version
What kind of foundations are needed for houses, if groundwater is close, is chosen depending on the various features of the site itself on which construction is being carried out. A foundation on water is a structure that should ensure the stability of the building, its durability and reliability. To do this, it is necessary to take into account both the quality of the soil and the upcoming loads coming from the building.
Construction of a foundation on clay soils with a high groundwater level involves the construction of any type of foundation:
- belt, the trenches of which are deeply buried;
- pile;
- slab (shallow).
The strip base requires the creation of a monolithic reinforced concrete structure located under the external and internal load-bearing walls.
The depth of the trench must exceed the freezing height
First of all, markings are made on the site, according to which they dig trenches for the strip foundation. Their depth must exceed the freezing height. The calculation is carried out adjusted for weather conditions (temperatures in winter time) and soil.
If groundwater is close, and construction is to be carried out on clay, a strip foundation will perfectly replace a “floating” one. monolithic slab. The weight of the building is evenly distributed over the entire surface of the slab, which is laid on a sand and gravel bed.
Before making such a foundation, you will need to remove soil from the entire area of the future foundation. The pit is dug to a depth 50 cm greater than the thickness of the slab. The calculation is based on the soil freezing depth.
Pile foundation of the house - best option creating a high-quality reliable foundation on clay soils.
By changing the parameters of the piles, it is possible to install supports on hard rocks that are not subject to destruction under the influence of groundwater.
To carry out work in an area with high groundwater level, it is necessary to calculate the load on each individual pile.
Construction of various types of foundations
If groundwater is close to the foundation site, then before you begin constructing a slab foundation, you will need to prepare ditches along the entire perimeter of the future building. It is better if it is a trench 20-30 cm wide and at least 50 cm high (depth). The ditches will be filled with rain or melt water, and thus drainage will be carried out. For more information about the preferred type of foundation, watch this video:
To protect the foundation walls, treat them with waterproofing mastics
The “floating” slab does not lie on clay soil, but on a cushion created from sand and gravel. This type of foundation must be poured by building it on bulk soil. Before pouring, install a drainage system, laying drains at a slope of at least 5 cm for each meter of pipe. To protect the slab, it is necessary to line the inner surface of the base with waterproofing materials. Most often, roofing felt is used, laying overlapping sheets 10-15 cm wide. Fastening is done using bitumen.
A reinforcing frame is laid on the waterproofing and filled with concrete, the filler for which is fine gravel. It is better to fill the entire base in one day.
A strip foundation requires careful preparation of the pit trenches. They must be deep and wide enough to exceed the freezing depth of the ground and allow the formwork structure to be assembled efficiently.
The monolithic tape is poured, taking care of the correct filling of its bottom, high-quality compaction and installation of waterproofing. A frame is installed inside the formwork, connected from reinforcing bars of various sections. Concrete is poured in layers with mandatory compaction of each layer. Useful tips when building a house on soil with high groundwater level, watch this video:
The pile grillage foundation is recognized as the most reliable when constructing buildings in areas with high groundwater level. When making such a foundation, it is important to follow soil indicators, depending on which the size of each of the piles used is determined. Piles are used:
- screw;
- bored;
- driving.
Screw structures can be installed independently without the involvement of heavy construction equipment. After installing all the piles, a grillage is assembled on them or a beam is laid, which is necessary to tie the entire structure together.
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High groundwater: columnar foundation
Construction of a foundation at a high groundwater level is the most important question, arising during the construction of the underground part of the building. It requires the correct answer, which will determine not only the comfort of use, but also the durability of the building.
There are a lot of criteria that need to be taken into account when independently selecting the type of foundation, and we will try to outline them in detail. The video in this article on the topic: “High groundwater level: what kind of foundation should I make?” will help you cope with this task.
What to consider when choosing a foundation
The concept of “high groundwater level” can also be relative. If the water is two meters from the surface of the earth, and you want to build a house with a basement, then this is already an obstacle to construction, and there is a real threat of flooding during operation.
- In this case, the basement can be buried only halfway, or even limited to the ground floor. For the construction of other buildings: summer kitchen, temporary sheds, barn, garage, this level of water is not a hindrance at all, if, again, they do not have a basement.
- But there are situations when the water is very close to the surface, and then any construction becomes problematic. Of course, there are various technologies for reclamation, water reduction and soil strengthening. Another question: “What will the price of the object be?”
Heavily buried strip foundation with high groundwater level
- In order not to come to such a sad result that you see in the photo above, do not rush to purchase building materials and begin excavation work. First you need to correctly assess the hydrogeological situation on the site.
If you cannot do this yourself, seek advice from an appropriate specialist.
This will help you take the right step regarding the construction of the foundation, and will save you from regrets about wasted funds. And they can turn out to be considerable when we are talking not about a bathhouse or a garage, but about a house.
UPG and GWL marks
So, the choice of foundation at a high groundwater level determines the cost of the structure. The right approach will allow you to avoid unnecessary investments, including labor costs.
Therefore, first collect all the necessary information about your site, and only then decide what and how you will build:
- Finding out the groundwater level is not difficult at all; on our website you will find more than one instruction on this topic (read How to find out the groundwater level). As for the level of soil freezing (SFR), each region has its own level.
- Just note that within one area these numbers may vary, depending on the type of soil. Clay soils freeze the least. Then come fine sands, followed by coarse sands and sandy loams. On rocky soils the level of freezing is highest.
- The GWL and UPG indicators must be compared, and if it turns out that the water lies above the freezing level, then the soil is also susceptible to frost heaving. This is always fraught with consequences, and in the example presented you can see how this can end. If there is a danger of soil heaving, you need to choose a foundation option that will have minimal contact with it.
The impact of frost heaving on the foundation
- In such a situation, a strip foundation may generally float up. The best solution to such a problem could be a house on stilts - this is not the cheapest, but it is the most reliable option (see Groundwater is close: how to build a house on stilts).
It is clear that for a small building such as a barn, no one will drive concrete piles. There is a special technology for this case: Tise foundations, and we will talk about them in a separate chapter. - In the southern regions, where there is practically no frost, houses are often built on a shallow or above-ground strip foundation, with a thick drainage layer of crushed stone and sand under its base. But, in some areas there are no quarries nearby where they could be purchased at a reasonable price.
Delivery of sand and gravel mixture from afar greatly increases the cost of the zero cycle, especially if the thickness of the fill has to be increased. A columnar foundation is much more economical, and building it with your own hands is not that difficult.
As you understand, there is no single recipe for all occasions. Our task is to tell about possible options, and yours is to do right choice.
Shallow strip foundation
Whatever you say, the strip foundation in private construction firmly holds the palm. There are not so many areas where groundwater comes directly to the surface, and if its level is at least at a depth of 1-1.5 m, then it is quite possible to make a shallow foundation, or simply a ground one.
- This option is not suitable for every building - its number of floors and the materials used in construction also matter. After all, there is a difference: a one-story house is being built from cellular concrete, with a wooden beam ceiling, or a brick mansion with two or three floors, with concrete floors and stone cladding. The loads here are completely incomparable, and the foundation must be designed for them.
Ground strip foundation with high groundwater
- In terms of cost, a shallow foundation is the least expensive. This is facilitated by the small volume of excavation work, the absence of a basement, which means savings on wall material. In order to build a bathhouse or temporary shelter, this is generally the best option.
- For a house, even a one-story one, it is still better to make a buried, albeit slightly, foundation - it is much more reliable. Sometimes it even works out cheaper, since there is no need for formwork. But this is only the case when you do not have to deal with loose soil. For him, the best option is driven piles.
- If the soil is dense enough, the trenches in it are smooth, with good geometry, and their walls serve perfectly as formwork when pouring foundations. Simply, so that the cement laitance from the concrete does not go into the soil, the excavations are covered with two layers polyethylene film, gluing the joints with tape.
Slight deepening of the strip foundation
- This film serves as additional waterproofing of the structure, but before covering it, the bottom of the trench must be covered with a 10-15 cm layer of sand and gravel mixture. It is impossible to make external coating waterproofing of such a foundation, so it is necessary to add a water-repellent additive to the concrete.
The height and width of the foundation strip must be determined by calculation. This takes into account the type of soil, the likelihood of heaving, expected loads, climatic conditions of the area, and, of course, the landscape of the site allocated for construction.
Types of formwork
If there are slopes or bends in the terrain on the site, it is not recommended to pour the foundation without formwork. How can you get out of this situation and avoid unwanted excavation work, since it is simply impossible to dismantle the formwork in a narrow trench?
In this case, there are various options for permanent formwork: from flat slate to foam panels.
Arrangement of permanent foam formwork
- If we proceed not from considerations of economy, but from the strength of the structure, blocks made of expanded clay concrete or polystyrene concrete can also serve as a material for permanent formwork. Brick is also perfect: be it solid, or hollow, or used.
- These materials are laid in a trench in the form of two parallel walls, between which reinforcement is installed and concrete is poured. If blocks or bricks have through-holes, they are laid flat so that concrete can fill the empty spaces.
- The walls of houses are often built in the same way, only they are reinforced differently, and instead of concrete, the cavities are filled with loose or foam insulation. This method is called well masonry.
- It is most convenient to use it in a narrow trench, since its walls do not allow bricks or blocks to move. When such a foundation is made in a spacious pit, formwork also has to be placed under it.
Schematic diagram of a shallow foundation
The depth of the trench for the foundation of a small country house, or another building may be, for example, 40 cm. In the case of residential building, the height of the support strip must be at least 70 cm, and if the groundwater level does not allow it to be completely buried, the upper half of the foundation may well rise above the surface.
Pile foundation TISE
In order to build a massive building on problematic soil, best option than a pile foundation cannot be found. Use hammers or screw piles- an expensive pleasure.
This requires special equipment and a team of specialists, because it is simply impossible to drive piles and cut off their heads at one level on your own.
- The TISE foundation at high groundwater levels is the most preferable option. It will almost double the cost of the foundation part of the building, including through the use own strength.
This technology got its name from the name of the tool used for excavation work. This is exactly what you see in the photo.
Manual drilling tool TISE
- TISE is a drilling tool, very similar to a garden auger. The difference in their design is only in one detail. It is a plow on a rotating lever that allows you to expand the lower part of the drilled well. Thus, the base of the pile expands, increasing the support area.
- So, there is no need to drive a pile driver into the site - in this case everything is done manually. In its structure, the TISE foundation is not particularly different from a conventional pile foundation. It also looks like a pile field, with a grillage crowning it that does not touch the surface of the ground.
- Naturally, this design must also be calculated for loads. The spherical expansion of the supporting part of the piles improves the bearing capacity of the foundation as a whole, which makes it possible to use this option not only for the construction of relatively light frame-panel buildings, but also for houses made of brick and stone.
Pile foundation with high groundwater levels
- It is this expanded part of the foundation pillar that provides it with unshakable strength when the forces of soil heaving push it to the surface. Thanks to this stability, the pile field can stand through the winter without load, which should never be allowed when installing a strip foundation.
Building placed on foundation pile type, is not subject to seasonal shrinkage at all. For a wooden house this is not so important, since wood bends well.
But stone and brick walls with frosty heaving of the soil can simply crack from floor to ceiling. And this becomes a problem - the supporting structures need to be repaired, and new finishing will have to be done.
Some details of the technology
In the process of designing a pile field, depending on the expected loads, the dimensions of the piles and their location points are calculated.
After all, you need to know their diameter and length, the distances between them, location options, places of reinforcement:
- On average, the step between piles is from 1.5 to 2 m. The depth of their placement is also within the same digital limits, but it should not be less than the UPG mark.
The essence of their device is this: a spatial frame of four to five D-12 mm reinforcement rods connected with steel wire is installed in the drilled wells.
TISE foundation reinforcement
- Then a cement-sand mixture is poured into the well, with a ratio of dry components of 1:4. If this is a small building such as a barn or garage, you can even save a little by putting cement and sand 1:5. But when building a house, it is better not to reduce the amount of cement, and even make the ratio 1:3.
- Simply, for pouring it is better to use not Portland cement, but gypsum-alumina cement. When moistened, it spontaneously expands, filling the smallest pores in the walls of the well.
Such cement allows you to reduce the consumption of the solution, which will not be strongly absorbed into the soil - it is what drillers use to plug wells. - If you work with ordinary cement, you need to use formwork in the form of a metal pipe, which can be removed after the concrete hardens, or a piece of roofing felt rolled into a tube. You can also take asbestos-cement pipes, which will act as permanent formwork, which is what you see in the photo below.
Formwork for monolithic piles and grillage
- The solution poured into the well is carefully compacted using the bayonet method or using a deep vibrator. At high location groundwater, certain difficulties arise in concreting.
And here, the faster the well is filled with solution, the less time the water has to seep into it. Otherwise, you will have to pump out the water with a pump.
For ease of work, wells are drilled in groups of 4-5. At the same time they are reinforced and then concreted.
First, the expanded segments of the prepared wells are filled and compacted, and then their trunks. As for concreting the grillage, this technology is similar to the process of pouring a strip foundation.
When building a foundation on heaving soil, it is necessary to take into account permanent and temporary impacts on the soil. In winter, the soil affects the soil with a vengeance, and this is associated with heaving. Modern technologies make it possible to bypass heaving and build a reliable foundation.
Soil heaving is an increase in soil volume during the transition from a thawed state to a frozen state and a sharp decrease in volume when frozen soil thaws. Heaving depends on the composition of the soil, groundwater level and soil porosity. When freezing, the water in the soil increases by 10-14%, the soil heaves and can lift a building.
Heaving soils include fine and silty sands, all types of soft plastic soils (sandy loam, loam). The groundwater level openly affects the heaving of the soil. If the water is closer to the surface, then the impact of heaving forces on the structure is 2-3 times stronger. The finer the soil structure, the faster the soil will become wet.
The foundation laid at the level of soil freezing can be seriously damaged. Even with a significant weight of the building, it can rise when the soil heaves. When the soil thaws, the soil sinks and the structure sags unevenly. The walls begin to warp, and after 5-7 years the foundation will completely fail to comply with building codes.
Ways to combat soil heaving 
- Replacing heaving soil. This method is the most effective. When laying the foundation, the soil is removed to a depth of 50-70 cm, and crushed stone and a sand cushion are poured in its place.
- Removing moisture from the soil. To protect the soil from heavy rainfall, a blind area is constructed along the entire perimeter of the foundation. The width of the blind area should be wider than the backfill so that water does not penetrate under the foundation.
- Soil insulation. To combat heaving, you can insulate the soil near the foundation. If the ground freezes to 1.5 meters, then insulate it with a 1.5 meter wide strip around the perimeter of the house.
When building a foundation on heaving soil, take into account the change in groundwater in different seasons. In different regions, water rises to different heights.
Options for laying a foundation on heaving soil
When choosing a foundation, it is necessary to take into account the forces of soil influence and calculate the mass of the building so that the foundation does not crack.
- Strip recessed foundation Rarely used on heaving soils. The depth of laying such a foundation should not be higher than 1.5 meters, otherwise heaving forces will directly act on the foundation. This type of foundation is laid under heavy stone and brick houses. If the structure involves the use of concrete blocks and wood, then a buried strip foundation on heaving soil can behave unpredictably, for example, lifting the building and warping the walls.
- Shallow strip foundation widely used on heaving soils, as it is laid above the freezing depth. This type is suitable for houses made of timber, logs and concrete blocks. The installation of such a foundation is carried out in a frozen layer of soil. This foundation is highly reliable and durable for buildings with low weight.
- Pile foundation on heaving soil it is used if the depth of soil freezing is no more than 1.5 meters, and a frame type of frame is used. The size of the piles is from 3 to 4 meters. Such a foundation is a stable foundation, but its laying will require special equipment. In private construction, screw piles are used that are screwed into the ground.
- Columnar foundation optimal for heaving soil. Its ease of installation and cost-effectiveness are the main selection criteria. A columnar foundation is laid in the freezing layer of soil using pillars. The distance between pillars should not exceed 2 meters.
The foundation cannot be left idle; it is immediately loaded, distributing the load vertically across the supports using a level. The pillars are laid on a screed of sand and cement.
Using as pillars reinforced concrete structures you can lay the foundation on the ground:
- with high moisture levels;
- moist and heavily moistened;
- swampy.
Foundation settlement
Building settlement can be facilitated by uneven distribution of load on the foundation. If there are blank walls in one part of the house, and only arched ones in the other, then the weight presses on the foundation with different forces, cracks appear in the foundation, and the structure warps.
Some features of the construction of the building also affect settlement. The part of the house built in the summer will sag less than the part completed in the winter. To avoid uneven settlement, it is better to build a building at one time of the year, or use light types of materials in winter.
Construction on heaving soil is a complex process that does not allow for mistakes. Compliance with measures to protect against heaving forces will protect the building from destruction and distortion of the structure.
Foundations - the basis engineering structures ensuring their strength, stability and durability. It is important that the soils in the base have the required strength and low compressibility. To determine the soil characteristics and conditions for laying the foundation, a complex of engineering-geological and hydrological surveys is mandatory.
Of particular importance are:
- type of foundation soil;
- location and thickness of layers;
- the depth of seasonal freezing;
- groundwater level.
One of the effective methods for constructing a foundation with the required characteristics is to replace unreliable soils.
Heaving or swelling rocks
Heaving foundations are characterized by the property of increasing in volume when freezing, which leads to a rise in the soil surface and the occurrence of frost heaving. Subsequent thawing leads to the opposite effect - soil precipitation. The result is the appearance and development of cracks in the foundation structure and walls of the building, the tilt of the structure and even its destruction.
Heaving types of rocks - fine and silty sands, loams, clays (with high humidity at the time of freezing).
The construction of foundations on such soils is dangerous, so the heaving soil under the foundation is replaced with non-heaving soil (coarse or medium-grained sand, gravel, crushed stone).
Soils are considered non-heaving if their degree of heaving is ≤ 0.01, that is, when they freeze to a depth of 100 cm, their size increases by ≤ 1 cm.
It is not always advisable to replace the soil at the entire freezing depth, because it is known from practice that freezing in the lower third of the layer is insignificant and practically does not lead to heaving. Therefore, it is enough to replace only the upper two thirds of the layers.
But only a qualified specialist can give the correct conclusion in each specific case.
If the house is heated in winter, then it is enough, simultaneously with replacing the foundation soil, to fill the sinuses with draining soil. This will reliably protect the foundation structures from lateral soil influences. If heating is not planned, then backfilling is carried out outside and inside.
It is unacceptable to install a sand cushion if, within its height:
- There is a variable groundwater level. The pillow works as drainage, turning into the appearance of ordinary heaving soil;
- there are groundwater pressure, and the foundation base is made at a depth above seasonal freezing. Under the influence of water pressure, sand heaving may occur.
Peat types of soils
Replacing peat is economical if two conditions are met:
- its thickness does not exceed 2 m;
- Under the peat there is a layer of fairly strong rocks.
Otherwise, you should think about the need for construction in this area or proceed to the construction of a pile or slab foundation.
Rocks
Durable rock has excellent load-bearing capacity, resistance to frost heaving and immunity to temporary flooding. Replacement of rocky soil under the foundation is necessary only if there are upper cracked layers. After dismantling them, concrete is laid on top.
A characteristic feature of heaving soils is their susceptibility to frost heaving.
The process of soil heaving is the result of the freezing of moisture in it, which turns into ice.
The force of heaving in clay soils can destroy any structure, so construction on such soils requires a special technology for the work.
Since ice is less dense than water, its volume is greater. Heaving soils include three types of clay soils: sandy loam, loam and clay. Clay contains a lot of pores, which allows it to retain moisture. Accordingly, the more clay and water contained in the soil, the higher its heaving.
The degree of frost heaving is understood as a value indicating the susceptibility of the soil to possible heaving. The degree of heaving is determined as the ratio of the absolute change in soil volume as a result of freezing to the height of the soil before freezing occurred.
Thus, here it is possible to determine how the freezing process of the soil affects its volume. If the index of the degree of soil heaving is more than 0.01, then such soils are called heaving, that is, increasing by 1 cm or more when the soil freezes to a depth of 1 m.
Anti-heaving measures
The heaving force is so great that it can lift a large building. Therefore, on heaving soils, special measures are taken to reduce and prevent heaving. The following measures taken against soil heaving can be distinguished:
All clayey soil types are susceptible to heaving.
- Replacing the soil with non-heaving coarse or gravelly sand. This will require a large pit with a depth exceeding the freezing depth of the soil. The heaving layer of soil is removed from the dug pit, which allows sand to be poured in and compacted thoroughly. Material such as sand is very suitable for installation, as it has a very high load-bearing capacity. This method is expensive because it requires a large amount of work.
- You can also achieve stability by laying it on heaving soils at a level lower than the freezing depth. In this case, heaving forces will act only on its side surfaces, and not on the base. Freezing to the side surface of the base of the house, the soil will move it up and down. As a result of the load, the heaving force per 1 sq.m of the side surface of the base of the house can reach 5 tons. If a house built on has a base equal to 6x6 meters, then its side surface area will be 36 square meters. meters. The calculation of the tangential heaving force when laying to a depth of 1.5 meters will result in 180 tons. This is sufficient for wooden house rose, since the tree will not be able to resist the force of heaving. Therefore, this method is used for the construction of heavy houses made of brick or reinforced concrete blocks. They are built specifically on tape types.
- To reduce the influence of the tangential force of soil heaving, a layer of insulation is used, which is laid on the soil layer. This method is suitable for light buildings and shallow ones. The thickness of the insulation used is taken into account depending on the climatic conditions of the place where the house is built.
- Measures can be taken to drain water to prevent heaving. For this purpose, a drainage system is being installed along the perimeter of the site. To do this, at a distance of half a meter from the foundation to the depth of its laying, a ditch of similar depth is laid. A perforated pipe is placed in it, which must be laid in the filter fabric while maintaining a slight slope. A ditch with a pipe wrapped in fabric must be filled with gravel or coarse sand. The water flowing from the ground should then flow through the drainage pipe into the drainage well through the hole. To ensure natural drainage of water, a sufficiently low area for drainage is required. This requires the installation of a blind area and storm drainage system.
Strip base device
General requirements
The basic rules for constructing the foundations of buildings and structures are set out in SNIP 2.02.01-83.
For installation, it is necessary to create a structure that would have an acceptable level of deformation throughout the life of the house. In this case, the condition of high stability under the influence of the tangential force of soil heaving must be met. The indicator of their deformation when laid on heaving soils should be zero. To ensure that the base of the foundation does not come off the base of the building, when laying it, they follow the rule adopted in SNiP 2.02.01 - 83. Estimated freezing depth in relation to the laying depth for soils:
- non-heaving - does not affect the depth of placement;
- weakly heaving - exceeds the depth of placement;
- medium and highly heaving - less than the depth of its foundation.
This rule eliminates the action of large normal heaving forces on the base of the house for medium and highly heaving soils. For those with low heaving, the effect of heaving forces is insignificant. The acting tangential forces of heaving on the side surfaces of the foundation are crushed under the influence of the weight of the entire structure. Therefore, the heavier the construction project, the more feasible this condition is.
Application of strip structures
The foundation, being underground part building, takes the load from the weight of the structure and transfers it to dense layers of soil, that is, the base. Its edge is a plane located in the underground upper part, which is in contact with the sole or base of the foundation.
Tape has high reliability and durability, therefore it is widely used in construction.
Device strip foundations easier than others, although it will require a lot of materials and the use of a truck crane. The tape is a reinforced concrete strip laid under the walls of a building along its perimeter. When laying, it is necessary to ensure that the cross-section in each section is of the same shape.
This type is used for the following types of houses:
- with walls made of stone, brick, concrete, with a density of more than 1000-1300 kg/cu. m;
- with monolithic or reinforced concrete, that is, heavy floors;
- with a planned basement or ground floor, in which the walls of the basement are formed by the walls of a strip foundation.
Application of tape reinforced foundation ensures the reliability of the structure of the walls of a house built on heaving soils. At the same time, it redistributes the load from an area with one type of soil to an area with another type.
Kinds
Device diagram
Strip foundations are divided into two types: buried and shallow. This division depends on the load of the load-bearing walls of the building on their underground foundation. Both types are suitable for construction on heaving and slightly heaving soils, providing sufficient stability to the building. The strip foundation forms a reinforced concrete frame that runs along the entire perimeter of the building structure. The construction costs of this structure make it possible to achieve the optimal “reliability-savings” ratio. The budget for the device will be no more than 15-20% of the cost of construction of the entire structure or building.
For the construction of buildings on slightly heaving soils, a shallow foundation is suitable. This type is used for the construction of foam concrete, wooden, small brick and frame houses. It is laid to a depth of 50-70 cm.
Recessed strip foundations are suitable for the construction of structures on heaving soils. The floors and walls of houses for such a foundation must be heavy, and the weight of the entire structure will prevent the soil from heaving under the weight of the building or structure.
For houses built on heaving soils, a simultaneous construction of a basement or garage is planned. Laying is carried out to a depth of 20-30 cm lower than the freezing depth of the heaving soil. The material consumption for the second type will be greater than for the first. Under the internal walls of the building it can be laid at a depth of 40 to 60 cm.
The bottom of the deep strip foundation is laid below the freezing level of water in the soil. This can explain high strength and stability compared to shallow. However, the labor and material costs for the recessed type are higher.
Device on heaving soils
A concrete mixer will help speed up the process of preparing the concrete mixture.
The strip foundation is laid in the warm period of the year. Laying does not require the use of expensive types of equipment; only a concrete mixer and small mechanization are used.
Intumescent and deeply frozen soils are not suitable for laying strip foundations. In such soils, its installation is carried out in rare cases. The area where a strip or other type of installation is planned must undergo a series of geotechnical surveys. These should include:
- Determination of soil type and its condition.
- The degree of soil freezing.
- The presence of water contained in soils.
- The magnitude of the load from the building structure.
- Availability of a basement.
- Service life of the structure.
- Necessary materials for installation.
- Equipping the site for the construction of underground communications.
A responsible and competent approach to choosing the type for a future structure determines its quality. The future depends on it performance characteristics building. During the construction process, unexpected costs may arise to correct errors as a result of distortions. Load-bearing structures can be subject to vertical and horizontal deformations and uneven precipitation occurring in the soil. Groundwater problems may arise.
Laying a recessed strip foundation
Preliminary stage and preparation of materials
Recessed strip foundations are structures with thick walls, the thickness of which is determined by the material used. The thickness of the walls is influenced by the pressure of the building and the degree of freezing and soil moisture. The strip foundation can be designed with an expansion towards the bottom or have a stepped appearance.
The design of the device on heaving soils is divided into two types:
The block strip foundation is mounted using special lifting equipment.
- Precast strip structures can be built using prefabricated concrete blocks. Among the advantages of this type is the possibility of construction in any season. Such a foundation is simple to install on heaving soils, which can be done in a short time. The disadvantage is the high price of the structure and the possibility of moisture transmission in conditions of insufficient waterproofing. This requires a blind area and drainage.
- Monolithic type belts are built from high quality concrete mortars. Their designs, of any complexity, are equipped with a reinforced frame embedded in a single monolithic strip. The disadvantage of the design is the long duration of the masonry process.
During the preparatory work for laying a strip foundation installed on heaving soils, it is necessary to take into account the following points:
The wooden formwork of the foundation must be securely fixed so that it does not collapse under the pressure of poured concrete.
- The width of the base should be 15 cm greater than the width of the building walls taken into account during the design.
- Eliminate possible downtime by drawing up a work plan when making a belt type with your own hands.
- Equip warehouses by importing necessary materials to the construction site to pour the structure in one go.
- Be sure to fix the position of all elements of the strip foundation using a cord with stakes.
- Level out in advance all uneven terrain at the site of the future foundation using slats and a level.
So, to lay a recessed strip foundation you will need the following tools and materials:
- Level.
- Knitting wire.
- Bayonet and shovel shovels.
- Cord for marking.
- Ribbed reinforcement (section 10-14 mm).
- Lumber, axe, hammer, nails and hacksaw for formwork.
- Cement, sand, crushed stone.
- Concrete mixer as equipment.
Step-by-step installation
The walls of deep trenches must be strengthened with spacers to avoid soil collapse.
The laying procedure involves performing the following work:
- Layout of the plan of a building or structure.
- Determining the required depth.
- Preparing the trench.
- Laying a bed of gravel and sand if necessary.
- Installation of formwork.
Before starting work, after clearing the construction site, a layout of the building or structure is laid out. In this case, all dimensions of the planned foundation are transferred from the finished drawings to the surface of the land plot. Pillars are installed, serving as cast-offs, located at a distance of 1 to 2 meters from the future walls of the house, from which boards are nailed. These boards mark the dimensions of the pit trenches, as well as the foundation and walls of the house. Distances are measured with a tape measure to ensure accurate measurements, and angles are calculated using a triangle. They determine the location of the perpendicular axes.
Construction begins with the installation of a sand cushion at the bottom of the trench.
For heaving soils, it is very important to determine the depth of their freezing, the presence of groundwater, and calculate the soil load on the foundation. It is laid at a depth below the freezing point of heaving soils, therefore it is buried.
Laying technology on initial stage associated with digging a trench. You can prepare it using an excavator or with your own hands using a shovel. The trench will be the foundation, which must be made level at the end of preparation without collapses or unevenness. A trench is dug up to 1 meter deep, without installing fasteners. Its walls must be vertical. If the depth is more than a meter, then slopes are made to prevent soil from falling out from the spacers.
The finished trench should be laid with layers of gravel and sand, each 12-15 cm high. After laying, both layers are compacted using water. The finished pillow is covered with a layer of polyethylene film. An alternative option is to pour the concrete solution, which is kept for a week. As a result, the thinner concrete mortar sets firmly.
Formwork preparation stage and reinforcement tying
The diameter and number of rows of longitudinal reinforcement in the frame depends on the design of the structure being built.
To construct the formwork, planed boards are taken, the thickness of which is from 40 to 50 mm. Can be used panel formwork, moistened with water before pouring the concrete solution. Slate, plywood and other suitable materials are used for this purpose. While erecting the formwork, it is simultaneously controlled to the correct level of verticality. For the plant, asbestos concrete pipes are laid in the formwork of the sewerage structure with water supply.
As the formwork is constructed, a reinforced frame is laid into it. The reinforcement is mounted in the formwork, creating a frame around the entire perimeter of the future foundation. The reinforcement bars used must have the same diameter everywhere. The reinforcement frame is mounted using knitting, which must be done in accordance with the design documents. When installing it, carefully follow the technology of the device of the selected type, prefabricated or monolithic.
In the absence of a special project, a standard reinforced frame is constructed in a vertical position. Two rows of reinforcing bars are taken along the width of the foundation, which are fastened horizontally using knitting wire. Required amount reinforcement is determined by the width of the foundation and is carried out every 10, 15 or 25 centimeters.
Pouring the structure
To compact the concrete mixture placed in the formwork, an internal vibrator should be used.
After preparing the formwork and tying the reinforced frame, concrete is poured. The thickness of each layer of fill should be about 15-20 cm. The fill should be compacted with a special tamper made of wood. So, in order to eliminate all voids in the structure, the walls of the formwork are tapped using a wooden hammer.
The concrete solution is prepared on site using a concrete mixer. In this case, cement, sand and crushed stone are taken in a ratio of 1:3:5, respectively. This composition varies depending on what time of year and how complex the structure is.
The consistency and composition of each layer should be the same. In winter, they use a concrete heater, covering the entire structure mineral wool and using special frost-resistant additives. Concrete is poured from a small height using gutters, otherwise the pouring may end in concrete delamination.
To remove air from concrete, at the end of all pouring work it is pierced in different places using a probe. To make the strip foundation evenly strong, it is covered with film.
At the final stage, the formwork is removed 4-6 days after the concrete is poured. The period depends on the temperature at which the pouring was carried out and on its thickness. After removing the formwork, backfilling is carried out using clay and sand. The backfill is compacted with water and leveled.
In the upper part, the foundation is treated with a special waterproofing solution. The type of composition depends on how deep the structure lies. Thermal insulation is carried out if necessary.
When installing a recessed strip foundation on heaving soils, the freezing depth is taken into account, which is a constant value for each settlement. It depends on climatic conditions and humidity levels. Unlike a shallow foundation used for slightly heaving soils, a buried foundation does not include a sand cushion. The support for buried strip foundations is the unresolved structure of the soil, which is not waterlogged.
Shallow on heaving soils
The construction of buried strip foundations in areas with heaving soils is expensive. It requires large financial costs. The increased influence of the tangential heaving force on the structure, exceeding the load from the structure itself, complicates the construction technology. Therefore, the most promising solution is the construction of basement-free low-rise buildings on heaving soils. Such buildings are characterized by the use of strip monolithic reinforced concrete shallow foundations. They require an anti-heave sand cushion. At the slightest load from the house, its foundation rests on the soil, which is close to the surface. Due to the absence of the need for additional measures, the costs of installing this type of foundation are significantly reduced.
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