Options for building a foundation on clay soils with high groundwater levels. Which foundation is better for a house with high groundwater levels? Groundwater for which foundation to build

The main function of the foundation is to accept and distribute the load of the structure. When deciding on the choice of foundation type, soil characteristics and groundwater levels or groundwater levels are taken into account. A solid foundation with a high level of groundwater on the site requires large expenses for its construction, and can cause many problems.

In fact, very often developers have to deal with waters that lie quite close to the surface. Most often, this problem is aggravated by the presence of clay in the soil.

In such a situation, it is hardly possible to construct a basement, since the foundation will be subject to significant pressure from forces caused by soil heaving. Laying foundations in conditions of nearby groundwater will require compliance with certain rules that can minimize the impact of this unfavorable factor.

Harmful effects of high GWL

Since the main component of any foundation is concrete, the issue of the harmful effects of water on this material should be considered. Essentially speaking, the destructive effect on concrete is carried out not by the nearby water itself, but by salts and other chemicals dissolved in it. Builders have the term “cement bacillus,” which loosens the hardened mortar and causes it to delaminate. Very often you can visually assess the beginning of the destruction of the base: the appearance of plaque, stains or a musty smell.

Already at the stage of preparing the pit, some difficulties arise: due to incoming water, the bottom is washed away, significantly reducing the bearing capacity of the soil. In this case, the construction of the foundation will have to begin with the laying of a drainage system and drainage of water. Otherwise, deformation of the poured base and subsidence are inevitable.

Ascending suffusion is the process of leaching mineral compounds from the soil, which can be observed at a construction site with a high groundwater level. In order to minimize the dangerous impact of suffusion on the foundation of a building, comprehensive work to drain the building site is necessary.

There is another way to avoid exposure to hazardous factors - the use of pile technologies or prefabricated structures made of reinforced concrete blocks. The disadvantage of using them is the increased cost of laying the foundation in close waters.

How to independently determine the ground level

You can determine what water level in the area is by contacting the relevant city organizations, but you can measure it yourself. To do this, you need to make the following measurements in the fall or spring:

• prepare a hole with dimensions: depth – 3 meters, width – 1 meter;
• cover it with polyethylene to protect it from possible precipitation;
• after some time, measure the depth of the accumulated water;
• with a depth of less than 2 meters, we can conclude that the groundwater level on the site is moderate and does not require additional measures when constructing the foundation.

If the water level is below two meters, you will have to choose a more reliable type of foundation, install a drainage system and carry out waterproofing work.

The ratio of UPG (soil freezing level) and GWL

In accordance with the requirements of SNiP: if the GWL indicator is less than the UGL, then there is no need to take into account the type of soil. The foundation in this case is calculated only for the load of the house being built.

However, when erecting a structure on mixed soils, sandy, clayey and sandy loam soils, and when a high water level is detected, the foundation is laid to a depth below the freezing level. In such a situation, the installation of a drainage system is mandatory.

In addition, a correction is given for groundwater level: from 0.5 - 1.0 meters upward. This increase is due to established construction practices. And it also excludes the possibility of constructing a strip-type base due to its cost.

If the groundwater level is high, it is necessary to take into account the very likely subsidence of weak soils when performing drainage.

If seasonal flooding is possible, it is preferable to use reinforced concrete structures with piles buried below the level of expected erosion.

Foundation construction technology

After preparing the pit, taking into account the depth of the foundation, the construction site allocated for its construction is drained and leveled. For this purpose, a ditch is prepared with a depth of 0.3 meters and a width of 0.2 meters with a retreat from the perimeter of 0.5 meters. This ditch will serve for storage and drainage. Construction of the foundation in groundwater is unacceptable due to erosion of the solution, and, consequently, weakening of the slab. Next, perform the following work:

1. The soil on the site is compacted and concrete preparation is carried out. A layer of concrete up to 25 mm is laid. This will level the surface and allow you to begin waterproofing work.
2. After the solution has hardened, it is overlapped with a double layer of rolled waterproofing materials (roofing felt), which are then secured with bitumen.
3. The mesh reinforcement for pouring is being installed. The thickness of the slab can range from 15 to 30 cm, but the thicker it is, the better the foundation will perform its immediate function.
4. Once the concrete has been poured and completely cured, the process of laying the blocks begins. After this process is completed, a kind of monolithic well is obtained.
5. Protection is provided from the effects of nearby groundwater.

The type of foundation structure discussed above is one of the most expensive, but undoubtedly one of the most reliable.

Layer-by-layer foundation protection

There are three types of layer-by-layer protection of foundations that successfully solve issues of protection from nearby groundwater:

1. Bitumen mastics with additives of rubber and polymer components make it possible to obtain a smooth, moisture-proof layer. It is often used in the construction of private houses with a residential basement.
2. Cement-based mixtures are no different in characteristics from the previous type. They harden well, creating a moisture-resistant layer. However, in comparison with mastic, they are less plastic and, when subjected to vibration, can be subject to cracking and reduce performance.
3. Special bitumen films or film waterproofing. They alternately glue the entire foundation in three layers.

Now let's look at what type of foundation can be made with high groundwater levels.

Monolithic slab and pile foundation

This is a type of solid base that evenly distributes the weight of the entire building structure. Despite its good stability during ground movements, it has one significant drawback - the high cost of materials and work.

This is a good solution for regions where groundwater is close, or if there are quicksand. For its construction, various types of piles are used: bored, reinforced concrete and others.

The posts are screwed or driven into solid layers of soil, and their outer part is connected by beams. The result is a rigid structure that can withstand significant loads. The disadvantage of this type is the impossibility of building a house with a basement.

Strip foundation type

Sketch of the correct arrangement of the foundation base

This type is a reinforced concrete strip that can be made under load-bearing walls. This type is most common in the construction of individual houses.

If such a support structure is made, then to protect it, a cushion is made from a mixture of gravel and sand. However, it should be taken into account that it can only be done with good external waterproofing and only if the water level rises from time to time.

Foundation on a “floating” cushion

Which type is better to choose? At high water levels and if they are close to the surface, this type of foundation is the most reliable. When choosing this type of foundation, you must:

• install a drainage system;
• prepare a pit/trench of the required size;
• compact the bottom using a vibrating plate to a height of 40 centimeters;
• if you make a tape above the surface, then its height will be determined by the construction site;
• construct a “floating” pillow. Sand is poured into the trench in layers, with each layer compacted in stages. The height of the finished pillow should be at least 50 centimeters;
• cover the resulting base with waterproof materials;
• backfill with crushed stone (up to 20 cm) and compact well;
• lay a layer of rolled waterproofing on top;
• assemble durable formwork from panels or lumber. Concrete is a heavy mixture, and if the structure is not strengthened with bars and spacers, it may become deformed;
• perform reinforcement in two layers with cell sizes of 20x20, maintaining a distance of approximately 5 cm from the base and top of the formwork structure;
• make tape reinforcement from the same reinforcement. To do this, a frame is made of longitudinal rods tied with transverse elements every 40 cm;
• It is better to pour concrete using a mixer. This will allow workers to complete it in one day;
• take into account the requirements for caring for the hardening slab, moisten or cover it, preventing it from drying out or being washed away by precipitation;
• after the solution has completely hardened, disassemble the formwork;
• treat the foundation with a waterproofing mixture.

The construction of a strong foundation at a high groundwater level can cost developers several times more than conventional foundations. However, if you deviate from the requirements during its construction, you may end up with a poor-quality foundation, and then problems with the entire house.

The construction of a house can occur on almost any type of soil, but when installing a structure on soil saturated with water, it is necessary to carefully select the type of foundation. It is also important to accurately determine the depth at which the base should be installed. The strength and durability of the structure depends on taking into account all the features. In areas where groundwater is too high, screw piles are often installed. A floating monolithic foundation is also often created.

Drainage works on the site

The simplest option for getting rid of water is to raise the area by at least half a meter. But it is worth remembering that carrying out such work requires large expenses. To do this, you need to fill the area with dry sand or soil, and then level the surface using a bulldozer.

A less expensive option is to create a network of canals throughout the site. After such actions, water will collect in ditches. The depressions are created in the form of open trenches, which are reinforced with clay. If desired, you can install gratings on them so that they do not spoil the appearance of the area.

If desired, you can create closed-type ditches, which are asbestos-cement pipes with perforation. When designing ditches, it is worth carefully studying the site to take advantage of the features of its topography. Ditches are created across the slope, as in this case they allow water to be collected more efficiently. It is worth remembering that if the site is located on a plain, it is necessary to make ditches with a slope. But it is important to take into account that the slope should not be more than 5 cm per 10 meters of length.

The drainage system must discharge water into a roadside ditch or into a specially created reservoir.

Features of a monolithic foundation

A monolithic reinforced concrete base is a fairly reliable support for the structure. It helps distribute the load over a large surface, so it rarely collapses. This type of foundation is often used in areas with high groundwater levels. The monolithic base resists soil pressure well during soil heaving.

A classic monolithic foundation should be created if the site experiences a seasonal increase in groundwater levels. This base option allows you to build a basement. If the house is being built in a swampy area or near a pond, it is worth creating a monolithic foundation on a floating pad.

Floating foundation

The specified foundation type is created as follows:

1. First, a pit is created. It is worth remembering that its bottom should be lower than the groundwater level. If this condition is not met, the lower part of the foundation will be in conditions of high humidity. This can lead to gradual destruction.
2. After this, geotextiles are placed at the bottom. This is necessary to prevent mixing of the backfilled sand with the underlying soil.
3. At the next stage, the formwork is installed and sand is poured. The thickness of the layer should be about 20 cm. After backfilling, the sand must be moistened and compacted using vibrating plates.
4. Then gravel or crushed stone is poured onto the sand. The thickness of the poured layer should be 20 cm. After completing the compaction process of the sand and gravel cushion, it is necessary to cover it with waterproofing material. This is necessary to prevent water from the cement composition from entering the soil.
5. Next, the reinforcement frame is created. The reinforcement must be a single structure, all elements of which are securely fastened together. After this, it is important to check the reliability of the created structure.
6. At the final stage, concrete is poured. It is important to ensure that no voids are formed during pouring. Their appearance can lead to the gradual destruction of the foundation. To prevent voids from appearing, a construction vibrator should be used. The surface of the mixture after pouring is leveled with a shovel. In order for the structure to be strong, it is important to pour it in one go, without dividing the concrete into layers. To do this, you need to order a machine with concrete, since you won’t be able to mix a large volume of mortar yourself and pour it right away.

It is worth noting that the monolithic foundation is quite reliable and allows you to create a basement floor. If water constantly accumulates in a dug pit, it must be pumped out using pumps or drainage work must be carried out throughout the entire area to reduce the groundwater level.

Features of a columnar foundation

Such a foundation resists soil deformation well during freezing of groundwater in the area. To create such a foundation, it is necessary to drill holes in the soil into which reinforcement will subsequently be installed. The walls of the pits are covered with roofing felt, after which concrete is poured. The surface of the drying composition is covered with polyethylene. This is necessary to ensure that the concrete does not crack during drying.

It is worth noting that with such a foundation it is impossible to create a basement. In this case, the bearing capacity of the foundation is limited. That is why, when the groundwater level is high on the site, a monolithic foundation is chosen.

Pile foundation

This type of foundation is used to create houses in wetlands, as well as in areas that are located in flooded areas. Examples include the areas around St. Petersburg, Amsterdam and Venice.

When creating such a foundation, piles are driven or screwed into the soil using special equipment. It is best to use screw steel piles coated with zinc to create the base. During installation, they compact the earth, which helps increase the stability of the support. But it is worth remembering that a pile foundation does not allow building a basement.

If you want to create a house with a basement in an area where the groundwater level is high, you should choose a monolithic base on a floating cushion. This option is quite reliable and protects the structure from groundwater.

How to make a floating foundation

The floating foundation pie consists of several layers:

• sunken soil;
• a layer of compacted sand and gravel;
• concrete base, which is a monolithic slab;
• vapor barrier;
• heat-insulating material;
• waterproofing layer;
• reinforced concrete screed.

It is worth remembering that the technology for creating the type of structure described may differ depending on the characteristics of each case. The creation of a foundation is influenced by the type of soil, terrain features and the structure itself. For example, if the structure is massive, the foundation must be created in such a way that it can withstand heavy loads.

The foundation construction process consists of several stages:

1. Creation of a pit. Its dimensions must correspond to the dimensions of the future foundation. The depth of the pit depends on the distance from the soil surface to the groundwater. This parameter is also affected by the level of soil freezing. After creating the pit, its bottom must be carefully compacted around the entire perimeter. It is worth remembering that you should not leave areas filled with sand or moisture.
2. Laying a sand cushion. In cases where groundwater is located too close to the soil surface, geotextiles should be used. This material is laid around the entire perimeter of the created pit. This will prevent the material from washing out. Each layer of sand and crushed stone must be thoroughly compacted using a vibrating plate.
3. Pouring concrete . Concrete grade M100 is usually used for the foundation of the house. The thickness of the foundation should be about 10 cm.
4. Laying waterproofing film. All seams of this material must be sealed. After completing such work, it is necessary to wrap the edges of the foundation film. This will help protect the base and the entire structure from moisture.

It is worth remembering that the waterproofing layer should be created only after the concrete solution has completely hardened. If you wait less than the allotted time, the foundation will be fragile and will begin to collapse already during the construction of the house. The reinforced concrete slab will be laid on the created structure.

Creation of a reinforced concrete structure

To create a foundation, a reinforcing metal mesh is laid on the waterproofing layer, after which the concrete solution is poured. The concrete grade M300 is used for it. After this, you need to wait a certain amount of time until the concrete dries and hardens completely.

If there is a need for this, communications are laid during the pouring of such a foundation. In this case, the pipes must be laid simultaneously with the pouring of the foundation. It is worth remembering that filling should be carried out without interruptions. If this rule is not followed, the strength of the foundation will be low and it may begin to collapse. This is especially important when creating a foundation on loamy soils and in areas with high groundwater levels.

In some cases, when creating such a structure, concrete blocks are laid, which are mounted in the form of supports on a concrete base. But such actions are performed quite rarely, as this increases the cost of the work. However, the strength of such a foundation is not great enough. When creating a prefabricated foundation, it is best to fill the pillars with concrete and then cover them with a layer of rubber, which will protect the base from moisture. If you take into account all the described rules for creating a foundation, you can make a reliable foundation for a house, even if the groundwater is located close to the soil surface.

Materials and tools

Before creating the foundation, you need to prepare all the necessary tools and materials in advance. To create a monolithic floating base you will need:

1. Tools for digging a pit. Before using heavy equipment, it is important to correctly determine the digging depth. If calculated incorrectly, the foundation will be washed away by groundwater.
2. Sand and gravel
3. Vibrating plate. This tool is required if the base is installed on soil saturated with moisture.
4. Polyethylene film, which is necessary to create a waterproofing layer.
5. Vapor barrier membrane
6. Insulation. Often, when creating a monolithic foundation, foam slabs are used. This material does not shrink and is not susceptible to the negative effects of moisture.
7. Concrete solution. It is important to choose the right grade of concrete so that the foundation does not crack under load.
8. Steel rods and tying wire to create a reinforced frame.

At the preparatory stage, it is important to check the availability of all materials and tools so as not to interrupt work while pouring concrete.

In some cases, in addition to the materials described, concrete blocks are used. It is worth remembering that if the groundwater level is high on the site, you can choose one of several types of foundation for the house, rather than focusing on the common option. These include a floating foundation, piled and prefabricated monolithic, which requires concrete blocks. A strip foundation is not created in such areas, since it does not contribute to the uniform distribution of moisture, which is why it begins to deform.

They pose a rather great danger to any construction, especially if their level is high enough. In this case, you can begin work on the construction of not just any structure, but only one that is able to withstand the negative effects of moisture and carry out the correct distribution of all loads even on such unstable soil. It is mandatory to take measures to drain water and protect the structure from moisture.

A foundation with a high groundwater level must be designed carefully; either a pile type or a special monolithic floating foundation is suitable for construction. It all depends on other construction conditions, the size of the house itself, and the structure of the soil. To determine exactly what conditions are necessary, it is recommended to carry out such work only by a specialist.

Floating foundation

If too high is observed, then only a certain type of base must be used. Usually this is a monolithic foundation. To design a foundation, you must first order a special study, but in some cases you can determine the presence of a problem yourself. To do this, perform the following actions:

Before building the foundation, it is necessary to dig a hole and observe for some time the presence or absence of water in it.

1. To begin with, a hole is dug at the construction site, the depth of which is 3 m, and the side length is 1 m.
2. It is necessary to dig a test hole at the site of the future foundation, otherwise the actions will be ineffective.
3. The condition of the pit should be observed for some time. If it remains dry for a long time, then it means that you can safely begin work on this place. If water appears, the height of which is about 2 m, then this indicates the presence of a high groundwater level. It is recommended to contact a special company to conduct a study, determine the type of foundation, and the features of its structure.

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Materials for work

When the groundwater level is high, special requirements are placed on foundation materials. You can’t save money here, since waterproofing and corrosion protection must be at their best.

Specifically for the construction of a monolithic foundation with a high groundwater level, it is necessary to prepare the following tools and materials:

When building a foundation, a vibrating plate is needed to compact the cushion.

1. Equipment designed for digging a pit. An ordinary shovel is no longer suitable, although it also needs to be prepared. Usually, for foundation pits, they offer construction equipment for rent, which ensures digging of a hole of the required shape and depth in the shortest possible time. When performing such work, you need to remember some rules. The closer the groundwater is to the surface, the lower the height of the slab will be. It is impossible for its lower part to be in the water. This circumstance applies not only to concrete monolithic slabs, but also to blocks.
2. Gravel, sand, which will be needed to fill the bottom.
3. A special vibrating plate, which is necessary for compacting the cushion, especially if the soil is highly saturated with moisture and the groundwater level is high.
4. Polyethylene film for waterproofing. When calculating its quantity, it must be taken into account that it is laid with overlaps; part of the film will extend onto the walls of the pit.
5. Vapor barrier PVC membranes.
6. The choice of insulation must be carefully chosen, since not every material can be used. In this case, when the groundwater level is high, experts recommend using foam plastic boards that are not susceptible to the negative effects of moisture, practically do not absorb water, and do not change their properties even with constant contact with a humid environment. The cost of the material is not too high, and its installation is simple and quick.
7. Concrete mortar for pouring. You can use ingredients for mixing the solution in the form of cement, sand, gravel, water and other things, but experts recommend giving preference to ready-made dry mixtures. Today on sale you can find special formulations designed for high levels of ground water level. This does not mean that additional protection is no longer needed, but such solutions, after pouring and drying, resist aggressive environments much better.
8. To mix the solution, you need to use a concrete mixer; mixing concrete manually is problematic. You can make a concrete mixer yourself or rent it.
9. Special reinforcement and binding wire, which are necessary for reinforcing the foundation.
10. In some cases, it is necessary to use special concrete foundation blocks.

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Base diagram

If groundwater is close, then the foundation design will be slightly different. It is important to immediately determine exactly what type of base will be used. If the groundwater level is high, then the “pie” will be as follows:

1. Compacted soil layer; if necessary, additional work is carried out to strengthen it.
2. A cushion of sand and gravel, each layer is additionally compacted after wetting. The height of this layer is approximately 20-30 cm.
3. Monolithic concrete base, which is reinforced with steel rods.
4. Vapor barrier PVC membrane.
5. A layer of thermal insulation that allows you to create the necessary protection from the negative effects of moisture.
6. A special polyethylene film is used as a waterproofing layer.
7. Screed, i.e. a second layer of concrete pouring, to create the necessary “floating” base. When the soil moves, and this is possible if there is a high groundwater level, all loads will be distributed correctly, and cracks will no longer appear along the walls of the foundation and the house.

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Stages of creation

If the groundwater level is high, then it is best to build a monolithic slab foundation so that it can correctly distribute all the loads from the building. It is necessary to pour such a foundation carefully, strictly following all stages of work:

1. The first step is to dig a pit, the depth of which depends on how close the groundwater lies to the surface. This is determined as a result of a preliminary site survey. It is important to determine in advance the freezing point of the soil, soil structure and other indicators. Digging is carried out using special construction equipment. If water begins to seep through the walls, then it is necessary to take measures for drainage.
2. If groundwater lies close to the soil surface, then measures must be taken to strengthen the walls of the pit.
3. Sand and gravel cushions are placed at the bottom. Each layer is slightly moistened with water and then compacted. If groundwater is too close, a layer of geotextile must be laid at the bottom to protect the entire structure from water. In this case, the sand will not be washed out, the foundation will be well protected from all negative influences. The thickness of the filling, when the groundwater is high, is 20-30 cm. After compaction, each layer is topped up.
4. Pouring concrete can only begin after formwork and reinforcement have been completed. The formwork is made from edged wooden boards, they are fastened with galvanized nails. There should be no gaps left in the walls, otherwise the solution will begin to pour out. At any groundwater level, reinforcement must be provided. For this purpose, metal rods and binding wire are used. The number of belts is usually 2, the grid pitch is calculated individually. This stage cannot be ignored, otherwise the design will not be so reliable.

ElenaRudenkaya (Builderclub expert)

Good afternoon.

I will try to answer all your questions to the maximum. It is very correct that you are trying to delve into and understand all the technology. We work for such people.

1. On the base. That means we didn't understand each other. What is described in this question is true, but for a strip foundation. But it is precisely on the basis of these rules that we recommend that you make a platform from a slab (stand) of 1.5-2 m, since this law also applies to a slab. This is exactly what happened according to calculations. Only not according to the elementary ones, but on the condition that the slab is 30 cm thick and on an unstable solid base, with all the introductory information that you gave us. We don’t publish the calculation itself, but I can write to you briefly what happened:

I calculated the approximate load of the entire house, it turned out to be approximately 200,000 kg, that is, 200 tons. According to the standards, I took 416 kg per m2 load per 1 m2 (this load is according to the standards for unstable foundations). And then I calculated that if your slab is 30 cm thick, then its load bearing area should be approximately 480 m2. You understand that it is impossible to fill such a slab, almost 500 m2, that is, the minimum allowable value of the indentation and the start of construction of the base is 1.5-2 m. This is what I said earlier.

With the same values ​​and inputs, it turned out that if the slab is 1 m thick, then 125 m2 is enough to support it, since your area is a little larger, we give you approximately the normal thickness for the slab, equal to 60 cm, and it is well reinforced. The designer will be able to calculate the reinforcement correctly. In this case, you can start building the base either without retreating at all, or by retreating 10-20 cm.

But I can immediately say that I recently came across a detailed design for a house a little larger than yours and on stable loams, with low GW, but even there 5 tons of reinforcement of different classes from diameter 8 to 28 were laid. Yes, there is a 30 cm slab, but it so reinforced that it’s hard to believe that this even happens. People approached it wisely, checked the geology and they were allowed to make the slab, the designers calculated it. This is a very good foundation in initially good conditions.

2. By filling the site. If you simply level the area and the house will not be placed there, then fill it up, it will compact over time (7-10 years), you can fill it with any soil or construction waste, but not black soil or soaked clays. I'm talking about the corner of the plot.

But in the pit, remember, this is very important. Before construction begins (concrete pouring), you should not touch the foundation pit at all: neither dig nor add sand or crushed stone. This is due to the fact that after the winter your sand will turn into such a dirty, unrecognizable wet substance that any builder will tell you to take it out of the pit and dry it before pouring the foundation. The same thing will happen to the pit itself, the soil will simply become soaked from hot water and snow, the frost will destroy the ground and you will need to dig and clean up this mess again. Therefore, do not touch the foundation pit at all until summer, then lower the hot water level if there is water there and begin work.

3. Regarding the depth of placement. Read the rules here. An insulated blind area is a relatively new invention and you won’t find anything about it in the standards. But we can assure you from experience that it partially retains heat at extremely low temperatures (in Kyiv it can be very cold, down to -30, we ourselves live not far from you and know what it is), accordingly, a warm blind area partially saves you from freezing of the soil. By the way, it allows you to reduce the foundation depth by only 200 mm from the design one. What I do in your case, I allow you to lay the slab at 60 cm, and not at 90 cm; backfilling and drainage are not considered in the design laying depth. I hope I explain clearly.

4. Svarog allowed me to comment on his answers, since we are colleagues and have already discussed everything about your house. Yes, he said that the slab is possible in your case, but this is only subject to geology and good design miscalculation. The shape of the house definitely needs to be changed to rectangular; it is better to insulate the slab from the top (as you write). But you are wrong in one statement: “that the smaller the size of the slab (of the house), the more reliable the foundation will be.” This is not true. He meant that the lighter the house, the more reliable the foundation. Your house is too heavy for such difficult conditions, it needs to be lightened as much as possible. Use frame construction or remove 1st floor. And the risk is precisely that we cannot say exactly what the house will most likely suffer from. It can tilt, crack the foundation (and in this case you know that the entire structure dies), deformations and cracks. Anything can happen. That is why we are concerned about your efforts so that they are not unjustified.

5. On stilts. It's a shame that you think so, but it's your right. There are big doubts about the cost. And if there is a small passage, then in our practice in our region, people manage to screw in piles with a small drilling rig (a drilling machine that digs wells; they are small in size and are transported on trucks). Builders are like that.

6. People have learned to build their houses everywhere, on water, in the desert, and in the snow, but we don’t know how practical this is in your case. You understand that slab foundations and pile foundations are specialized foundations. They are built in cases where conventional types of foundations are not suitable, and in most cases for special-purpose objects, but not a private house. This is a forced measure that is expensive and unjustified. The fact is that this flooded area may manifest itself unpredictably in the future. The level of HS has recently (over the last 17-20 years) increased very strongly throughout the former USSR. People are tormented and constantly write to us about what to do with a house that has existed for 50 years and has never seen water. And you initially want to build on water. Your swamp is not drained, it really exists, but so far only in a dormant state with a slight rise in the water level. I am in no way trying to persuade you or scare you, I am only warning you. All my colleagues agreed on one opinion: it is not worth building on water. But this is our opinion, you don’t have to listen to us.

7. According to the brand of concrete. You also have aggressive waters, and it’s good that at least someone is doing geology. Even if this geology is neighboring, it makes it clear that you have an aggressive environment with sulfate activity. Sulfate resistance of concrete is its ability to withstand the overly aggressive and extremely destructive effects of liquid sulfate media for a long time. The molecular volume of ettringite increases the existing volume of the initial phases. This causes small microscopic cracks to appear in the concrete, which then become large cracks. Sulfate-resistant concrete is resistant to this kind of influence. Such concrete is not used often and its price differs from the price of ordinary concrete (more expensive).

• Sulfate-resistant concrete is obtained from the most common average cement, but only when mixing this mixture are special modifying additives intended for concrete added to it.
• In addition to additives, you can use types of sulfate-resistant cement specially designed for this purpose when mixing concrete.
• Substances such as superplasticizers, plasticizers and air-entraining additives help to significantly and significantly increase the sulfate resistance of concrete.

That is, you need moisture-resistant concrete of grade W6 with modifying additives. Hence the conclusion that making a 60 cm slab will be very expensive.

Your geology is necessary to find out if there are quicksands or any other surprises, since you correctly say that even in one area you have different soils, they can be different even by 1 m2.

Ask.

answer

The main task of the foundation is to take the load from the house and distribute it evenly onto the ground. Therefore, when laying the foundation, it is necessary to take into account the type of soil and the location of the groundwater level (GWL). The last indicator may be too high, that is, the water is close to the soil surface.

Pouring a foundation under such conditions is difficult and costly. Therefore, the work contractor is faced with the question of what kind of foundation is needed for a private house if groundwater is close? This question affects not only the type of foundation structure, but also an additional choice that concerns the laying depth: below the groundwater level or above.

Groundwater influence

In the construction environment there is such a term - cement bacillus. This is when a concrete structure is destroyed under the influence of negative factors, which include groundwater. But we must understand that it is not the water itself that negatively affects concrete, but the salts and various chemicals dissolved in it. They penetrate into the concrete body, where they interact with cement or fillers, breaking their bonds with each other. Hence the appearance of all kinds of plaque, dark spots and unpleasant odors.

High groundwater level is a problem even at the stage of digging a pit. Water collects inside, which softens the bottom, which leads to a decrease in the bearing capacity of the soil. If this happens, you will first have to think through and install a drainage system, with the help of which it will be possible to pump out the water.

There are technologies that do not require drying the site. To lay the foundation, a pile method is used with driving pillars into the depths of the earth to dense layers. Not a bad option, but expensive and time-consuming. Without special equipment, such a foundation cannot be built. For private housing construction, this technology is rarely used. Therefore, the construction of a foundation with a high groundwater level is approached from the perspective of drainage.

And one more negative point. The dangerous time for such areas is winter with sub-zero temperatures. Freezing of the soil in winter turns into a dangerous situation for the foundation. Frost heaving and high groundwater level can destroy the foundation structure of a house in one season.

Determining the level

The groundwater level, that is, the indicator itself, is recorded in a geological organization, which has a branch in any large city. You can get information on the State Regulations there. Or you can measure the level yourself. To do this, you will have to dig a hole 3 m deep. Or drill a well to the same depth. A hole diameter of 20 cm will be normal, which will only require a garden drill.

Measurements should be taken in the spring, when the snow has melted. This is the period when the groundwater level is at its maximum peak point. Cover the hole with film to prevent precipitation from getting into it. And after a day you check how much water has accumulated in it. You can check with a pole: lower it all the way so that it touches the bottom. We pulled out and measured the dry area from the wet one to the mark that determines the ground level (the mark must be placed when measuring in the hole). This is the UGV.

1. If this indicator is more than 2 m, it means that in the area where the house is being built there is a moderate groundwater level. The foundation can be laid without additional measures.
2. If the length of the dry section is less than 2 m, then the water level is high. We will have to think through a water drainage system, construct it, and provide the foundation structure with protective materials.
3. It is the second position - with high groundwater - that will require the work manufacturer to select the type of foundation.

Soil freezing depth and groundwater level

The presence of high groundwater flow affects several positions related to foundation laying. They are clearly stated in SNiPs. And most often in the rules there is a correlation between groundwater level and the level of soil freezing. Because these two indicators are the main factors that reduce the strength of a concrete structure. Here are a few positions.

1. If the water level is less than the freezing level, then the foundation is calculated according to the usual scheme, that is, only for the load from the house.
2. If the soil at the construction site is weak, soft and mobile, then the foundation is laid below the UPG. In this case, a drainage system must be organized to drain groundwater.
3. If the groundwater level is very high, then it is not recommended to build a strip foundation.
4. If there is frequent flooding in the building area, then the only acceptable option is a house on stilts. In this case, the pillars are driven into the ground below its freezing level.

If the groundwater level is high enough and the area is drained, then there is a high probability of soil subsidence. This especially happens on sandy soils.

GWL closer than 0.5 m

In this situation, the only solution is piles. There are three options: ready-made monolithic, screw made from steel pipe and bored.

1. The ideal option is monolithic. They have been used in construction for a long time; they have increased load-bearing capacity and can easily withstand frost heaving. In addition, there is no need to think about soil drainage. True, this will require special equipment.
2. have become very popular today. In small private housing construction, such foundations for high groundwater are the optimal and cheap solution. Their only drawback is not the highest load-bearing capacity. Therefore, you will have to calculate the number of piles and the distance between them. It is recommended to install screw piles to a depth of no more than 3 m.
3. As for bored structures, this is a good option that has a high load-bearing capacity. But this technology also has its drawback - a large amount of drainage measures will have to be carried out.

From 0.5 m or more

When choosing the type of foundation, preference should be given to the slab model. The thing is, if we are talking about a house, columnar structures in such a situation will not be able to provide the necessary load-bearing capacity of a large structure.

You can use it, but only a shallow one, which is usually built for small, lightweight buildings. In principle, it will withstand a frame cottage. In this case, it is recommended to build a foundation with an expanded base.

On the subject: When pouring it to a depth of up to half a meter, you need to understand that its thickness and method of reinforcement will depend on the number of floors of the building, as well as on the type of materials from which the walls will mainly be built. In this case, you will have to think about thermal insulation technology. By the way, this is an important stage in the construction of the slab.

Replacing the soil will help increase the load-bearing capacity of the slab. It is taken out to the groundwater level and instead filled with sand or crushed stone with careful compaction.

If the soil on the site is very weak, then the houses are filled with high groundwater until its materials displace excess moisture and stop sinking deeper.

1.5 m or more

Comparing the conditions described above, it should be noted that in this case it is possible to use strip and slab foundations on groundwater. But both structures must be shallow-depth.

Options for close proximity to groundwater

Options for foundations with close groundwater have already been given above. In principle, the slab structure in this case is the most commonly used structure. There is no need to build drainage ditches or think through protection methods, because everything is carried out using standard technology.

High groundwater - building a house without a basement

Everything here is quite simple if you use a surface or shallow slab as a base. That is, a house is being built without a basement and the walls rise immediately from the slab. Here is the sequence of work carried out:

1. A pit is dug up to the groundwater level;
2. A cushion of sand and crushed stone is filled with a tamper;
3. Waterproofing with roll material;
4. Installation of reinforced frame;
5. Pouring concrete.

If an insulated base is being constructed, then insulation is placed under the frame. In areas with high levels of subsoil water, this is an ideal foundation option.

Protection from high groundwater level

In the construction of foundations on such soils, three types are used, with the help of which it is necessary to protect the structure of the foundation and the house itself.

1. Coating, when bitumen mastics are applied to the foundation itself in several layers, due to which a smooth waterproof layer is formed on the surface of the structure.
2. Rolled, when the structure is covered with waterproofing films or membranes in several layers.
3. Plastering, when cement mixtures containing waterproofing additives are applied.

The thickness of the waterproofing layer is determined based on the occurrence of groundwater. The higher their level, the thicker the insulating coating.

Construction of a foundation on a floating cushion

What is a floating pillow? This is a thick layer of base made of several materials, which are separated from each other by insulating films. For high groundwater it is done very often. Here's the sequence:

• Coarse sand is poured into the bottom of the pit or trench and compacted well.
• Backfilling is done in layers with compaction of each layer. In this case, the final result is a layer 50 cm thick.
• A waterproofing film is laid, preferably roofing felt.
• Crushed stone is poured and compacted to a thickness of 30 cm.
• Another layer of roll waterproofing.
• Filling the screed with a thickness of 10 cm.

After which you can pour the monolithic reinforced concrete structure of the foundation itself. The pillow creates conditions under which the foundation can move relative to it. Such a foundation is often called a floating monolithic foundation.

Tape

The strip foundation on soils with high groundwater level is poured in exactly the same way as described in the previous sections. It is important to understand here that a strong base in the form of a tape is a large material cost. They mainly concern the consumption of concrete and reinforcement. At the same time, they try to construct the tape itself with an expanded sole.

If you try to save on something, the end result can lead to a weakening of the foundation structure, and, consequently, problems with the house itself will begin to arise. Therefore, one cannot deviate from the construction technology and the exact sequence of construction operations.

Pile type

As already mentioned, a pile foundation with a high groundwater level is the optimal solution. The main thing is to choose the right type of elements to be installed.

As practice shows, when constructing a large, heavy house, monolithic reinforced concrete pillars are used, which are manufactured at reinforced concrete factories.

This technology is called TISE. It’s true that this is not the cheapest technology of all piles, but it is the most reliable.

And although a screw foundation is cheaper, it does not provide the necessary load-bearing capacity for a heavy structure. It must be taken into account that waterproofing in a screw pile or other type of device is a mandatory measure.

Conclusion on the topic

So, the question of what kind of foundation to make if groundwater is close is very relevant today for many private developers. The article examined almost all the situations that they may encounter, and also recommended the types of foundation structures. In fact, it is important to understand that the choice itself is based not only on the types of soils and groundwater level.

It is important to first understand what kind of house will be built in an area with such a soil situation. If you are planning a large building made of bricks or blocks, you will have to allocate a decent budget for its construction. And you can’t save money here, because high groundwater level means moving, unstable layers that have weak bearing capacity.

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