What foundation if clay. Building a foundation on clay
The construction of a foundation on clay soils is often associated with a number of difficulties, and the greatest difficulty is the combination of clay soil and closely spaced groundwater. Wet clays belong to the V group of soils according to the deformation of frost heaving; when frozen, they are capable of exerting tremendous pressure on the sole and foundation walls. If the building is improperly designed, then cracks, dips and destruction of the house may occur. Therefore, when constructing a capital structure on clay soils, it is imperative to contact the design organization. If it comes about building a foundation on clay for small house, bathhouse or garage, you can perform it yourself, taking into account the recommendations given in the article.
The choice of the type of foundation for clay soil
First of all, it is necessary to determine several features of the soil on your site:
- The content of clay particles in the soil;
- Soil moisture;
- Freezing depth for your region;
- Ground water level.
The composition of the soil is determined as follows: you need to take a certain amount of soil in your hand, knead it and try to roll up the "sausage". From the sand this will not work at all. Loams acquire the necessary shape, but soon crack and break up into separate pieces. If the whole plastic “sausage” is obtained from the soil - this is clay, one of the most difficult for the construction of soils. To determine the humidity, it is necessary to leave the soil for some time in the air. If the drying lasts several hours, then the soil is moist. It is these soils that are most susceptible to frost heaving.
The groundwater level at the site can be determined by a well or by drilling a pit. The depth of freezing of the soil is determined by reference data, for this you can use the table:
If the groundwater level is much lower than the depth of soil freezing, then you can erect a shallow. At the same time, the sole of the foundation is recommended to be wider than its upper part, in order to increase the area and reduce the specific load on the soil side. Under the sole of the foundation, it is imperative to erect a thick sand cushion - it will serve as a kind of shock absorber, and also allow you to remove excess moisture from the foundation. In this case, the foundation must be waterproofed from the outside with rolled materials with high strength - this will prevent clay from sticking to the foundation and shifting a large mass of soil together with the foundation when it freezes. Also, it will not be superfluous to warm the soil around the foundation by creating a blind area. It must be borne in mind: if the project is carried out with the expectation of heating the basement, you can not freeze it - this can lead to serious deformations.
With a close location of groundwater, a device with a deepening of piles to a considerable depth is necessary. In the lower part of the piles, it will be necessary to perform an expansion that will not allow the forces of frost heaving to push the foundation out of the ground.
Recently, the technology of steel screw piles is gaining more and more popularity. Screw piles are a hollow metal pipe with a pointed end on which the blades are located. When screwing the piles, these blades are drilled into the ground, which contributes to the advancement of the piles inland. Pile blades do not loosen the soil, unlike concrete piles, so the soil around the screw steel piles retains the initial compaction.
Clay foundation technology using screw piles
- Site preparation is reduced to geodetic exploration, calculation of the required number of piles and the approximate depth of their installation. Screw piles can be installed at different depths, which is convenient for areas with a strong slope or uneven soil type. Piles must be installed in the corners, as well as at the intersection of the walls. In addition, piles must be placed along the bearing walls at a distance of at least 2 meters. After calculating the number of piles according to the drawing, the specific load of the building for each pile is checked, if necessary, determine the installation location of additional piles. The site is cleaned of construction debris and foreign objects. Soil over the entire area of \u200b\u200bthe building is cut off. Make markings, marking the installation site of piles.
- Screw the first corner pile. This can be done either manually, using a lever, or using a special mechanism. Clay soils are quite heavy, so it is better to choose the second option. When screwing the piles manually, you must always check its verticality on the slope. The slightest deviation can cause the building to skew during operation.
- Subsequent piles are screwed in the same way. In this case, it is necessary to check from time to time with the layout plan of the piles. Screwing up the piles is carried out until they reach the calculated depth, that is, below the depth of freezing of the soil and the level of groundwater. If the depth of the pile is not enough, produce its buildup.
- After screwing all the piles on the hydraulic level, mark the floor level of the first floor. As a rule, it should not be lower than 50 cm for residential buildings and 30 cm for a gazebo or outbuildings. All piles are marked at this level and the excess length is cut off by the grinder.
- Piles to give them greater strength are filled with concrete of grade no lower than M200. With a significant depth of piles, it must be sealed with a reinforcing bar during pouring, piercing the thickness of concrete with it. When constructing a temporary structure from light materials, piles can not be poured, and then reused.
- For horizontal stability, the piles are tied with a beam or channel. The channel is usually used for brick or foam concrete walls, timber - for houses made of timber, logs or frame structures. For tying the beam, it is necessary to put on the pile a head with holes for securing the beam. The channel is fixed by welding.
The process of tying screw piles with a beam for stability
The foundation of screw piles can be installed even in frozen ground, which is convenient for areas standing on the floaters. Due to its high productivity and short lead times, this technology has become widespread, especially in the construction of houses from profiled timber or frame structures, for the popular canadian technology. Pile buildings can be installed on steep slopes and on the banks of ponds by attaching piers. Also on piles, arbors, terraces and other elements of landscape design are often installed.
If the construction site is located on clay soil, it is necessary to familiarize yourself with the nuances of the ground masses with their characteristics. For this, a preliminary analysis of the soil, its bearing capacity, the depth of the aquifer, the freezing point, etc. is carried out. But it is worth considering the types of clay soil, so that the construction of the foundation of the house does not cost too much.
Soil types
To determine the “clay” in the soil should be at least 30% of this material, loam is 10% clay, and sandy loam contains 5-10% clay. There are types of clay glacial and alluvial. Glacial is characterized by a very high density and excellent bearing capacity, revealed only in the deep layers. Alluvial clay is a plastic soil, so it is better to completely abandon construction work on such a site or equip the structure on stilts.
The nuances of foundation technology, types of foundations
When starting the construction of the foundation of a house on clay, it is important to remember that the soil does not tolerate water, therefore it is important to conduct geological surveys. For example, maybe in your case clay layers alternate with sand layers, and you will have to take into account the depth of each layer. Performing the work yourself, you can determine this fact by digging pits, the depth of which depends on what depth will be the type of foundation being built.
Important! While maintaining the heterogeneity of the soil, it is better to use crushed stone or sand filling, given the moisture of the layers. And with a high elevation of groundwater, it is better to give preference to a pile foundation.
Shallow basement on clay soils
The design makes you think because of the low bearing capacity and low strength of clay soil. To avoid the danger of cracking and skewing the foundation of the house, it is better to use a reinforced concrete plate, ideal for this type of soil composition.
A floating foundation is also allowed, the strength of which does not depend on the intensity of soil erosion. The slab is poured on its own using concrete of particularly strong grades. But you can take the finished plate, additionally reinforced. The depth of the bookmark will depend on the weight of the house. And for the installation of the slab you will need a foundation pit with a pillow of gravel and sand.
Advice! The high cost of the project is considered a disadvantage in arranging such a foundation.
Strip foundation
Only a recessed strip foundation is permissible. Construction begins with digging a trench deeper than the freezing point. Then the bottom is covered with gravel, sand and it is important to take into account the depth of the trench in order to equip the correct thickness of the pillow. After that, on top of the sand, a layer of insulating material (polyethylene) is lined, which ensures a decrease in the pressure force of the weight of the house on the foundation on clay soil. At arrangement tape basebefore pouring into the trench concrete composition, it is necessary to mount the fittings connected among themselves.
Advice! The arrangement of the tape base is justified in cases where it is necessary to have a basement of a house being built on heterogeneous soils. And if the construction is carried out on heaving soils, it is worth giving preference to the foundation on a monolithic slab or piles.
Advantages of the tape base on clay:
- The possibility of arranging a basement or basement;
- High structural strength;
- Long service life without loss of quality characteristics;
- Providing a solid foundation for the structure.
- High cost of work;
- The need for the consumption of a large amount of material;
- Labor input.
Clay pile foundation
This type of foundation is considered particularly popular due to the provision of sufficient strength and stability of the entire structure. Moreover, the type of pile supports is large, which allows you to choose the most suitable elements for homogeneous clay and heterogeneous soils.
Important! When deepening piles, it is necessary to achieve dense layers that do not undergo freezing, displacement due to filling with aquifers. The immobility of these layers will protect the base, and, consequently, the structure, from all destructive factors.
Experts recommend the construction of a pile foundation on clay using driven or screw piles, choosing which type will cost more economically and more practical. But in some cases, bored piles for a house are permissible, the installation of which requires drilling holes, pumping out water, reinforcing and concreting. At higher costs, this method guarantees exceptional base strength.
Pile foundation advantages:
- Increased durability over the long term;
- Withstand large weight loads;
- Ideal for unstable ground masses.
Disadvantages:
- Threat of susceptibility to corrosion (treatment of piles with special compounds will help minimize the threat);
- The need for additional costs;
- The lack of a basement, or the obligatory implementation of laborious and costly work.
Clay base on clay
If you plan to build wooden house without a basement on clay, this option is better than any other. Therefore, choosing which foundation will be, it is worth paying attention to the least costly way of arranging the foundation. The technology is simple, you need to dig columns with a pitch of at least 1 meter, and the base can be from pre-burnt piles made of oak or pine wood. The holes for piles cannot be higher than the freezing point of the soil, but should fall below at least 2 meters.
The advantages of columnar bases:
- Affordable price;
- Efficiency of installation and the ability to do it yourself;
- The use of small quantities and assortment of materials.
- Short term of operation;
- Low bearing capacity, for buildings of large mass it is better to choose a different base;
- Do not use on moving soils.
Given all the features, you can always choose which foundation is more suitable for arranging on a construction site for strength, efficiency and speed of construction. However, considering precisely these factors, one can not ignore the mass of the structure, the water content of the soil, the number of storeys of the building and other characteristics that affect the operation and durability of the house.
Clay foundation, which is better to use? Such a question arises before the builder when it is discovered that there is clay soil in his area. The strength of the foundation depends not only on the quality of building materials. The reliability of the building is greatly influenced by the characteristics of the soil on which the house rests.
Therefore, it is extremely important at the design stage to choose the best option for the foundation, corresponding to the geological structure of the building site. This article will help private builders who are going to build a house on clay: which better fit for such a case?
The main problems in the construction of a foundation on clay soils is the likelihood of subsidence, breaking and swelling of the base of the building. This can happen under the influence of too much pressure on the foundation, or due to insufficient depth of its laying.
In the high-risk zone are houses, the walls of which are built from light building materials - foam blocks, for example (). The heaving forces in clays can be balanced only by the heavy above-ground part - brick, stone or reinforced concrete.
Types of clay soils
Clay soils include:
- sandy loam;
- loam;
- clay.
Clay is a combination of small (up to 0.01 mm) particles with a small admixture of sand and dust. It is characterized by flowability and high ductility. It is possible to build on clay if the soil is homogeneous, and groundwater lies deep. But in any case, such a case is not at all suitable for independent construction.
Loam contains up to 10% clay. Depending on its specific volume, the soil can be light, medium and heavy. Loams are prone to frost heaving, so the construction conditions on them are difficult.
Sandy loam contains no more than 5 percent clay. These soils have another name - quicksand, as they have great mobility under the influence of groundwater. To build a foundation on sandy loamy soils is undesirable, but if there is no other way, choose pile structures with crushed stone base.
Choosing the type of foundation
When building a foundation on clay soil, regardless of the type chosen, the main rule must be followed: the sole width should be 25 percent or more greater than the top of the structure (). A pillow made of sand and gravel (or gravel) is mandatory.
Strip foundation
Clay strip foundation is suitable for heavy buildings and light wooden structures ().
But if in the first case a recessed structure is set up, the sole of which is below the freezing boundary, then in the second case, a shallow foundation should be preferred: on clay soil, the light above-ground part cannot counterbalance the heaving forces.
Monolithic tape is used only if the groundwater is below the freezing line of the soil. A foundation of this type can be built on loamy soils if geological exploration has confirmed the uniformity of bedding throughout the construction site.
Only in this case, uneven deformations during heaving of the soil will not threaten the structure.
Slab foundation
Clay foundations on clay are the most reliable, but also the most expensive). Therefore, they are practiced only in the case of the construction of luxury mansions.
Another name for this type of foundation on clay soil is floating. With any movement of the soil, the slab moves with it, while maintaining a uniform load.
The plate is poured almost on the surface of the earth. But they also practice buried slabs - in houses with basements. In this case, the walls of the underground part of the house, and the stove make up a single monolithic structure.
If you need to build a foundation on loam, you cannot find a better solution than a monolithic slab (). Since the sole of such a base has a maximum area, even a design soil resistance of 1 kg / cm2 is sufficient to ensure the stability of the structure.
Pile foundations
With the help of piles, a foundation is built on sandy loam and other types of clay soils. Pile fields are arranged under the buildings of a large area: under the walls, the supports are installed in rows, and under the columns - bushes.
When choosing the type of foundation on clay soil with a high level of groundwater, the most appropriate solution is to build a house on stilts (). In this case, it is necessary to adhere to the basic rule - the support should be performed with broadening downward.
Well established screw piles - constructions equipped with screw blades in their lower part). When the screw is screwed in, the density of the soil around the support is maintained - the blades do not loosen the soil, but separate layers are cut. The estimated screw installation depth is below the aquifer and the freezing point.
Scheme of pile - screw foundation on clay soil.
Conclusion
The installation of the foundation on clay soils is a complicated, but quite feasible business. The main thing is to know all the advantages and disadvantages of such soils and correctly use the first, avoiding the second.
Video about how clay is dangerous for the foundation.
The house begins with the foundation. The life of the building and the safety of the inhabitants of the house depend on its quality. In order for the foundation of the house to be reliable, it is necessary to acquire quality construction Materials, find out the composition of the soil, get acquainted with existing species foundations; find out which foundation is best used on clay.
It is not so easy to build a foundation on clay soil, therefore, it is necessary to prepare especially carefully for this process. Clay undergoes a compression process under the influence of building mass pressure. This can go on for more than one year, and during all this time the building gives sediment, which can lead to deformation of the foundation and damage to the building. There are other “capricious" properties of clay that adversely affect the results of construction.
Types and features of clayey soil
There are several reasons for the classification of soil in science. In one of them, the proportion of the presence of certain particles in it is taken as a basis. In nature, it does not happen that the soil consisted only of clay or only sand, or only any other rock. There is always an admixture.
In this regard, several types of clay soil are distinguished.
- Clay. This type of soil contains at least 30% pure clay. To determine its amount in the soil composition, you can use this method - to roll a “sausage” from clay, if after some time it does not lose ductility, then the percentage of clay content can be considered high. When building a foundation on this type of soil, it is very important to know the freezing point, it should be higher than the groundwater level.
- Loam. The clay content is between 10 and 30%. A lump or “sausage” made of loam remains plastic only for a short time, then it dries and breaks up into small particles. In turn, according to the quantitative presence of clay, this type of soil is also divided into types - light, medium and heavy.
- Sandy loam. The clay contained in the composition is between 5-10 percent. Plots with this type of soil are very susceptible to groundwater.
When constructing a foundation on clay soil, it is imperative to consider which of its types lies on the territory of construction work.
Given the characteristics of clay rocks, you need to know that the clay itself, which is in their composition, is not only different in color (red, white, blue, gray, etc.), but also has very different properties. For example, glacial clay can withstand high loads only if it lies in a large layer. With its surface location, the soil is easily washed out by groundwater and meltwater.
Layers of alluvial clay lie near water bodies in lowlands. She is very plastic. Experts do not recommend building on sites with a similar type of soil. In case of emergency, you need to more carefully approach the choice of the foundation for the construction.
How to choose a foundation
The construction of the foundation on clay begins with geological exploration, during which the type of soil, the methods of its occurrence are determined. It is important to identify the presence of groundwater and their location relative to the surface. It is necessary to establish to what depth the soil freezes. All these factors are decisive in the matter of choosing the foundation for the future building. The dimensions of the building, the material for the laying of the walls also must be taken into account during the preparatory measures.
The consideration of the project of a shallow foundation for a large building on clay soil must be approached with particular care. The strip foundation made in this way should be immediately excluded.
One of the acceptable options is a floating foundation, which is a monolithic reinforced reinforced concrete slab. It can be finished or flooded on its own. Possible shifts of clay layers to such a foundation can not do harm, and, therefore, the whole building will be safe. The level of deepening of the foundation slab depends on the size of the building being built. The main "drawback" of the project is its high cost.
On clay soil pile foundation erected when groundwater is located close to the surface. This option base in this case will be optimal. Piles are driven in or screwed in (in the case of steel structures with blades) to a depth where solid fixed ground rocks lie, thereby ensuring the reliability of the structure. It is very important to correctly calculate the number of piles, their location under the building, size. Piling can be done manually or mechanically. The column or pile foundation is not used in the construction of the building, where the project provides for a basement.
“Tape” is another version of the foundation of a building for clay soil. But it must be remembered that the depth of the foundation on the clay in this case is very important. It can not be less than the depth of freezing of the soil. Thus, it is necessary to take into account one more factor when choosing the type of foundation - the climatic conditions under which construction is underway. It is only clear that the strip foundation for the building being erected on clay soil should be buried.
Sometimes a combination of different types of foundation is possible. For example, a slab is laid under the main building, and for those places where there is no heavy load (terraces, stairs, porches), a strip foundation is laid.
To answer the question, which foundation is better to use on clay, you need to consider a lot of factors, so the question of choosing the foundation for the construction is decided individually. It will be very useful to consult with professional builders or people who have rich experience in such work before starting construction.
The strength of the foundation on clay largely depends on what methods and techniques builders use. There are some tips to help you avoid common mistakes.
- When laying the foundation, it is not recommended to save money that goes on the purchase of building materials. It requires the highest quality modern materials.
- The bottom of the finished pit or trench must be cleaned up in one of the ways - manual or mechanical. Manual bottom leveling is done with a shovel, and mechanical leveling is done with a mini excavator with a leveling bucket mounted on it. At this stage, the use of a laser level is mandatory.
- At the bottom of the pit, under the foundation, be sure to lay a “pillow” consisting of crushed stone, gravel and sand. Sometimes low-quality concrete is used. This is done in order to horizontally level the bottom surface, to ensure depreciation of the foundation.
- To reduce the pressure of the soil on the foundation and ensure its waterproofing, two layers of plastic film, roofing felt or other waterproofing material are laid on the bottom and walls of the trench.
- To give the foundation greater stability, the foundation is made wider than its upper part by about 25-30%.
- When pouring the strip foundation with concrete, be sure to lay the connected reinforcement in the trench. Reinforcement in the foundation slab is made with two layers of mesh.
- The depth of the trench should not be less than the thickness of the fertile layer of the earth, it is necessary to deepen from it by at least 50 cm.
- In the finished trench, formwork is performed from wood, sheet iron, laminated plywood or other material. After pouring and drying the mixture, the formwork structure is dismantled.
- The reinforced concrete mixture poured into the formwork is rammed (by vibration) to remove air bubbles and improve the properties of concrete.
- When erecting a foundation on clay, drainage and insulation work are not excluded.
- You can find out such an important indicator as the depth of soil freezing for different regions of Russia in a special summary table, which is available in the architectural department of any city, it is published in specialized literature, on Internet sites, etc.
The foundation will become a reliable foundation for the entire building only if it is erected taking into account all the details and observing the technological processes.
The foundation of any structure is the foundation that determines the life of the construction site. The cost of arranging the foundation is one third of the total estimated costs and it is not practical to save on it. Far from always high-quality building materials guarantee strength. Equally important is the surface on which the construction is carried out. The foundation on clay soil is fundamentally different from the filling of the base in chernozem areas.
Building a solid foundation on a heaving basis is a serious task. After all, it can behave unpredictably, which is associated with the ability to retain moisture, push the building. Insidious clay is easily washed away by water, loses its integrity, opens up access to moisture to the elements of the constructed building.
Before building on problem soil, study its properties, determine the type of structure. The price of error is high. These are cracks, failures and possible destruction of the building. Building capital facility in clay soils requires assistance design organizations. If you plan to erect an outbuilding, bathhouse or premises for vehicle, then you can cope with this task yourself by studying the recommendations indicated in the article.
The main feature of clay is the ability to quickly erode under the influence of water, without passing it deep into it
Preparatory Activities
If there is no choice and you have to build a foundation on clay soil, pay special attention to the following points:
- the type of clay-containing soil, which is determined during prospecting work involving drilling, sampling at a future depth of the base. Perform geological exploration in the spring, when the groundwater level is maximum, which allows for detailed studies;
- the level of soil freezing for your area, which is determined for a specific region using the reference information;
- moisture concentration. Humidity can be determined by leaving the sample to dry in the open. If the process takes several hours, then this indicates increased humidity, causing swelling;
- the depth of aquifers located in the upper layers of the soil. Having drilled a pit and, guided by a nearby well, you will assess the level of location of aquifers.
Let us dwell in detail on the types of clay soils.
Clay soils are called heaving, and before starting construction it is strongly recommended that studies of the composition and uniformity of soils in the area
Varieties of clay soil
For clay soils, a characteristic feature of the structure is the presence of microscopic plates, in the gap between which moisture is concentrated and retained. This nuance causes the tendency of the soil to significantly increase in volume at freezing temperatures, when frozen water swells the massif and gradually displaces the base of the building.
You can try to knead the soil yourself. Of the loamy fractions, the “sausage” is cracked, and the plastic mass indicates that you have clay that is difficult to build.
In different regions, the soil is different. Before performing a foundation on clay soil, determine what soil is on your site: