The columnar foundation is considered one of the simplest and cheapest to perform. Such a foundation has been used by builders all over the world for a long time. Its installation does not take much time, and it can also be used in deeply freezing and heaving soil. Also, if there is a grillage, it can be used on unstable soil..
- Advantages and disadvantages
- Types of foundation posts
- What is soil heave and how does it affect the choice of foundation
- Application area
- Depth of laying
- Foundation construction rules
- Construction stages
This design consists of supports that are installed in places of greatest stress. Most often these are the corners of buildings, load-bearing elements, columns, stoves and other components of buildings. It is well suited for frame buildings, as well as houses made of aerated concrete, SIP panels, and other lightweight materials..
The parts are installed at a distance of 150-250 cm from each other. In some cases, a greater distance is allowed, but for this you need a powerful monolithic grillage. Most often it is used for construction:
light buildings without a basement;
buildings that require a low draft;
brick houses, for which it is unprofitable to establish a solid base;
buildings on soils with strong heaving.
The arrangement of foundation pillars implies a minimum cross-section of elements, which depends on the material of manufacture and is:
concrete – 40 cm;
stone – 60 cm;
brick – 38 cm;
brick with a filling – 25 cm;
rubble stone – 40 cm.
Advantages and disadvantages
The widespread use of this type of base is due to its advantages over other varieties. Among them, the following stand out:
reliability even with a high degree of heaving of the soil and the close location of groundwater;
long service life;
do not require expensive waterproofing;
leveling the soil is not necessary.
However, like any other structure, the foundation on the pillars has its drawbacks. The owners of such houses and builders note:
problematic construction of a basement and basement;
horizontal movement of the soil can destroy the structure, therefore, a high-quality grillage is important;
Any builder will confirm that there is no perfect foundation, so a choice must be made based on the specifics of the project and the type of terrain. You also need to think over all the required costs and your skills in construction..
Types of foundation posts
In practice, various types of poles are used. According to the material used, they are divided into concrete, rubble concrete, brick, stone and wood. There is also a classification by depth, in which shallow and buried are distinguished. The former are deepened 50-70 cm underground and are usually used on rocky or sandy soil with a low groundwater level. The second variety is suitable for wet areas. They are installed 50 cm deeper than the freezing level. In order to properly carry out the installation, it is necessary to carry out geological surveys.They fall into the following categories depending on their design:
monolithic – is a homogeneous product characterized by high strength and durability;
made of metal or asbestos pipes – it is quite simple to install, due to which it has become widespread. However, it requires high-quality waterproofing, as steel corrodes;
prefabricated from sand blocks that are installed on sand cushions. All components are fixed to cement mortar;
with a grillage, it is able to evenly distribute the weight of the building and absorbs horizontal vibrations. This component is intended for combining pillars.
For a columnar base, durable raw materials are used that are able to cope with loads and are resistant to environmental influences. Most often used for these purposes:
concrete grades B15-B25;
metal, asbestos and other pipes, into which reinforcement is inserted and poured with concrete;
Depth of laying
Depending on the structure of the base and the building itself, as well as the conditions of the area, the degree of deepening is selected. As mentioned above, buried varieties are distinguished, which are lowered below the level of freezing of the earth. When they are shallow, they are dug in at 40-70 cm.Also, sometimes they are used not buried, which are not buried at all in the ground. Regardless of the type of pillars, before installing them, it is necessary to remove the fertile soil layer. Otherwise, in the process of rotting grass and other components, the product will shrink and may collapse or crack..
This type is a lightweight version of the base. It is suitable for the construction of sheds, gazebos and other light buildings. It consists of several pieces of concrete, laid on a layer of sand and gravel. Supports in this case are placed at the corners of the building and in places of greatest stress. To increase the bearing capacity of the soil, it is necessary to carefully tamp the pad. If you have loose or water-saturated clay types on your site, it is not recommended to use this variety. Since even a light utility room in this case will be unstable.
What is the difference between this type and a pile foundation
At first glance, these designs are very similar and many people do not even notice the differences. However, they are also very significant. Piles are installed on soft soils to a greater depth in order to transfer the load level to stronger layers. The pillars are used for normal lands and deepen a relatively short distance. In addition, the first type is installed using special technology, while the installation of the second is possible with a minimum set of tools. In general, they do have similarities, but they have completely different areas of application. Therefore, they are classified as different types.
What is soil heave and how does it affect the choice of foundation
This phenomenon is inherent mainly in clayey soil types, which are quite difficult to build. They are always very wet, as they do not allow water to pass through well and it accumulates in cavities. When the liquid freezes, it expands, thereby increasing the volume of the soil, as a result, it swells. These forces act on the support from all sides. The pressure from below tries to push it out, and from the sides – to move it to the side. As a result, low-quality material deforms or even breaks. Because of this, it is recommended to make reinforced monolithic pillars in the heaving earth..
To protect against upward impact, the lower part, called the heel, is extended. It is best to make it 2 times thicker. The height of the enlarged area should be one third of the entire length. Seams between prefabricated components are the most fragile places. Therefore, the supports are made with beveled walls. This allows you to better resist heaving. If you have normal soil on the site, you do not need to make a bevel. To reduce the impact of ground movement, take the following measures:
at the very bottom they equip a gravel cushion, which takes on some of the loads;
smooth side surfaces lubricated with grease, do not allow the column to move;
an insulated blind area is being erected around the house.
Pillar foundations are ideal for light structures on normal ground. It is not used for loose soils, peat bogs and other unstable sites. Due to the design features, you are unlikely to be able to make a basement.
Most often, pillars are used for light houses, and with a large deepening, they are able to withstand heavy walls. In addition, such a base is ideal for heaving soils, since less forces act on it than on tape and other varieties. It is highly discouraged to choose the installation of a columnar foundation in the following cases:
if there is a large elevation difference on your site;
with the likelihood of reservoir displacement.
Depth of laying
Before making supports, careful calculations must be made. Usually, to ensure stability to changing factors, all parameters are taken with a margin. So the depth of entry into the ground is usually taken more than required, because over time conditions can change.
This is especially true for heaving soils, where it is difficult to perform accurate load calculations and therefore it is necessary to make the most reliable elements in advance. If your site has a high clay content, you should lay the pillars below the freezing level. To do this, you need to find out the average data for your region and add about 20 cm to provide the necessary margin.
It is worth noting that you need to dig a hole even larger. Since you will have to backfill. If you chose the construction of a columnar concrete foundation from separate blocks, you will need to significantly expand the ditch for additional work to connect the parts. Monolithic products are much easier to install. To do this, it will be enough for you to drill a hole, it was possible to fill up a pillow and insert a post.
Foundation construction rules
As mentioned above, the supports must be placed at the corners of the building. Also, all load-bearing parts and other heavy elements must be supported on them. Typically, the frequency of the location of the bases ranges from 150 to 250 cm.This whole structure is united by a grillage, which evenly distributes the load between all components.
It is also required to make a zabirka, which will keep the heat inside, and also exclude the access of animals and moisture there. It is a brick or concrete partition. In conditions of heaving soils, this element is also installed on a pillow, and sometimes deepened into the ground by 20 cm.
Let’s consider step by step how the construction of a columnar foundation is independently carried out. The first step is to study the properties of the soil and draw up a detailed project..
Stakes are placed at specific points, so it is important to carefully mark the area. This is usually done with a taut rope, marking the necessary points for installation..
For this example, consider concrete foundation pillars. The indentations are made in a square or rectangular shape, while it is important to prevent deviations from the marking. If you are digging to a depth of more than one meter, it is necessary to ensure that the walls are tilted to prevent shedding. If the corner cannot be completed, then the sides are reinforced with formwork. You need to dig about 25 cm more than the level of the support. So that you can easily install the necessary spacers, it is recommended to take a margin of width.
Sand and gravel bedding
Such a pillow is needed for almost any type of foundation. For these purposes, take coarse sand and gravel. It is poured to a depth of about 25 cm and 15 cm wider than the size of the foundation pillar. Then the resulting mixture is abundantly moistened with water and carefully tamped. Then it is covered with a layer of any waterproofing material so that it does not absorb moisture from the concrete solution..
The best option would be to use a finished concrete product, which is installed on the pillow prepared at the previous stage. However, if you are using a monolith structure, then its foundations must be made the same. The width of this element should exceed the column by about 30%. When arranging it, it is advisable to make general fittings, which will significantly strengthen.
The pillar foundation is poured with a concrete mixture into the formwork. Instead of a frame, asbestos or metal pipes with the required section can be used. Concrete is poured into them, which, when solidified, forms a solid system. The fittings are usually selected with a diameter of at least 1 cm and placed at a distance of 20 cm from each other. The rods should protrude about 10 cm to ensure weld to the grillage.
If you decide to build supports from red brick, you must select fired products of grade 100 or higher, and cement for laying at least M300. To get elements of the same height, alignment must be carried out before setting, since then it will be much more difficult to do this..
How to build a grillage
After the device of the columnar foundation made of concrete pillars is ready and the mortar is completely dry, it is required to combine all the components with a single belt. Its lower part should be at a distance of more than 10 cm from the ground in order to protect against heaving of the soil. With a monolithic structure, the connection is made by pouring onto the common reinforcement. Prefabricated bases are fixed by welding. At the junction, a formwork is made, into which a mixture of a suitable brand is poured. It is necessary to dry the product in compliance with all requirements, regularly moistening with water.
Moisture has a negative effect on almost any material. The liquid coming from the surface can be limited by the blind area. In the case of a close location of groundwater, it is necessary to isolate the grillage. The pillars themselves are advised to be made of moisture-resistant concrete. There are several options for such protection:
bitumen is applied to the upper parts, which is then covered with roofing material. For greater reliability, such layers are repeated several times;
it is possible to lay a mix of cement and sand on top in a ratio of 1: 2. After drying, it is covered with a small sand pillow, which is covered with durable waterproofing materials..
As a rule, concrete structures are not subject to decomposition in an aggressive environment, so they may not be protected from moisture.
We reviewed the installation instructions for a columnar foundation, a photo of which you can see on our website conceptualhouseplans.com. Currently, most of the private houses use just such a framework. It gained such popularity due to its excellent operational characteristics, the possibility of making it with your own hands and a wide selection of raw materials for construction..
It is also the cheapest variety. However, during construction, it is necessary to comply with the established requirements and conduct surveys..