- Compaction method
- Vibrating method
- Pillow device
- Strengthening soft ground
- Concrete preparation
There are many different factors to consider when preparing soil prior to construction. Particular attention should be paid to the type and composition of the soil. It can be stable (this is the best option) or weakened and unstable. In the first case, the usual concrete preparation is used, which consists in pouring a concrete pad. This is the simplest option, in which you do not need to use complex construction equipment and expensive materials. Such preparation consists in the fact that first the sand bed is laid, after which the concrete mixture of cement is already poured.
Layout of the "pie" of the foundation.
If the soil is weak and unstable, the soil must be strengthened. For this, tamping, strengthening with the help of special mixtures that are introduced by injection methods are preliminarily carried out.
Compaction method
For clayey weak soils, loose sand, loess soil, the compaction method is carried out. To do this, a rammer with a mass of 5 to 15 tons is dropped onto the prepared soil, the dumping height is 4-8 m.The diameter of such a rammer is 1-3 m.
Heavy rammers are used when it is necessary to work with very difficult soils, loose sand, clayey weak soils. The rammer can be made of steel or reinforced concrete, it has the shape of a truncated cone, the center of gravity is quite low here. All this ensures the verticality of the rammer fall, impact density.
The maximum efficiency of using this method is achieved with optimal moisture. If the soil is not moist enough, then it is best to pre-moisten it so that the working conditions are the best.
The compaction method must take into account the number of discharges. Otherwise, this method will do more harm than good. For different types soil failure value is its own:
- sandy soils - 0.05-1 cm;
- silty clay soils - 1-2 cm.
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Vibrating method
Soil compaction by injection method: 1 - concrete screed, 2 - parker, 3 - coupling, 4 - injector, 5 - injector nozzle, 6 - place of planned hydraulic fracturing, 7 - vector of force impact on the soil.
Deep soil compaction can be used to prepare the foundation by vibration. The process of such preparation includes the following operations:
- pit preparation;
- the soil is moistened, for which a tubular perforated needle is placed in the soil. The immersion depth is 2-2.5 m. Water is supplied through this needle.
To moisten 1 cubic meter of sand, it is necessary to supply approximately 50-70 liters of water. The vibrator head is immersed next to the needle, vibration is produced for about 20-30 seconds. After the compaction is over, the needle is removed from the soil, followed by the vibrator head. One immersion and compaction process takes up to three minutes. All dive points must be staggered.
The use of a hydraulic vibrator makes it possible to compact the soil to a depth of 6-7 m.
For compaction with silted and clayey soils, special soil and sand piles are used. The diameter of such pipes is 400-500 mm; a shoe is mounted at the end. The immersion of such pipes is carried out by a crane or a head.
When immersed, the tip of the pipes compacts the soil, while its shell is filled with sand, which is compacted in layers. The pipe is retracted as it fills. This method is used to work with loess subsidence soils.
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Pillow device
To ensure the correct load on the future foundation, it is necessary to use sand and gravel fill before using almost any method (especially for concrete cushions). Only sifted sand or crushed stone (gravel) is used, which is poured over a previously prepared base.
Sand is poured onto the bottom of the pit. Its thickness, as a rule, is from 3.5 to 20 cm. Sand (or gravel) is poured to the bottom, after which it is leveled and moistened with water. The layer should not be wet, only slightly damp - this is an important condition that should not be neglected. It is necessary to compact the bedding with a special vibrator. After that, the surface is covered with a cement screed.
If the level groundwater in the selected area is quite high, then sand or gravel is poured directly into the water. It is compacted with a special deep vibrator. A layer of crushed stone is poured on top, after which the compaction is performed using a surface vibrator or a conventional mechanical rammer.
When choosing a material, it is necessary to take only cleaned sand, gravel or crushed stone, it is recommended to use a medium fraction, homogeneous.
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Strengthening soft ground
Scheme of soil strengthening by the "Geocomposite" method.
When building on weak and unstable soils, it is necessary to carry out strengthening work, which includes cementation, that is, injection of concrete solution. There can be several methods of such strengthening:
- silicatization consists in the fact that after clearing the site for work, special injectors are immersed in the soil, pumping them through prepared solutions. After that, the injectors are removed, the wells are plugged. For loess soils, only solutions with sodium silicate are used, which, interacting with calcium salts, turn into a dense gel. It solidifies into a very hard mass;
- resinization by the principle of use is similar to silicatization;
- thermal strengthening is the consolidation by burning the material. In this capacity are gas, some types of liquid fuel. The material is pumped into a pre-prepared well; combustion is performed by pumping air with excess pressure;
- cementation is one of the varieties concrete preparation, which is used to strengthen rock fractured rocks, sandy loose, gravelly soils. At the same time, wells are being cleaned and drilled. After that, special injectors are introduced into the prepared wells, through which cement mortar is pumped into the soil. After work, the injectors are removed, the wells are plugged.
The difference in the quality of the foundations of houses depends not only on the materials used for the construction, but also on how the place was prepared before construction began. When building a house, it is worth deciding whether concrete preparation is suitable for the foundation, as the highest quality and most stable, or it is better to choose another for this soil. Sandy or crushed stone preparation is less reliable, more difficult to create, but cheaper in building materials and installation time.
Most often, concrete preparation is used for a flooded foundation or to increase the strength and stability of the base of the house.
Reasons to build a foundation:
- Additional waterproofing, which slows down the rise of moisture from the soil into the foundation.
- Smooth construction site, removes any irregularities left when the excavation pit by technicians or builders, allows you to level the differences up to 10 cm.
- Prevents the absorption of "concrete milk" into the soil, due to the fact that concrete pouring is not carried out on open ground, but on a solid base, the base when solidified has the same density, which increases its performance.
- Facilitates the installation of reinforcement, makes it possible to use clamps, protecting the base reinforcement from corrosion.
- Eliminates the bending of the reinforcement due to pressing into the ground under the weight of uncured concrete.
What are the types of preparations
Preparing the site for a monolithic or strip foundation, can choose different materials depending on the desired characteristics, budget and difficulty in installing on your own. The main reasons for choosing this or that option are the endurance of the soil, its moisture content, whether a basement or basement is planned. It is also important what type of support will be used, not buried, shallow or buried. From what materials, and in what way it will be erected, by pouring or from ready-made blocks, tape or slab.
Unfortunately, SNiP 52-01-2003 and SP 50-101-2004 do not give clear recommendations in which case and what kind of preparation to conduct, so the reason for choosing is the type of foundation and the materials used for it.
Sand preparation
The easiest and cheapest way to level the ground for construction is sand preparation under the base, for light wooden houses used quite often, but not suitable for houses with an estimated service life of more than 10 years. It is unreliable, gradual mixing with the soil and germination by plant roots causes subsidence under the weight of the building, distortions and cracks of floors and walls are possible. Low moisture resistance requires additional waterproofing to prevent dampness in the premises.
Concrete preparation
Used "lean" concrete with a maximum of 6% cement, the main filler is sand, sometimes crushed stone or gravel. It is poured in a thin layer over the entire area of \u200b\u200bthe future foundation, the thickness of the concrete preparation depends on the type of soil, the weight of the house and the level of groundwater. Depending on these three factors, the thickness can be from 4 to 10 cm.
Membrane preparation from profile
A new method of foundation preparation, easy to install and less expensive than concrete or crushed stone. Despite the assurance of the manufacturers of strength and similar durability, it is in less demand.
If possible, they often choose proven footings. Due to the additional costs of thermal insulation, the cost can be as high as the cost of standard preparation.
Crushed stone preparation
Crushed stone preparation for the foundation is used if there is no reinforcement or uneven weight distribution. Crushed stone is covered with a thickness of 15 to 20 cm, filling it with bitumen until a film is formed or the layer is completely impregnated. For heavy houses, it is unreliable due to the heterogeneity of crushed stone, can lead to warping and cracks in the foundation and walls.
In the cold season, crushed stone preparation is almost never used due to the difficulty of creating the required temperature for bitumen pouring.
Preliminary work before pouring the concrete
The construction of the foundation and preparation for it begins with geotechnical work in order to find out how deep the groundwater lies, and how much pressure the earth can bear at the site of the future house. A construction plan is drawn up and the type of foundation is selected, monolithic or strip, cast or prefabricated.
Before creating a concrete pad, it is necessary to mark the territory in order to dig a pit. It should make it possible to make a formwork for pouring, therefore, on each side of the future support, an indent of at least 30 cm is made.
The fertile soil layer is removed and transferred to another place where it can be used. In depth, the pit for the foundation must be at least 20 cm more than the planned height of the support.
If thermal insulation is laid, then the depth of the pit is increased by the width of the additional layers.
Lean concrete preparation method
Concrete is called skinny because of its very low cement content, which, due to its fragility, makes it useless in full-fledged construction, but ideal for concrete preparations for the foundation. Depending on the resistance, the choice is provided by 2 classes of concrete mixtures, these are B7.5 and B15, the latter is more difficult to use due to the high content of expanded clay.
To obtain a cubic meter of the finished solution from B7.5, you need:
- 160 kg of cement, this is 6.4 bags of cement weighing 25 kg;
- 2.2 tons of sand;
- 75 liters of water.
All components must be mixed well and poured onto the prepared area.
When making B15, a special technique is needed to obtain a homogeneous consistency of the finished mixture.
Monolithic slab foundation
10 cm of crushed stone or sand is poured onto the cleaned space and tamped with a vibrating plate. This is done to wick excess moisture away from the substrate, making it last longer.
A formwork is mounted on the crushed stone pad, into which the concrete mass from B7.5 cement will be poured. The formwork is made of such a height that the poured concrete forms an even top, on which the base of the house will be laid. It should be at least 10 cm high and maximum 30 cm high.
Often, when installing the formwork, it is advised to make a concrete preparation device for the foundation with a margin of 10-30 cm relative to the foundation. This is done in order to reduce the pressure on the ground and leave room for thermal insulation and finishing work, which prevent the destruction of the foundation from the side of the walls.
Concrete is poured flush with the top of the formwork, leveled and sometimes tamped using a vibrating plate. For better adhesion to the cast foundation slab, rods of 0.8 cm in diameter are installed in the footing, protruding by 10 cm from the preparation, if the base is planned to be large, then the footing will have to be poured in parts in order to insert the connecting reinforcement.
If a ready-made concrete slab is bought, and not poured, then the rods are not installed.
The thin concrete layer is then left to dry for 7-21 days, depending on the weather. Sometimes for heavy buildings, the substrate is reinforced with a mesh with reinforcement of 0.8 cm in cross section. In addition, the size of such a substrate must be at least 15 cm.
If the connecting rods have not been installed in the substrate, then it is advised to put waterproofing, EPPS thermal insulation, and then waterproofing again on the finished flooring. After that, you can mount the casting formwork monolithic slab the basics.
How concrete preparation is poured and insulated can be seen in the video:
Concrete for strip base
Concrete preparation for a strip foundation is different from preparation for a slab. Dig a trench that is 40 cm wider on each side of the foundation tape. Level the bottom of the trench and lay waterproofing. Formwork is mounted with a height of 20-30 cm and concrete mixture is poured.
The width of the footing tape should be 15 cm greater than the base on each side. If you plan to use a cast strip foundation, the concrete is reinforced with rods for better adhesion.
When the buried strip base is built from ready-made blocks, it is advisable to use preparation from crushed stone, impregnated with bitumen, compacted with a vibrating plate. Sometimes waterproofing is placed on top and a second layer of concrete is poured for better resistance to destruction.
For shallow or shallow foundations on stable soils, it is possible to level off with sand or compacted rubble without bitumen. Such a foundation, due to the lightness of the building, does not require serious strengthening.
Preparation for a columnar foundation
For a pile foundation, they are more often used sand preparation because of the functions of the foundation itself. It is installed for light houses and on stable soils. Most often, it does not require additional amplification. If the house under construction is heavy enough, then crushed stone filled with bitumen is used. The concrete substrate is used extremely rarely, because of the opportunity to buy small concrete slabs, which are more reliable than poured ones.
Whatever the foundation and the house, in most cases, concrete preparation will extend the service life and, by spending money during the construction phase, prevent spending on more expensive base repairs.
Why is SNiP necessary for concrete preparation under the foundation, and what requirements does it set for builders? What are these rules and regulations? These questions arise in the minds of many masters, both beginners and experienced.
In this article, we will help you understand these issues and explain everything in an accessible way.
Photo of preliminary concrete foundation
Preparatory work for the construction of foundations
Preparation of the foundation for the house should include the following steps:
- preliminary calculations;
- preparation of the base site;
- preparation for the foundation.
Here we will dwell on the last of the listed stages. In principle, a pillow under the base is made either from compacted rubble, or from lean concrete and it is easy to do it yourself.
Technical requirements govern the layer thickness building material, which the concrete preparation for the foundation should have as well as the technology of work. The basic norms and requirements for the preparation of the base are contained in SNiP 52-01, SP 50-101-2004 and SP 52-101-2003.
The main task of this stage of work is preparation for the actual construction of the foundation. Existing building regulations provide different kinds these works, but the main one is the foundation.
Assigning a foundation for monolithic structures
- Protects the concrete mass from the flow of cement mortar. This contributes to a more rapid achievement of the required parameters of the base with an overall improvement in its quality;
- Negates the effect of forces from the soil. The foundation distributes the forces that arise in the soil;
Soil force distribution diagram
- Provides additional convenience for reinforcing a monolithic structure. The smooth surface facilitates work on the precise alignment of the base skeleton.
Types of preliminary work
The above building rules indicate two types of base preparation:
The use of crushed stone preparations is solely due to a decrease in the cost of construction (the price of crushed stone is generally available) and cement savings. In this case, the layer of rubble should be 20 cm, which should be well tamped. After compaction, it is filled with bitumen.
Crushed stone pad before pouring with bitumen
Note!
This is an unreliable method that has a serious drawback - insufficient substrate rigidity.
The result of this is the impossibility of ensuring the maximum convenience of the subsequent foundation work.
Naturally, for the construction of critical structures of this type should be avoided. However, for auxiliary, technical or auxiliary buildings, its use is quite acceptable to reduce the cost of construction work.
Concrete preparation
The device of concrete preparation for the foundation is becoming relevant for the construction of reinforced tape or slab structures... The main reason is that with such technologies for erecting foundations, a rigid installation of steel meshes and frames is assumed before pouring the concrete mixture.
An additional reason is associated with the fact that on a rigid surface, the construction of the foundation is simplified in principle.
Important. This method is of particular importance when construction works in winter, when the soil deteriorates.
The main theses that the instruction and rules contain:
- The rules allow the use of concrete M50 and higher for concreting.
- A total layer thickness of 10 cm is usually enough not only to level the site, but also to form solid foundation under the foundation being built.
- A layer of concrete is laid out on a cushion of sand or gravel.
Sand and crushed stone cushion
Sand preparation for the foundation provides an optimal redistribution of the load on the lower part of the foundation, which is relevant due to the fact that the soil undergoes seasonal changes in spring and autumn.
With the help of a sand cushion, the lower part of the foundation can be raised above the groundwater level and smooth out the deforming effects of foreign objects and materials due to the obstacle to direct contact.
Council. It makes sense to arrange a sand pillow if there is problem soil at the bottom of the pit.
In this case, the soil layer is removed and in its place coarse river sand is poured with a layer of at least 150 mm.
After that, it is leveled using simple levels and rammed with a special tool - a rammer.
Sand cushion ramming
High quality sand pillow can be laid when taking into account the level of groundwater and their seasonal changes. When high level it may be necessary to build a drainage layer (which, however, will not be superfluous in any case).
Layout of the sand cushion
To do this, a trench is dug around the perimeter of the structure under construction, which protects against melt water and an increase in the level of groundwater during heavy precipitation. This trench must be properly waterproofed. Drainage will prevent basement flooding.
Instead of sandy, crushed stone preparation for the foundation can be used. It is stronger than its competitor. The material is crushed stone of 20/40 mm fraction. A small layer of coarse sand (10-15 cm) is poured under a layer of crushed stone of 20-25 cm.
Crushed stone must be tamped with a vibrating plate. After compaction, the top layer of material should be at the zero mark.
Cushion scheme using rubble
Important. The presence of a cushion determines the distance from the surface of the foundation to the reinforcement, which is called a cover.
When using a concrete pad, this layer can be halved from the standard 7 cm - up to 3.5 cm.
Sequence of work on concreting
- After laying the cushion, the formwork for the foundation is erected. height in thickness concrete basebut not higher than 30 cm;
- Metal rods (8-12 mm) are stacked. Reinforcement will give the pillow additional strength and reliability;
- Concrete is poured;
- The final compaction of the concrete cushion is carried out with a deep vibrator.
Important. The concrete pad should protrude at least 15 cm over the entire base area.
After pouring the pillow, pieces of reinforcement are inserted into it so that they protrude 20-30 cm.
They must provide a bond of the pillow with the future base.
Tie reinforcement diagram
findings
The current standards in construction assume preliminary preparation for foundations that can be made either from crushed stone with bitumen, or from concrete.
A concrete pad is in every way optimal solution, because it not only ensures better reliability of the future foundation, but also simplifies the subsequent stages of work.
In the video presented in this article, you will find additional information on this topic.
Why is concrete preparation necessary for the future foundation?
Before building the foundation, in addition to preliminary calculations, you need to prepare the construction site. The so-called concrete preparation for the foundation is needed first of all. It consists in erecting a pillow under the base.
There are a number technical requirementsregulating the technology of preparatory work, the choice of material and the thickness of the layer used for the pillow. The list of basic norms and requirements for pre-foundation preparation is set out in SNiP 52-01, SP 52-101 / 2003 and SP 50-101 / 2004. They contain a lot of information on the topic that interests us. Basically, the role of fundamental preparation is as follows.
Basic functions of the foundation
If the base is planned to be poured in place, and not erected from ready-made blocks, preparation for the foundation will help:
- Protect the concrete mix from slurry leaks. This will accelerate the collection of the required volume by the foundation and the overall improvement of its quality indicators.
- To neutralize the force effects arising under soil pressure. Concrete preparation redistributes the forces that arise in the soil and weakens their negative impact on the foundation.
- Provide comfortable conditions for the preparation of the base reinforcement cage, which can be mounted on a flat surface.
Types of preliminary work
According to SNiP 52-01, for concrete preparation for the foundation, crushed stone, lean concrete (it has a low content of binders, respectively, a low grade - from M50) or profile membranes are used as the main material.
Crushed stone with bitumen
Crushed stone preparations are used to reduce the total cost of the foundation and reduce cement consumption. The thickness of the crushed stone layer should be from 20 cm. After thorough compaction, the crushed stone is poured with bitumen. Crushed stone preparation is used in cases where it is necessary to fill the foundation of the excavation with bitumen until the soil is saturated to the maximum or the formation of a bituminous film.
The use of crushed stone preparation of the foundation cannot provide sufficient rigidity of the substrate. In addition, it is not very convenient to erect a base on a crushed stone substrate. Therefore, it is used in the construction of auxiliary ancillary and technical buildings to minimize costs.
Concrete preparation
It is needed to ensure the correct process of erecting a concrete foundation and to exclude soil subsidence. Skinny concrete is not a cheap option, however, it is used quite often. In such concrete, no more than 6% cement, the rest is crushed stone and gravel. The thickness of the concrete preparation layer should be 50 - 100 mm. It depends on the weight of the future building, the level of groundwater and the type of soil.
Concrete preparation for the foundation is used, first of all, in the construction of slab and strip reinforced structures. This is due to the peculiarities of the technological process, which provides for the rigid installation of frames and steel grids in the body of the future foundation before pouring it with concrete. In addition, it is much easier to build a foundation on concrete, especially in winter.
Profile membranes
A modern way of preparing a foundation that can replace crushed stone and concrete preparation. When laying them, "wet" types of work are excluded, money is saved, and the construction process is accelerated.
How to equip concrete preparation
The work must be done in the following sequence:
- First, you need to mark the construction site for the foundation device.
- The site needs to be leveled and covered with rubble with a layer of 10 cm.
- Use a vibrating plate to compact the pillow.
- Mark the perimeter and mount the formwork with a height of no more than 30 cm. Its height will depend on the thickness of the concrete layer.
- It is necessary to pour concrete mixture under the upper edge of the formwork.
- With the help of reinforcement, the pillow is reinforced using rods with a cross section of at least 8 cm.
- The concrete must be compacted using a vibrating plate.
- After pouring the site with concrete, reinforcement rods must be installed in it, the task of which is to fasten the foundation to the pillow. They should protrude above the concrete by about 20-30 cm.
On each side of the perimeter, you must retreat outside foundation slab by 10-15 cm, thereby increasing the size of the concrete preparation area. For a foundation made by the method concrete pouring no application restrictions. It is considered so reliable that its reinforcement is not necessary. In practice, both options have proven themselves from the most positive side. Their only difference is that the non-reinforced concrete pad has limited dimensions.
Construction requirements stipulate a minimum height of the concrete layer, which must rise above the ground surface by at least 15 cm. This allows optimal placement of the mesh for reinforcement. The mesh is used to reinforce the bottom of the concrete pad, which is experiencing tensile forces. They are transmitted from the foundation, which is subject to the weight load of the entire structure.
To understand why concrete preparation for the foundation is needed, one must carefully study the current regulatory documents. They say that any option for concrete preparation is better than none. It will provide the building with the best possible strength and stability, helping the foundation long time maintain the entire structure in good condition.
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