Before starting the construction of the foundation of the house, an operation such as checking the bearing capacity of the soil must be carried out without fail. Research is conducted in a special laboratory. In the event that there is a risk of collapse of the building during its construction at this particular place, measures can be taken aimed at strengthening or replacing soils.
Classification
All soils are divided into several main types:
- Rocky. They are a solid rock mass. They do not absorb moisture, do not sag and are considered non-porous. The foundation on such grounds is practically not deepened. Coarse soils consisting of large rock fragments are also referred to rocky . In the event that the stones are mixed with clay soil, the soil is considered to be slightly downy, if with sand - non-downy.
- Bulk. Soils with a disturbed natural layering structure. Simply put, poured artificially. Buildings on a similar basis can be built, but you must first perform a procedure such as compaction of the soil.
- Clayey. They consist of very small particles (not more than 0.01 mm), absorb water very well and are considered heaving. Sinking houses on such soils are much stronger than on rocky and sandy. All clay soils are classified into loam, sandy loam and clay. These include including loess.
- Sandy. Consist of large particles of sand (up to 5 mm). Such soils are compressed very weakly, but quickly. Therefore, houses built on them are settled to a shallow depth. Sandy soils are classified by particle size. The best bases are gravelly sands (particles from 0.25 to 5 mm).
- Quicksandies. Dusty soils saturated with water. Most often found in wetlands. For the construction of buildings are considered unsuitable.
Such classification by type is performed according to GOST. Soils are examined in laboratory conditions with the determination of physical and mechanical characteristics. These surveys are the basis for calculating the power of foundations for buildings. According to GOST 25100-95, all soils are divided into rocky and non-rocky, subsidence and non-subsidence, saline and non-saline.
Basic physical characteristics
During laboratory research, the following soil parameters are determined:
- Humidity.
- Porosity.
- Plastic.
- Density.
- Particle density.
- Deformation modulus.
- Shear resistance.
- Particle friction angle.
Knowing the particle density, one can also determine such an indicator as the specific gravity of the soil. It is calculated primarily for determining the mineralogical composition of the earth. The fact is that the more organic particles in the soil, the lower its bearing capacity.
What soils can be classified as weak
The procedure for laboratory testing is also determined by GOST. Soils are examined using special equipment. In this case, only trained specialists carry out the work.
If as a result of tests it is revealed that the mechanical and physical characteristics of the soil do not allow building structures and buildings on it without the risk of their collapse or violation of the integrity of the structure, the soil is considered weak. These for the most part include quicksand and bulk soil. Loose sandy, peaty and clayey soils with a large percentage of the content of organic residues are also recognized as weak ones most often.
If the soil on the site is weak, the construction is usually transferred to another place with a better foundation. But sometimes this is not possible. For example, in a small private plot. In this case, a decision may be made on the construction of a pile foundation with a depth of laying to dense layers. But sometimes the procedure for replacing or strengthening the soil seems more appropriate. Both of these operations are quite expensive in terms of both financial and time costs.
Substitution of soils: principle
The process can be carried out in two ways. The choice of method depends on the depth of the dense layers. If it is small, weak soil with insufficient bearing capacity is simply removed. Then a poorly compressible pillow of a mixture of sand, gravel, gravel and other similar materials is poured onto the dense base of the underlying layer. This method can only be used if the thickness of the layer of soft soil in the area does not exceed two meters.
Sometimes it happens that dense soil is located very deep. In this case, the pillow can also be laid on a weak one. However, in this case, accurate calculations of its dimensions in the horizontal and vertical planes should be performed. The wider it is, the smaller the load on soft soil will be due to pressure distribution. Such pillows can be used in the construction of foundations of all types.
When using such an artificial base, there is a risk of crushing the pillow by the weight of the building. In this case, it simply begins to protrude into the thickness of weak soil from all sides. The house itself will sag, and unevenly, which can lead to the destruction of its structural elements. To avoid this, sheet piles are installed around the perimeter of the pillow. Among other things, they prevent waterlogging of the sand-gravel mixture.
Is it possible to change the soil on the site yourself
Substitution of soils under the foundation should be carried out only with the preliminary conduct of appropriate research and calculations. To do such a job yourself, of course, will not work. Therefore, most likely, you will have to invite specialists. However, when erecting not too expensive buildings, for example, household ones, this operation can also be performed “by eye”. Although we would not advise taking risks, but for general development, let's understand this procedure in more detail. So, the stages of work in this case are as follows:
- Excavation is carried out to a dense base.
- Medium-sized sand is poured into the trench to the level of the bottom of the future foundation. Backfill is made in layers of small thickness with each tamper. Sand must be dampened with water before compaction. Ramming should be carried out as carefully as possible. In the sand itself there should not be any inclusions, especially large ones. Sometimes instead of it concrete mixes and slags are used.
In the event that an artificial foundation is used for the foundation, it is also worthwhile to arrange a drainage system around the house. This will slightly increase the density of the soil surrounding the pillow and prevent its extrusion to the sides.
Work on the creation of a drainage system
Next, we will consider how to arrange a drainage system in the area. Foundation walls for reliability are best waterproofed. So, the features of the process:
- A meter from the building dig a moat. The excavation is performed below the depth of the foundation. Width - not less than 30 cm. The slope of the bottom of the trench should be at least 1 cm per 1 m of length.
- The bottom of the trench is rammed and covered with a five-centimeter layer of sand.
- Geotextiles are spread on the sand with edges fixed on the ditch stacks.
- Pour a ten-centimeter layer of gravel.
- Stack the perforated drainage pipe.
- They fill it with gravel with a layer of 10 cm.
- Cover the “pie” with the ends of the geotextile and stitch them together.
- They fill everything with soil, leaving observation wells in the corners of the building.
- At the end of the pipe, a well-receiver is arranged. It is necessary to divert the drain at least five meters from the wall of the building.
- At the bottom of the well, gravel is poured and a plastic container with holes drilled in the bottom is installed there.
- Take the pipe into the tank.
- From above the well is covered with boards and sprinkled with earth.
Of course, the gutter system should be mounted on the building itself.
How is soil reinforcement
Since soil displacement is a rather laborious and costly operation, it is often replaced by a foundation reinforcement procedure. In this case, several different methods can be applied. One of the most common is the compaction of soil, which can be superficial or deep. In the first case, ramming in the form of a cone is used. It is raised above the ground and thrown down from a certain height. This method is usually used for preparation for the construction of bulk soils.
Deep compaction of the soil is carried out using special piles. They are driven into the ground and pulled out. The resulting pits are covered with dry sand or flooded with soil concrete.
Thermal method
The choice of soil reinforcement option depends primarily on its composition, the determination procedure of which is governed by GOST. Soils, the classification of which was presented above, usually require reinforcement only if they belong to a non-rock group.
One of the most common amplification methods is thermal. It is used for loess soils and allows for strengthening to a depth of about 15 m. In this case, very hot air (600-800 degrees Celsius) is pumped into the ground through pipes. Sometimes thermal soil treatment is done differently. Wells are dug into the ground. Then, combustible products are burned in them under pressure. Previously, the wells are hermetically sealed. After this treatment, the calcined soil acquires the properties of a ceramic body and loses its ability to collect water and swell.
Cementation
Sandy soil (photo of this variety is presented below) is strengthened in a slightly different way - cementation. In this case, pipes are clogged into it, through which cement-clay mortars or cement slurries are pumped. Sometimes this method is used to seal cracks and cavities in rocky soils.
Silicate soil
On quicksand, dusty sandy and macroporous soils, the method of silicatization is often used. To enhance this, a solution of liquid glass and potassium chloride is injected into the pipes . Injection can be done to a depth of more than 20 m. The spread radius of liquid glass often reaches one square meter. This is the most effective, but also the most expensive way to amplify. The small specific gravity of the soil, as already mentioned, indicates the content of organic particles in it. Such a composition in some cases can also be enhanced by silicatization.
Comparison of the cost of replacement and soil reinforcement
Of course, the amplification operation will cost less than a complete soil replacement. For comparison, let's first calculate how much it will cost to create artificial gravel soil per 1 m 3 . Choosing land from one cubic meter of area will cost about 7 cu The cost of crushed stone is 10 cu for 1 m 3 . Thus, the replacement of soft soil will cost 7 cu for the recess plus 7 cu for moving gravel, plus 10 cu for gravel itself. Total 24 cu Soil strengthening costs 10-12 cu, which is two times cheaper.
From all this a simple conclusion can be drawn. In the event that the soil on the site is weak, you should choose another place for the construction of the house. In the absence of such an opportunity, you need to consider the option of building a building on stilts. Reinforcement and soil replacement are carried out only as a last resort. When determining the need for such a procedure, SNiP and GOST should be guided. Soils, the classification of which is also determined by standards, are enhanced by methods suitable for their specific composition.