Substitution of soils. Replacement of weak soil

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 . Studies are conducted in a special laboratory. In the event that there is a risk of collapse of a building during its construction at a particular location, measures aimed at strengthening or replacing the soils may be carried out.

Classification

All soils are divided into several basic types:

• Rocky. They represent a solid rock massif. Do not absorb moisture, do not sink and are considered non-purulent. The foundation on these grounds is practically not buried. To the rocky also include coarse clastic soils, consisting of large fragments of rocks. In the event that the stones are mixed with clay soil, the soil is considered to be slightly stubbly, if it is sandy - non-stinging.
• Bulk. Soils with a disturbed natural structure of layers. Simply put, poured artificially. Buildings on a similar basis can be built, but you must first perform a procedure such as soil compaction.
• Clayey. They consist of very small particles (not more than 0.01 mm), absorb water very well and are considered to be puffy. Sled homes on such soils is much stronger than on rocky and sandy. All clay soils are classified into loam, sandy loam and clay. These include, among other things, loess.
• Sandy. They consist of large particles of sand (up to 5 mm). Such soils are very weakly compressed, but quickly. Therefore, the houses built on them, settle down to a shallow depth. Sand soils are classified according to the size of the particles. The best grounds are gravel sand (particles from 0.25 to 5 mm).
• Quicksands. Dusty soils, saturated with water. Most often occur in wetlands. For the construction of buildings are considered unfit.

Such classification by types is performed in accordance with GOST. Soils are examined in laboratory conditions with the definition of physical and mechanical characteristics. These surveys are the basis for calculating the capacity of foundations for buildings. According to GOST 25100-95, all soils are divided into rock and non-subsidence, subsidence and non-saline, saline and non-saline.

Basic Physical Characteristics

When carrying out laboratory tests, such parameters of soils are determined:

• Humidity.
• Porosity.
• Plastic.
• Density.
• Density of particles.
• Modulus of deformation.
• Resistance to shear.
• Angle of friction of particles.

Knowing the density of particles, you can determine and such an indicator as the specific gravity of the soil. First of all, it is calculated to determine the mineralogical composition of the earth. The fact is that the more organic particles in the ground, the lower its bearing capacity.

Which soils can be classified as weak

The procedure for conducting laboratory tests is also determined by GOST. Soils are examined using special equipment. The work in this case is carried out only by trained specialists.

If, as a result of the 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 structural integrity violation, the ground is recognized as weak. To such, for the most part, they include quicksand and loose soil. Weak, sandy, peaty and clayey soils with a high percentage of organic remains are also the weakest.

If the soil on the site is weak, the construction is usually transferred to another location with a more favorable base. But sometimes this is not possible. For example, in a small private area. In this case, it may be decided to erect a pile foundation with a depth of laying up to dense layers. But sometimes it seems more expedient to replace or strengthen the soil. Both these operations are quite costly in terms of both financial and time costs.

Substitution of soils: principle

The process can be performed in two ways. The choice of method depends on the depth of occurrence of dense layers. If it is not large, a weak soil with insufficient bearing capacity is simply removed. Further on a dense base of the underlying layer is poured a poorly compressed pillow from a mixture of sand, gravel, gravel and other similar materials. This method can be used only if the thickness of the layer of weak soil on the site does not exceed two meters.

Sometimes it happens that the dense soil is very deep. In this case, the pillow can be laid and on a weak one. However, in this case, it is necessary to perform accurate calculations of its dimensions in the horizontal and vertical planes. The wider it is, the less pressure due to the distribution of pressure will be on the weak ground. Such pillows can be used for foundation 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 will simply begin to bulge into the thick ground from all sides. The house itself will settle, and unevenly, which can lead to the destruction of its structural elements. In order to avoid this, sheet piling is installed along the perimeter of the cushion . Among other things, they prevent waterlogging of sand and gravel mixture.

Is it possible to change the soil on the site itself

Substitution of soils under the foundation must be carried out only with preliminary carrying out of the relevant studies and calculations. Of course, it will not work. Therefore, most likely, we will have to invite specialists. However, when building not too expensive buildings, for example, economic, this operation can be made and "by eye". Although we still would not advise taking risks, but for the general development, let's look at this procedure in more detail. So, the stages of work in this case are as follows:

• The excavation is carried out to a dense base.
• In the trench to the level of the base of the future foundation, sand of medium size is filled. Backfill is produced by layers of small thickness with a rammer of each. Before compacting, sand should be moistened with water. The jigging should be done as carefully as possible. In the sand itself, there should be no inclusions, especially large ones. Sometimes, instead of it, concrete mixtures and slags are used.

In the event that an artificial foundation is used for the foundation, it is also necessary to arrange a drainage system around the house. This will slightly increase the density of the surrounding soil pillow and prevent its extrusion into the sides.

Works on the creation of a drainage system

Next, consider how you can arrange a drainage system on the site. The walls of the foundation for reliability are best waterproofed. So, the features of the process:

• A meter away from the building is a ditch. The excavation is carried out below the foundation depth. Width - not less than 30 cm. The slope of the bottom of the trench must 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.
• On the sand spread Geotextile with the fixing of the edges on the stacks of the moat.
• Pour a ten-centimeter layer of gravel.
• Lay the perforated drainage pipe.
• Cover it with a gravel layer of 10 cm.
• Cover the "cake" with the ends of the geotextile and sew them.
• They fall asleep all over with soil, leaving observation cores in the corners of the building.
• At the end of the pipe, a well-receiver is arranged. Remove the drain at least five meters from the wall of the building.
• Gravel is poured on the bottom of the well and a plastic container with holes drilled in the bottom is placed there.
• Take the pipe into the container.
• On top, the well is covered with boards and sprinkled with earth.

Of course, the building itself should be mounted drainage system.

How is the soil strengthened?

Since the substitution of soils - the operation is quite laborious and expensive, it is often replaced by the procedure of strengthening the foundation for the foundation. In this case, several different methods can be used. One of the most common is the ramming of the soil, which can be shallow or deep. In the first case we use a tamping machine in the form of a cone. It is raised above the ground and dropped down from a certain height. This method is usually used to prepare for the construction of bulk soils.

Deep soil compaction is carried out using special piles. They are slaughtered in the ground and pulled out. The resulting pits are covered with dry sand or poured with concrete.

Thermal method

The choice of the option of strengthening the soil depends, first of all, on its composition, the procedure for determining which is regulated by GOST. Soils, the classification of which was presented above, usually require reinforcement only if they belong to a non-scallop group.

One of the most common methods of amplification is thermal. It is used for loess soils and allows to perform a reinforcement to a depth of about 15 m. In this case, very hot air (600-800 degrees Celsius) is injected into the ground through the pipes. Sometimes the thermal treatment of the soil is done in a different way. Wells are digging into the ground. Then they combust combustible products under pressure. Pre-boreholes are hermetically sealed. After such treatment, the calcined soil acquires the properties of a ceramic body and loses the ability to collect water and swell.

Cementation

The sandy soil (photo of this species is presented below) is strengthened in a somewhat different way - cementation. In this case, pipes are jammed into it, through which cement-clay mortars or cement slurries are pumped. Sometimes this method is used to seal cracks and cavities in rocky grounds.

Silicification of soils

On quicksand, dusty sandy and macroporous soils, the method of silicification is more often used. To enhance this, a solution of liquid glass and potassium chloride is injected into the pipes . The injection can be done to a depth of more than 20 m. The radius of distribution of liquid glass often reaches one square meter. This is the most effective, but also the most expensive method of amplification. A small specific gravity of the soil, as already mentioned, indicates the content of organic particles in it. In some cases this composition can also be enhanced by silicification.

Comparison of the cost of replacement and strengthening of the soil

Of course, the reinforcement operation will be cheaper than full replacement of the soil. For comparison, let's first calculate how much it will cost to create an artificial gravel ground for 1 m ³ . Select the land from one cubic meter of the area will cost about 7 cu. The cost of rubble is 10 cu. For 1 m ³ . Thus, the replacement of a weak ground will cost 7 cu For a dump plus 7 cu For moving gravel, plus 10 cu For the gravel itself. Total 24 USD. Strengthening of soil costs in 10-12 cu, which is twice cheaper.

From all this we can draw a simple conclusion. 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, it is necessary to consider the option of erecting a building on stilts. Strengthening and replacing the soil 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 the regulations, are strengthened by methods appropriate to their specific composition.