Before starting the construction of the foundation of the house, such an operation as checking the bearing capacity of the soil must be carried out without fail. Research is carried out in a special laboratory. In the event that it is revealed that there is a risk of a building collapsing during its construction at a given specific location, measures can be taken to strengthen or replace soils.
Classification
All soils are divided into several basic 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. Rocky soils also include coarse-grained soils, consisting of large fragments of rocks. In the event that stones are mixed with clay soil, the soil is considered to be weakly heaving, if with sandy soil, it is not.
- Bulk. Soils with disturbed natural layering structure. In other words, artificially poured. Buildings can be built on such a foundation, but a procedure such as soil compaction must first be performed.
- Clay. They consist of very small particles (no more than 0.01 mm), absorb water very well and are considered heaving. Houses sink on such soils much more strongly,than on rocky and sandy ones. All clay soils are classified into loam, sandy loam and clay. These include loess.
- Sandy. They consist of large sand particles (up to 5 mm). Such soils are compressed very weakly, but quickly. Therefore, houses built on them settle down to a shallow depth. Sandy soils are classified according to particle size. Gravel sands (particles from 0.25 to 5 mm) are considered the best bases.
- Quicksnappers. Dusty soils saturated with water. Most often found in wetlands. Buildings are considered unsuitable for construction.
This classification by type is carried out 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 capacity 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.
Main physical characteristics
During laboratory studies, the following soil parameters are determined:
- Humidity.
- Porosity.
- Plasticity.
- Density.
- Particle density.
- Deformation modulus.
- Shear resistance.
- The friction angle of particles.
Knowing the density of particles, it is possible to determine such an indicator as the specific gravity of the soil. It is calculated, first of all, to determine the mineralogical composition of the earth. The fact is that the more organic particles in the soil, thelower 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 is carried out only by trained specialists.
If, as a result of testing, it is revealed that the mechanical and physical characteristics of the soil do not allow the construction of 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 high percentage of organic residues are also most often recognized as weak soils.
If the ground 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, on a small private plot. In this case, a decision can be made to build a pile foundation with a laying depth of up to dense layers. But sometimes it seems more appropriate to replace or strengthen the soil. Both of these operations are quite expensive in terms of both financial and time costs.
Soil Replacement: Principle
The process can be done in two ways. The choice of method depends on the depth of dense layers. If it is small, weak soil with insufficient bearing capacity is simply removed. Next, a poorly compressible pillow is poured onto the dense base of the underlying layer.from a mixture of sand, crushed stone, gravel and other similar materials. This method can only be used if the thickness of the soft soil layer on the site does not exceed two meters.
Sometimes it happens that the dense ground is 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 less will be the load on weak soil due to the distribution of pressure. Such pillows can be used when constructing foundations of all types.
When using such an artificial base, there is a risk of crushing the pillow with the weight of the building. In this case, it will simply begin to bulge into the thickness of the weak soil from all sides. The house itself will sag, and unevenly, which can lead to the destruction of its structural elements. In order to avoid this, sheet piling is installed around the perimeter of the pillow. Among other things, they prevent waterlogging of the sand and gravel mixture.
Is it possible to change the soil on the site yourself
Replacement of soils under the foundation should be carried out only with the preliminary conduct of appropriate studies and calculations. Doing this on your own, of course, will not work. Therefore, most likely, it will be necessary to invite specialists. However, when erecting not too expensive buildings, for example, household ones, this operation can be performed “by eye”. Although we still would not advise taking risks, but for the general developmentLet's take a closer look at this procedure. So, the stages of work in this case are as follows:
- Digging to a solid foundation.
- Sand of medium size is poured into the trench to the level of the sole of the future foundation. Backfilling is done in layers of small thickness with ramming of each. The sand must be moistened with water before compaction. Tampering should be carried out as carefully as possible. There should be no inclusions in the sand itself, especially large ones. Sometimes soil-concrete mixtures and slags are used instead.
In the event that an artificial foundation is used under 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 it from being squeezed out to the sides.
Drainage system works
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 ditch is being dug a meter away from the building. Excavation is carried out below the depth of the foundation. 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.
- Geotextiles are spread on the sand with the edges fixed on the moat stacks.
- Pour a ten-centimeter layer of gravel.
- Laying the perforated drain pipe.
- They fill it with gravel with a layer of 10 cm.
- Cover the "pie" with the ends of the geotextile and sew them together.
- They cover everything with soil, leaving manholes at the corners of the building.
- A receiving well is arranged at the end of the pipe. You need to take the drain at least five meters from the wall of the building.
- Gravel is poured into the bottom of the well and a plastic container with holes drilled in the bottom is placed there.
- They take the pipe into the container.
- The top of the well is covered with boards and sprinkled with earth.
Of course, a drainage system should be installed on the building itself.
How soil is reinforced
Since soil replacement is a rather time-consuming and expensive operation, it is often replaced by the procedure of strengthening the base for the foundation. This can be applied in several different ways. One of the most common is soil compaction, which can be surface or deep. In the first case, a rammer in the form of a cone is used. It is lifted above the ground and dropped down from a certain height. This method is usually used to prepare for the construction of bulk soils.
Deep compaction of the soil is carried out using special piles. They are hammered into the ground and pulled out. The resulting pits are covered with dry sand or filled with soil concrete.
Thermal method
The choice of soil reinforcement option depends primarily on its composition, the procedure for determining which is regulated by GOST. Soils, the classification of which was presented above, usually require reinforcement only ifbelong to the non-rock group.
One of the most common amplification methods is thermal. It is used for loess soils and allows strengthening to a depth of about 15 m. In this case, very hot air (600-800 degrees Celsius) is injected into the ground through pipes. Sometimes heat treatment of the soil is done in a different way. Wells are dug into the ground. Then combustible products are burned in them under pressure. Wells are hermetically sealed. After such treatment, the burnt soil acquires the properties of a ceramic body and loses its ability to absorb water and swell.
Cementation
Sandy soil (a 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.
Silicization of soils
On quicksand, dusty sandy and macroporous soils, the silicification method 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 way to amplify. A 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 strengthenedsilicification.
Comparison of replacement and reinforcement costs
Of course, the reinforcement operation will cost less than the complete replacement of the soil. For comparison, let's first calculate how much it will cost to create artificial gravel soil per 1 m23. Selecting land from one cubic meter of area will cost about 7 USD. The cost of crushed stone is 10 USD. for 1 m3. Thus, the replacement of weak soil will cost 7 c.u. for the recess plus 7 c.u. for moving gravel, plus 10 c.u. for the gravel. Total 24 c.u. Strengthening the soil costs 10-12 USD, which is two times 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 to build a house. In the absence of such an opportunity, it is necessary to consider the option of building a building on piles. Strengthening and replacing the soil is carried out only as a last resort. When determining the need for such a procedure, one should be guided by SNiP and GOST. Soils, the classification of which is also determined by the regulations, are strengthened by methods suitable for their specific composition.
