The term "soil swelling" hides a rather complex phenomenon of natural origin, which can lead to serious consequences. At that time, when the earth freezes, the foundation, together with the entire structure, rises. When thawing, the opposite happens - the base drops. But the bottom line is that this happens unevenly.
As a result, buildings come into emergency and sometimes threatening condition. In some cases, due to such a phenomenon, buildings begin to completely collapse, and completely.
Feature of the natural phenomenon
The main feature of the heaving process is a significant increase in the volume of water in the soil due to winter freezing. According to GOST 25100-2011, 5 categories are distinguished, which differ among themselves in the degree of heaving (the level of soil expansion is indicated in parentheses):
- Excessively heaving soils - more than 12%.
- Strongly soiled soils - not more than 12%.
- Medium-grained soils - up to 8%.
- Loosely soiled soils - approximately 4%.
- Non-porous soils - does not exceed 4%.
However, the latter category should be considered conditional, because in nature there simply does not exist soil where moisture is completely absent. Only granite and coarse soil rocks should be attributed to this type. However, in our conditions, this kind of soil is quite rare.
Threatening stages
The territory of the Russian Federation runs throughout the northern part of the Eurasian continent. For this reason, in winter there is always minus temperature. Depending on the specific region, the soil may be frozen for a period of 2 to 9 months.
In this case, several stages of heaving of the soil can be distinguished:
- I - preliminary. In this case, the soil is cooled to a temperature that is not yet equal for water crystallization.
- II - based. In this case, the water is already beginning to transform into its other state of aggregation, turning into ice. Accordingly, its volume expansion takes place, which, as we know, does not bode well.
- III - hypothermia. Here, under the influence of frost, the soil is compressed. Subsequently, this leads to a sharp decrease in temperature.
It is only worth considering that the listed states are conditional in nature, since the transition from one stage to another is very slow. At the same time, one more step can be distinguished in the process of thawing soil - its subsidence.
As a rule, the phenomenon of heaving is observed mainly in the winter. For this reason, this season is not suitable for construction, especially on a massive scale. This is due to serious danger - the risk is very high that the erected structure will be destroyed very quickly.
In particular, the strength of soil heaving should be considered by those who live in the Far North. In this area, the lower soil layers freeze much more than in other latitudes.
The main trigger factor
At first glance it seems that the damage from heaving may not be so huge, but it only seems. To realize the whole threat from such a natural phenomenon, it is worthwhile to clearly understand how this process occurs.
As we now know, the phenomenon is characterized by heterogeneity, which is mainly due to the difference in the height of the earth's surface. As a rule, this is observed in the spring - that side of the building, which is located in the south, is well heated. In addition, spring drops make their contribution. With the onset of evening, a large amount of melt water accumulates in the ground, which then becomes ice.
The mass of this layer can reach several centners, and this is already enough to raise the foundation to a certain height. This process takes all night.
In the afternoon, the opposite picture is observed - with increasing temperature, the ice in the earth begins to thaw. Accordingly, the base begins to sag, and along with this, the earth is again enriched with another portion of water, which then crystallizes again. All this happens every day until the temperature regime is normalized.
During the spring period of the water level difference, the building can drop a few centimeters. This is quite enough to cause serious damage, which will subsequently be very difficult to fix, if at all it can be done.
Other causes of soil heaving
Various factors can influence the heaving intensity, among which we can mention the following:
- The duration of the winter period and its intensity (severity).
- The thickness of the snow.
- Soil characteristics.
- Rainfall per season.
- Humidity level.
- The nature of the terrain.
- Vegetation.
- The depth of groundwater.
- The location of the area in relation to the south side.
Since buildings can receive very serious damage from heaving, the construction of its foundation should be carried out below the freezing depth of the soil. This value is directly dependent on the area where the construction of houses is planned.
It is worth noting that the Mediterranean soil moisture is a fundamental factor that has a greater effect on heaving intensity. At the same time, one should not discount the density of the lower layers of the soil. But much also depends on this parameter.
The denser the soil, the less deformation the building will undergo. Otherwise, frost heap will be more intense, which does not bode well.
How to determine the degree of soil heaving?
For this, it is worth considering not only the composition of the soil, but also the level of groundwater. Any owner of suburban real estate may be faced with the need to determine how strong the heaving soil is in the area of a private site. To achieve this goal, it is necessary to dig a pit up to 2 meters deep. This is such a special vertical development of a square, round or rectangular cross-sectional shape.
After this, wait a few days. If moisture did not appear at the bottom of a dug small pit, you need to drill another 1.5 meters. One has only to seem water, the process can be stopped. Now it remains to measure the distance from the water level to the surface.
You can determine the type of soil by visual inspection. Based on these data, an approximate conclusion can be made regarding the degree of expansion of the soil during the cold season.
We turn to mathematical calculations
Calculation of soil heaving can be done independently, using the formula E = (Hh) / h, where:
- E is the coefficient of the degree of heaving of the soil.
- H is the height of the soil after freezing.
- h is the height of the soil before freezing.
Accordingly, you must first perform the necessary measurements. And not only in the summer, but also in the winter. To draw conclusions regarding the heaving of the soil can be based on changes in height. If this parameter is 10 mm or more per 1 meter of freezing, then the coefficient E will be 0.01, which already indicates that appropriate measures should be taken to avoid serious consequences.
It is worth recalling once again that soil, in which there is a high level of moisture, is predominantly affected by heaving processes. Turning to ice, it expands markedly, increasing in volume. Who did not freeze water in a plastic bottle by placing it in the freezer of the refrigerator for experimental purposes or as needed? You can immediately imagine all the power of the water element, collected in a limited volume.
Clay rocks of the soil, loams and sandy loam are more prone to heaving. And clay, due to the presence of many pores, is able to retain water well.
Ways to minimize damage
Now it is clear to us that the amount of soil heaving should not be underestimated. But how to avoid unpleasant consequences that can pose a serious threat to people's lives? There are several ways to do this. But since the heap of the soil is largely related to the impact on the foundation, most of them imply ways to strengthen or isolate it. Consider the best options for solving such a difficult problem.
Soil replacement procedure
This method works only when laying the foundation - a sand cushion is placed under the base. Moreover, it should be noticeably wider than the very foundation of the building. Then it is well rammed and compacted. Thanks to such a pillow, an even distribution of the entire load on the base is ensured. In addition, the layer of heaving soil decreases, therefore, the strength of the natural phenomenon also becomes weaker. In addition, the sand cushion has cushioning properties.
In addition, experts recommend, in order to avoid deformation from heaving of the soil, to fill with non-porous soil the area between the formwork after its removal and the soil. Such a measure will avoid freezing the soil to the walls of the foundation.
Only after some time the sand in the backfill (including the pillow) can mix with clay particles, losing its non-porous properties. To avoid this, the sand cushion and backfill should be separated by a film, ruberoid or filter cloth.
Foundation construction
Here we have in mind the optimal choice of the type of foundation, which is relevant only at the stage of building a house. If it has already been erected, then another method of solving the problem should be used. Regarding this technique, you can choose between two types of foundation - a slab structure or a pile foundation.
Monolith
The formation of the slab structure will make the building heavier, which, in turn, will minimize the impact of soil on the foundation. Of course, it will not be possible to completely exclude the influence of frost heaving on a monolithic plate with a height of more than 200 mm, recessed into the ground. At the same time, as a result of soil heaving, the base will simply rise evenly to a small height in winter. With warming, the foundation will return to its original position.
From a technical point of view, the implementation of a slab foundation is simple. Certain difficulties usually arise during the reinforcement operation. In addition, this method is quite costly.
Piles
The device of the pile foundation will do with little blood. Only such a design is applicable only to buildings with low weight (construction using frame technology, the use of sip panels, etc.).
For the foundation, such options may be suitable:
- Screw piles - they are screwed into the ground slightly below its freezing level.
- Reinforced structures - first you need to prepare several wells, and then install the rods in them, wrapped in roofing material and wrapped in a metal frame.
After the piles are installed, they should be connected with special beams or plates to evenly distribute the load on the foundation.
House perimeter insulation
This method allows to minimize or completely eliminate freezing of the soil. Due to the warming of the soil, it is possible to erect a shallow base due to a decrease in the depth of freezing.
Only this option of combating soil heaving is relevant for areas with a positive average annual temperature. The width of the laid insulation should be equal to the depth of freezing of the soil. As for the thickness of the material, it all depends on the insulating properties and the nature of the climate.