Let's consider the forces which act on a foundation in summer and winter time, taking into account the most adverse conditions which influence on the foundation. Foundation which is located on heaving soils with high water level, placed above the level of soil freezing.
Only two forces act on a foundation in summer. They are:
structure load on the ''A'' foundation;
force resistance of ''B'' soil.
As the soil freezing in winter time, a scheme of the forces, acting on the foundation in winter, changes dramatically.
First, the soil freezes in the upper part of the foundation and the forces identified by the subscript "C" start to squeeze it from both sides.
As the soil freezing, an effect of these forces increases and their tangential component tends to push the foundation of the foundation pit.
By the time of soil freezing at the depth of frost penetration level, forces "B" begin to act on the foundation.
The combined effect of the forces C and D inevitably leads to the foundation rising in the "A" value.
As was noted above, the value of the "A" foundation lifting and the foundation returning in its place is not the same for all sections of the foundation after the thawing of this ground.
These are the causes of a deformation of any foundation, which lead to the unpleasant consequences, and these consequences could be very serious, up to the cracks in the wall brick masonry of a house.
Such foundation structure should be attributed to incorrect.
The following figure is the chart of forces for deep foundations, the underside of which is situated below the level of soil freezing. It is the wisest decision.
Taking this decision the foundation underside does not feel a pressure of frozen soil, it means that the impact of "B" strengths. And if there are no swelling forces, there is no winter foundation ascent on the "A" value by such forces.
Naturally, the penetration of the foundation leads to a slight increase of "C" type forces, but their impact on the foundation is lower than the impact of B forces.
To neutralize the action of these forces or reduce their exposure to a minimum are recommended:
produce the reinforced concrete foundation only;
foundation base should be broadened, in the form of a support point;
vertical walls should be narrowed to the top of the foundation;
side face of a foundation should be covered by a sliding layer (polyethylene, waste oil, pads of two roofing material layers, sand mat, etc.).
Types of foundations
A foundation is made of a concrete or a concrete in a combination with a brickwork or stone masonry. According to the way of pressure on the ground, all foundations are divided into: strip foundations, post foundations (piles) and panel-wall foundation.
Strip
Strip foundation is the foundation which has the same cross-sectional shape across walls perimeter of a building (including under all its internal load-bearing walls). Such foundations scaffold under heavy buildings. They are rarely used in the heaving and deep freezing soils.
Post (piles)
Post or piles foundations are the most common and cheapest type of foundations for buildings with lightweight walls. The construction of such foundations costs 1.5-2 times cheaper than strip ones. The main element of such foundations is a post (pile). The post can be made from wood, stone, brick, concrete and reinforced concrete. It could also be an asbestos pipe, which is used as a form and is filled with a concrete mix.
Panel-wall foundation
Panel-wall foundations are usually constructed on the heavy swelling and subsiding soils. They have a rigid construction. It means that one panel, carried out under the whole plane of the building. Such foundations align all vertical and horizontal movement of a soil and they have already received another designation that is floating. The construction of panel-wall foundations is practiced mostly in low-rise building with a small and simple form of building plan. They are quite expensive due to a large volume of concrete and metal expenditure for armature.
If you are going to lay a foundation…
Lately we can see a large quantity of different translated literature, the translation of which is made automatically, without of any technical wording or the connection of construction recommendations to the Russian conditions.
In some of these publications is stated that to build a house or a cottage it is enough just to lay a foundation to the depth of 50-100 cm.
We should not follow such advices, because for most countries of Western Europe the subzero temperatures of 12-15 degrees is an extremely rare event.
In conditions of such mild climate, compared to ours, the depths of soil freezing are almost never formed reaching or exceeding the level of underground waters, and therefore the problem of winter soil heaving is just not worth it.
In these countries it is possible to lay a light-weight foundation, which gives a significant reduction in total cost of their construction. The construction of the same foundation with a small depth is a gross error for the Russian climatic zones of the central belt. If you want to build a house by yourself or you are laying a house foundation on the basis of such recommendations from such sources, the troubles are guaranteed. Use the literature by Russian authors or the literature checked with help of technical wording.
Fencing foundation
Foundation is the base of a building and the more it is stronger, the more durable is the structure.
The cost of foundation is about 15-20% of the total fencing cost. Correction of improperly foundation is technically challenging and the costs of these works can achieve 50% of the total fencing cost. Therefore, the choice of foundation must be done very responsibility.
The main reason of an instability, deformation or destruction of a foundation of certain soil types during the winter freezing is the action of frost heave forces (non-uniform uplift, "swelling"). Such behavior of soils is closely related to the depth of soil freezing in the construction area and the depth of underground waters.
It should be kept in mind that the power of heaving is so strong that it is able to lift almost any building construction. According to some studies, this force reaches 10-15 t/m2. If the foundation area is 10 m2 the heaving force is 100-150. It is impossible to control these fantastic forces, so there is only one solution that is to make the competent performance of your foundation.
So, before you are going to lay a foundation you need to know:
the type of ground on which fencing will be constructed;
the depth of freezing in the construction area;
the level of groundwater.
Types of soils
Main types of soils are described below. Particular attention of heaving nature is paid to the behavior of soils in winter time.
Rocky
Rocky grounds are the most reliable. They are durable, do not subside, wash away or swell. Foundation could be built directly on the surface of such soil, without of any opening or penetration.
Cartilaginous
This type of soil contains gravel streaks and fragments of stone. It does not compressed and does not wash away. In this case we recommend the laying of your foundation at the minimum depth of 1,5 m.
Sandy
Sandy soils tend to packing under the pressure, in other words to subsiding. These soils do not entrap water and freeze slightly. We recommend the laying of your foundation at the depth of 40 to 70 cm.
Loamy
Loamy are the ground which occupy an intermediate position between the sandy and the clayey soils. They contain from 3 to 30% inclusions of clay. When a soil contents from 10 to 30% of clay it is attributed to the loamy, and at a low content of clay to sandy loam.
Clayey
Clayey soils can shrink, wash away and heave when it is cold. It is the worst ground for a foundation construction, which in this case should be laid at all depth of frost penetration.
Groundwater level
The level of underground and groundwater has a significant influence on the soil behavior. The conditions under which the depth of frost penetration is less than the depth of groundwater are better for the future foundation. Conversely, the conditions when the depth of frost penetration is bigger than the depth of groundwater are more destructive.
In the last case the depth of soil freezing increases with the frost increasing. When the depth of frost penetration reaches the level of underground waters, they begin their transformation into the ice, and together with it the soil swelling begins.
Also this unpleasant phenomenon is overshadowed by the fact that this swelling process is almost never uniform, and in different parts of the foundation soil upgrade will be uneven. The consequences are skewing of foundation, redistribution of loads in it and around the structure, possibility of cracking in the very foundation and the walls of the house.
If the process were uniform, we should not have to pay so much attention to the swelling problem, as in winter home is uniformly raised and in spring is evenly lowered. Unfortunately, it is also not achievable because of other reasons.
Therefore, if the groundwater level is high and these waters are captured by the depth of freezing, there are two outs of such situation:
consider this factor when you are going to choose the reliable version of your foundation and don't pay much attention to the increasing of construction estimate;
if it is possible, carry out all works to guarantee the lowering of ground waters (drainage, construction of drainage channels, etc.).
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