How to determine the foundation: step-by-step instructions

Recommendation points

• Determination of soil type
• Checking the soil for homogeneity
• Determination of the proximity of groundwater
• Determination of the depth of soil freezing
• Calculating the force of soil swelling
• Predicting future subsidence
• Determination of the degree of risk of communal accidents

The construction of any home begins with laying the foundation. The main objective of the zero cycle is to transfer the building load directly to the ground. Therefore, the capital and durability of the building itself directly depends on the reliability and correct choice of the foundation. With the help of the step-by-step instructions for determining the properties of the soil presented in this article, you can independently and without ordering expensive specialist services to determine the type, type and design of the future foundation.

For each specific area and for each type and weight of the building, there is a different type of foundation. For example, it is impossible to equip light pile structures under a massive stone house, and it is not at all advisable to install an expensive huge monolithic slab under a small and light frame bath. That is why, even at the very design stage, it is necessary to unequivocally determine the type of foundation.

The main requirement for a zero cycle at home is reliability, durability and the ability to keep the building perfectly level. And these qualities of the foundation depend not so much on its high cost or massiveness, but on the suitability for a certain type of soil and relief. For example, a solid tape shallow or slab monolithic foundation can simply begin to slide even on a small slope, and a columnar one can “walk” in a clay environment. That is why, before starting construction, and even choosing a site, it is necessary to determine the degree of soil homogeneity, the presence and location of groundwater in it and the depth of its freezing.

Many today order all these geological studies in construction companies. But, if the planned budget is limited, then a lot about the soil can be learned in the so-called “old-fashioned way”.

Determination of soil type

The first step in choosing the type of foundation for a house is to determine the type of soil for the site. For this purpose, you can dig a hole 1.5-2 m deep and see well the so-called “cut” of the earth. The top layer, the darkest one, is soil, and it will need to be removed before starting construction due to unsuitability. But depending on the type of layers below, and you need to select a foundation.

So, the most undemanding soil for the foundation is rocky. It does not settle, erode or swell. To build a foundation, there is no need even for a deepening on it..

Was there sand and clay under the soil, and even with a large admixture of rubble or small stones? This is a gristly soil. It is quite reliable, does not wash out with water, and even a shallow strip foundation can be placed on it.

Strip monolithic reinforced concrete foundation

Prefabricated strip foundation from foundation blocks

Does the soil pass water well, is it compacted and rammed perfectly? This is sandy ground. It will freeze to a shallow depth (up to 1 m), and the foundation in it will not get wet. On such a site, you can even build a strip foundation from separate blocks. Although the columnar “feels” well in such conditions.

From the rain, the earth immediately began to liquefy and erode? This is a clayey soil. The depth of freezing is more than 1.5 m, and the swelling is considerable. Building houses on such soil is the most problematic. Therefore, in this case, it is recommended to give preference to a shallow foundation, which is a rigid reinforced concrete structure perfectly adapted to uneven deformation of the base. These are strip, columnar foundations and a monolithic slab. As a last resort, builders usually still make an anti-heave pillow – they remove the clay and replace it with sand with various impurities.

Columnar prefabricated foundation from foundation blocks

Slab monolithic reinforced concrete foundation

Is there a mixture of sand and clay particles under the soil? The soil will behave accordingly depending on the predominance of one or the second component.

But in place of drained or partially drained bogs there are peat soils. Such land is usually oversaturated with moisture, and the groundwater level is high here. In such a place, the only possible foundation is a monolithic slab, which is also called “floating”. The columnar-transom monolithic foundation also behaves well on slopes and moving soils.

Columnar reinforced concrete foundation in a drilled well

Columnar monolithic reinforced concrete foundation

By the way, for all highly compressible, like peat bogs and sand cushions, heaving and weakly bearing soils, “floating” foundations are ideal. After all, their large surface significantly reduces the pressure on the soil itself, and the stiffeners give sufficient resistance to all kinds of effects of multidirectional loads, which are inevitable during subsidence, freezing and thawing of the earth.

Checking the soil for homogeneity

You can check the soil of the built-up area for homogeneity on your own while drilling a deep well or digging a hole for at least 2.5 m. So the soil cut is clearly visible – with the help of excavation. Thanks to the digging of channels of such depth, you can clearly see what layers the soil itself consists of and which foundation is more suitable for it.

So, if the soil turns out to be extremely heterogeneous, its density is different, and it is noticeable that it is unevenly deformed, then it is better to give preference to this type of foundation as a pile foundation. After all, it is the piles that are able to transfer the pressure from the building to the denser and more stable soil layers – the lower.

Determination of the proximity of groundwater

The presence of nearby underground waters always complicates construction activities. Such soil heaves greatly in winter and subsides in spring, which is extremely difficult to endure even with a good, capital foundation. Often because of this, cracks, breaks appear, and the doors in the house begin to close with difficulty. But it is still half the trouble if the house, together with the soil, rises and falls seasonally at the same time, and much worse if the soil is saturated with waters throughout the entire area. In this case, it is better to carry out the necessary measures, such as drying, draining and re-filling. It is only important not to confuse groundwater and surface water – upstream, which are caused by melting snow and rains and are temporary..

It is possible to determine the level of the groundwater at the site at least approximately independently. To do this, it is necessary to dig shallow wells-pits up to 2.5 meters deep and through them to examine the underlying layers of soil and the presence of groundwater. In addition, it will not be superfluous to refer the liquid itself to laboratory analysis – for harmfulness.

Well drilling

But the full profile of groundwater on the site can only be obtained by contacting one of the modern construction companies for help. In the absence of such an opportunity, it is advisable to consult with neighbors and builders of adjacent houses about the recommended deepening of the foundation. Which, by the way, must be in this case below the level of freezing of the earth.

And finally, the most reliable method for determining the abundance of moisture in the soil is to observe the road around the construction site in spring. So, if the road is asphalted and cracks are visible in it, the soil under it is heterogeneous and rich in groundwater. It will also be useful to observe the basements of old houses in the area – if they are dry and have no cracks, it means that the foundation was built on a strip. And it is desirable to follow this example..

Determination of the depth of soil freezing

In fact, the value of the depth of freezing of the soil is not so important, but whether this value is greater than the distance from the surface of the earth to the first groundwater. Indeed, in winter, such waters quickly freeze, and ice, as you know, expands. And in those places where the location of groundwater is high enough, the earth will rise much higher than in other places. And the built house will rise above one corner, and the second – below. As a result, cracks and early deformations of the foundation.

But, if it is quite difficult to accurately recreate the full profile of the location of groundwater in the ground, and you cannot do without professional analysis, then the depth of soil freezing can be determined independently. To do this, you need to pay attention to:

• soil density. The denser the earth, the more it freezes due to the good conductivity of cold between its individual particles;
• soil moisture. More moist soil freezes deeper. And its saturation with moisture is affected by the level of groundwater and the presence of any natural reservoir nearby;
• the condition of the walls and foundations of neighboring older buildings;
• the amount of snow on the ground in winter. The smaller it is, the deeper the soil freezes in this place..

In addition, in highly freezing soils, and even with high groundwater, today a shallow foundation with thermal insulation is often erected. It is thermal insulation that helps prevent freezing of the ground near the foundation, and, therefore, reduces the effect of frost heaving forces on the building itself. This method is currently considered one of the most effective and economical. In addition, such a foundation is not afraid of changes in soil properties, which inevitably occur over time. The only drawback of shallow foundations is that they cannot be erected on slopes due to a possible shift.

Calculating the force of soil swelling

The depth of laying and the choice of the type of foundation is also influenced by such a circumstance as soil swelling. So, in winter all soils rise to one degree or another, and in spring they sink. The foundation and all the structures located on it “breathe” together with the soil. That is why it is so important that the soil is homogeneous, and due to this, it swells equally throughout the entire site. The top layer of soil – soil – is traditionally removed before construction, because it itself is heterogeneous by nature – it always contains various impurities of organic residues, dissimilar debris, stones and other inclusions, and this is dangerous for the subsequent uneven settlement of the foundation.

The possible strength of seasonal swelling can be determined by the following signs:

• saturation of the soil with moisture. Wet soil always swells more;
• soil composition. Traditionally, clay soils “play” more strongly when compared with sandy ones;
• ground water level. The higher it is, the more the soil will heave..

If on the selected building site the soil swells quite strongly, then it is better to give preference to the slab type of foundation, which is reinforced with an iron frame and in itself is a very reliable structure.

But, if the soil is also soft and deeply freezes, then for lightweight structures, a columnar foundation will also be a good option..

But if the soil on the planned site is not only swollen, but also mobile (most often it is clay-sandy lands), and the groundwater is as close to the surface as possible, the house will be built exclusively on a slab, “floating” foundation.

Predicting future subsidence

The subsidence of the existing soil is also important when choosing a foundation. So, no matter what building is being built, under the influence of its loads, the foundation is necessarily lowered by an amount that is called settlement. If the sediment itself is uneven, cracks cannot be avoided. And the task of the designer is to ensure that in the first two years the building settles as evenly as possible..

The load itself, acting on the base of the foundation, consists of the following components: the weight of the selected building materials, the design features of the attic and interfloor space, roofing material, the roof structure (whether it retains snow on itself or not), as well as operational loads.

Do not forget that all houses that are located close to the building site put pressure on the ground, and the new house will also add its weight.

But if the building site turned out to be with heaving, heavy and subsiding soil, the foundation can only be slab, when the foundation pit under the house is completely filled with concrete. This type of foundation, of course, requires significant costs for metal and concrete, but such a house can safely stand for more than a dozen years, even in a dried swamp. After all, as you know from the physics course, the larger the area of ​​pressure on the surface, the less the pressure force itself.

Determination of the degree of risk of communal accidents

Another important factor in determining the type of future foundation is the risk of accidents in old water pipes. Indeed, even with a slight leak, rusty pipes quickly saturate the surrounding soil with additional moisture, and it swells in cold weather much stronger than usual. And this is dangerous both for the integrity of the foundation and for the building itself. Therefore, it is better to build on the site where the nodes of such systems are located farther, or in extreme cases, install an additional drainage outlet system to reduce the amount of groundwater.

Without exaggeration, ideal is rocky and rocky soil, which, in fact, is a solid stone. Such soil is not afraid of the influence of moisture, frost, or changes in weather conditions – it does not change its properties. In other cases, when designing a house, you need to choose the type of foundation that would match both the planned loads and the natural characteristics of the existing soil of the site..