Good day dear readers!
Foundation is the foundation of your home. What you make the foundation, so will your house. If you do not correctly calculate the foundation for the house, then, accordingly, it will not stand for a long time.
In this article you will find the necessary information about the foundations:
How to do it right foundation for a house,
How deep to lay it
What load can the foundation of the building withstand and much more.
YOU WILL FIND A VIDEO ON THIS TOPIC AT THE END OF THE ARTICLE.
The most common foundations are strip, columnar, slab and their derivatives.
The purpose of any foundation - withstand the load from the building or structure, distribute it and transfer the load to the base (soil).
If the soil does not withstand the load from the building (marshland), then before starting the construction of the foundation, you can make a partial replacement of the soil with a more durable one, for example, cover it with granular slag (which eventually turns into concrete), or use piles.
The choice of one or another foundation mainly depends on the type of soil and on the depth of groundwater.
Foundation sole - this is the lower plane of the foundation, which rests on the ground.
Foundation depth - is defined as the distance from the surface of the earth (soil) to the base of the foundation. Basically, the depth of the foundation depends on two factors: the level of groundwater and the depth of soil freezing.
If all the nuances and subtleties are taken into account when laying the foundation, then this will affect the durability of the higher building!
Remember that the cost of laying the foundation is from 15 to 25% or more, depending on the type of soil, its freezing and the depth of groundwater.
If you save on the foundation in the wrong place, then reworking it and eliminating errors will be very expensive, and in some cases (as practice shows) it is impossible!
1) Preparatory work. Foundation layout.
We are preparing the site in the place where the future house will stand. We clear the area of bushes, trees. If the top layer consists of good fertile soil, then it can be removed and transferred to a place where it will not interfere.
It is advisable to divert surface water (precipitation) to the side so that the construction site is not flooded.
The layout of the foundation begins with a breakdown of the plan of the house in kind. The project (on the master plan) usually indicates what the house needs to be tied to. Most often, the house is tied to the road or to neighboring buildings.
First of all, we mark out where the outer walls of the house will be. For marking, it is best to use wooden or metal pegs and a nylon cord.
So: we mark the contour of the building and hammer pegs in the corners.
Then it is necessary to make a cast-off around the future building. Scraps make it incredibly easy to build in the early stages! If you do not want to put it, then you can not put it, you will still do everything right. But, as practice shows, the cast-off significantly saves time during the further laying of the foundation and the construction of the basement.
shabby- these are two pegs to which a board is nailed with an edge.
For convenience, we hammer the cast-off at a distance from the edge of the future pit, at a distance of 2 to 5 m. In such a way that the cast-off does not interfere with the operation of heavy equipment:
An excavator that will dig a pit,
Mounting crane, which will mount foundation blocks and slabs.
Normal entrance of the mixer and the like.
Sometimes a cast-off is made continuous - around the entire perimeter of the house, but this is not very convenient. The best option is to make a cast-off from small elements similar to a small bench.
The cast-off is usually placed in such a way that all axes can be marked on it.
Cast-off height- most often we do 500 - 600 mm above the ground. You can make it higher, for example, 100 - 150 mm higher than the future floor of the first floor.
Some neglect the axes and use the edges of the outer walls of the building (or main walls) as a basis. I do not recommend doing this, as it is easy to make a mistake.
If you mark everything from AXIS, you will never go wrong.
When the axes intersect, a right angle (90 degrees) is formed. If you neglect the right angle, you get a crooked house. This will come out when installing the roof and floors. Visually, you can see that the house was not built evenly (without a right angle), first of all it can be seen on the roof of the house!
How to make an easy right angle- to check the angles, you can use the "Egyptian triangle". From the intersection of the axes we set aside 3 m in one direction and in the other direction from the intersection of the axes (perpendicularly) we lay 4 m (you can tie a knot or a piece of wire). After that, the first and last knots are connected with a tape measure, you should get 5 m (the square of the hypotenuse).
If it is difficult to check a right angle, then the best option is to measure the diagonals. The diagonals must be the same size.
Site layout- it is desirable to “shoot” the site with a level and find out the lowest and highest points (site layout) and take one of the marks as the original one. Thanks to the layout of the site, you will know where you need to dig more and where you need to dig less.
If there is no level, then you can use the usual hydro level (thin, transparent hose filled with water). We make a mark on the cast-off board with a pencil (or hammer in a nail) and transfer this mark with the help of a hydraulic level to other cast-offs. The result is a horizontal plane around the perimeter from which you can measure the depth of the pit or trench.
When we measure the depth of the pit (or trench) from the horizontal plane, then the pit itself below will have a flat (horizontal) surface. In other words, the bottom of the pit will be flat.
So: from the axes we set aside in parallel on both sides the edges of the future foundation. We stretch two nylon cords along the edges of the foundation and transfer it to the ground using ordinary sand. That is, we sprinkle sand with our hands directly on the nylon cord and on the ground (on the ground) a contour of the outer and inner edges of the foundation looms.
Then we wind the nylon cords so that they do not interfere with digging.
The cast-offs are completely removed only after the builders have built the basement of the house.
2) Earthworks.
Ditches (trenches) are most often dug with an excavator. The shape of the pit (trench) depends on the type of soil and its depth. In dense, not loose, soils, the walls of the trenches are usually vertical (if the trenches are not deep and the groundwater is far from the base of the foundation) and they are used instead of formwork.
Figure 3.1 Tape and column foundations, in heaving soils.
1- inclined walls of rubble masonry; 2 - laying of backing bricks; 3 - core made of reinforced concrete; 4 - concrete; 5 - future base; 6 - backfilling with soil; 7 - reinforced concrete slab, base; 8 - concrete slab; 9 - fittings; U.P.G.- the level of soil freezing.
When erecting buildings and structures on a steeply dipping terrain, it is necessary to take into account the possible shift, lateral soil pressure. The magnitude of the lateral soil pressure depends on many factors (type of soil, how steep the slope is, etc.) and therefore it is quite difficult to calculate it.
The most reliable foundation on a steeply dipping terrain is a strip foundation, because it is rigidly connected to each other in the transverse and longitudinal directions.
A columnar foundation on a steeply dipping terrain must be rigidly tied on top. For communication, it is better to use a reinforced concrete monolithic belt, then all the structural elements of the foundation will work as a whole.
To determine the depth of the foundation, you need to know three main indicators:
1) The level of soil freezing.
2) The height of groundwater.
3) The composition (type) of the bearing soil on which the foundation of the house (building, structure) will be located.
If in winter the groundwater is more than 2 m below the freezing level of the soil, then for many soils (fine and silty sands, hard clay soils), the depth of the foundation is calculated without taking into account the level of soil freezing.
In other words, the groundwater level is far from the level of soil freezing (more than 2 m), respectively, the soil is relatively dry and will not heave. This will greatly reduce the cost of building a foundation!
And if the groundwater is close to the level of soil freezing (up to 2 m), then the soil (clay soils, fine and dusty sands) is saturated with water and will swell in frost. Therefore, when groundwater is close, the soil is wet. The foundation must be laid taking into account the freezing of the soil, that is, the base of the foundation must be not higher (preferably a little below) the level of soil freezing.
Minimum foundation depth.
The minimum depth of the foundation footing in dry soils (fine and coarse sands, hard clays) is 0.7 m.
The minimum depth of the foundation footing in wet soils (fine and silty sands, plastic clay soils, subsiding loess loams) is 1.2 m.
Minimum foundation footing depth for a house that has a basement. The sole of the foundation is laid below the floor level in the basement by at least - 0.4 m.
Table 3.1 How deep should the foundation be laid?
| No. p / p | Bearing soils within the freezing depth. | The distance from the depth of soil freezing to the level of groundwater. | The depth of the foundation sole for the construction of one-story and two-story buildings. |
| Rocky and semi-rocky soils | Irrelevant. | It does not matter, does not depend on the depth of soil freezing | |
| Coarse and medium sands, gravelly sands, coarse-grained soils. | Irrelevant. | ||
| Silty and fine sands, clays (wet when freezing become heaving soils), loams, sandy loams. | More than 2 m. | It does not depend on the depth of soil freezing, but not less than 0.5 m. | |
| Less than 2 m. | Not less than 3/4 of the depth of soil freezing, but not less than 0.7 m. | ||
| The groundwater level is above the ground freezing level. | Not less than the depth of soil freezing. |
To determine the level of soil freezing in your area, you can use the map (see below).
Figure 2.2. Depth of soil freezing in centimeters.
How to independently determine the level of groundwater and soil composition.
Determining the level of groundwater is quite simple: it is necessary to dig a pit - a well on the construction site (on which the future house will stand). The size of the well is approximately 1 meter by 1 meter and a depth of about 2.5 -3 m.
The pit-well must be protected from the flow of surface water and precipitation into it. The most reliable information about the groundwater level, you can get in the fall or spring, when the groundwater level is highest.
To reduce the cost of digging a hole, you can dig it, for example, in the place where the basement will be.
Thanks to the pit-well, you will find out not only the level of groundwater, but also the composition of the soil.
Often upper layer- this is a fertile layer, it is usually removed, since it does not settle evenly due to decay of organic residues (plants, roots) and the house may burst. The fertile layer is easy to recognize, as it is darker. The thickness of the fertile layer is from 100 to 1000 mm or more.
Beneath the fertile top layer is the natural underlying soil. This soil (natural underlying) is bearing and perceives the load from the base of the foundation and the building above.
medium and coarse sands, gravelly, then this is a reliable foundation for your home. The minimum foundation depth in such soils is 0.5 m.
If the natural underlying soils - silty and fine sands, sandy loams, clays, loams, groundwater level must be taken into account. With a high level of groundwater, these soils have a reduced bearing capacity.
If the natural underlying soils - loess loams, then at low humidity they can take quite large loads. With a high level of groundwater, loess-like loams can sag even from their own weight. How to distinguish this not very reliable soil from others?
Quite simply - it must be lowered into the water. Unlike ordinary clay soils, loess-like loam disintegrates much faster in water.
4) How to calculate the width of the base of the foundation.
All soils can take the load from a higher-standing private residential building (except for silts and peat bogs). Individual houses are relatively small in size and weight.
If the bearing capacity of the soil is weak, then it is necessary to increase the area of the base of the foundation to reduce the pressure on the soil. The larger the area of the base of the foundation, the less pressure on the soil.
b) Type of bearing soil All soils are different and have different bearing capacity. When you know the type of soil on which your future house will stand, you can determine the bearing capacity of this soil by table 4.1(see below).
For example, stony soils have the highest bearing capacity: 5.0 - 6.0 kg/cm2, and plastic clays have a weak bearing capacity: 1.0 - 3.0 kg/cm2.
Table 4.1 Design resistancesgruentovand theminides.
| No. p / p | Soil types | kPa | kg/cm2 |
| 1 | Coarse clastic soils, crushed stone, gravel | 500 – 600 | 5,0 – 6,0 |
| 2 | The sands are gravelly and coarse | 350 – 450 | 3,5 – 4,5 |
| 3 | Sands of medium size | 250 – 350 | 2,5 – 3,5 |
| 4 | The sands are fine and silty dense | 200 – 300 | 2,0 – 3,0 |
| 5 | Fine and silty sands of medium density | 100 – 200 | 1,0 – 2,0 |
| 6 | Sandy loam hard and plastic | 200 – 300 | 2,0 – 3,0 |
| 7 | Loams are hard and plastic | 100 – 300 | 1,0 – 3,0 |
| 8 | Clay hard | 300 – 600 | 3,0 – 6,0 |
| 9 | Plastic clays | 100 – 300 | 1,0 – 3,0 |
So: when the total weight of the building is known and what load the soil can take (per square centimeter), we calculate the area of \u200b\u200bthe sole of the foundation.
Everything is done very simply and for clarity, let's look at an example - how to determine the width of the base of the foundation (the area of the base of the foundation) for a two-story residential building.
Example:
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