Foundation pit: calculation and work order

Foundation pit: calculation and work order
Foundation pit: calculation and work order

The shape and dimensions of the foundation pit depend on the features of the foundation and construction technology. Before starting such work, you should ask how to dig a pit for different types of foundations.

Sizing and shape selection

foundation pit

As for the shape of the pit, everything is simple here: the workers will have to dig a hole in the form of a rectangle for the slab base. If we are talking about a tape structure, then the pit should look like a trench. When erecting a columnar foundation, pits or wells are equipped on the site.

Before you dig a foundation pit, you must calculate its depth. It is determined taking into account two factors: the height of groundwater and the level of soil freezing. This implies the need to dig a deep hole, because the sole of the base must be buried in the soil about 30 cm below the freezing line of the soil.

Another parameter, as mentioned above, is the level of groundwater. Helimits the depth of the sole. This suggests that when buried in watery soil, it will be necessary to build a durable waterproofing around the structure, which, however, will increase the cost of construction.

For reference

It is important to make sure that the sole is not closer to groundwater than 0.5 m. When calculating the depth, you need to find a middle ground between these two parameters, which makes it difficult to process on the construction site.

Calculation of length and width


Before you dig a foundation pit, you must determine its length and width. They will depend on the size of the building and the depth of the sole of the structure. Everything is clear with the dimensions of the building: the parameters of the foundation should be 40 cm more than the width and length of the facade (for this you need to add about 20 cm on each side). This requirement is due to the fact that the facade finish should not hang in the void. But the dimensions depend on the depth of occurrence also in the fact that the transverse profile of the pit has the shape of a trapezoid. This is due to the fact that the walls during excavation must have slopes, because these are the rules dictated by safety regulations.

The dimensions of the house, increased by 40 cm, will be projected only on the bottom of the pit, while the upper part should be larger than these dimensions by an amount equal to the depth of the sole of the structure. This allows you to maintain proportions with a 45-degree wall slope, which will protect the walls from crumbling soil.

At zero level, the width and length of the pit will beequal to the length and width of the house, which increase by the depth of the pit. At the level of the base of the foundation, the dimensions of the pit will coincide with the parameters of the facade, increased by 40 cm. If the base is deepened by 0.5 m, this rule can be neglected, while the pit will have vertical walls.

The order of work on the foundation pit for the strip foundation

pit fencing

The construction of a strip foundation involves the construction of a foundation using a monolithic fill. Sometimes brick or block masonry is used. Such technologies involve digging a foundation pit in the form of a trench, which is buried in the soil.

Formwork is installed in the inner part of the space. The external dimensions of the trench increase by 0.4 m in relation to the width and length of the house itself. The width of the trench is calculated taking into account the width of the walls, to which 0.5 m is added for the gap for the installation of the formwork. The minimum belt width is 400mm and the minimum trench width is 1m.

Before you dig a foundation pit, you need to outline the dimensions of the hole in the ground at the construction site. Before erecting a strip foundation, 30 cm of a layer of fertile soil should be removed from the site. This will not only straighten the relief of the site, but also save builders from problems with soil organic matter. It is necessary to start digging a trench from the highest angle. You should go deep into the ground along the entire perimeter.

When digging, manual labor or heavy equipment like an excavator is used. The depth of the pit must be controlled withwith the help of milestones that are immersed in the corners of the trenches, they form a profile. If the walls of the pit in the form of a trench will deepen by more than 0.5 m, then they should be strengthened with shields, which will be held by stakes from below, and from above - by struts that are installed in the form of crossbars. After the formwork is installed, these spacers are removed.

When digging a foundation pit, part of the extracted soil is stored away from the edge of the trench. This is especially true for the sand component. It should not be left closer than 7 m from the pit. You can use the excavated soil for backfilling and drainage. However, the rest of the soil mass will have to be disposed of, you can spend it on a landscape device.

Pit for slab construction

foundation pit

When excavating a pit where a slab base will be laid, it is necessary to prepare a rectangular pit, but this should be done according to other rules. The dimensions of the pit will be equal to the length and width of the facade of the building. But this is true only for shallow construction. Otherwise, the height of the foundation should be added to the length of the facade.

Development should be carried out in steps, gradually removing 0.5 m of the soil layer. The dimensions of each step should be 0.5 m smaller than the previous one. In the process of digging, steps will be formed on the walls, the height of which is 0.5 m. As for their width, it is 25 cm. Earthworks do not involve the use of manual labor, since it's impossible.You will have to order heavy equipment in advance:

  • dump trucks;
  • bulldozers;
  • excavators.

Work methodology

excavation calculation

The process of arranging a pit for a slab structure itself is as follows: at the first stage, 30 cm of fertile soil is removed from the construction site. This must be done at the location of the future base. This requirement is due to the fact that rotten organic matter can degrade the performance of the foundation. On a flat and cleaned surface, it is necessary to apply the zero dimensions of the pit, this should include the length and width. Along these boundaries, it is necessary to carry out the first excavation, which will be deepened into the soil by 0.5 m.

It is necessary to remove the soil from the central part of the pit, gradually moving towards the edges of the construction site. Once the first layer is developed, you can move on to the second. Its borders should be laid in the dimensions of the first layer and reduced by 25 cm. These actions should be continued until you reach the bottom of the pit, which is the platform for pouring the sole.

The extracted soil is sorted into two parts. The first is sandy soil, which is located at the boundaries of the pit and will be used for backfilling. The second part must be taken out of the site.

Pit for column base

snip pit

When the calculation of the pit is carried out according to the above scheme, you can proceed to earthworks. For a columnar base,prepare shallow trenches up to 0.5 m. They will be opened along the boundaries of the facade of the future building. At the bottom of the trench, special recesses in the form of pits should be made. They are needed to install intermediate and corner posts.

Recommendations from a work specialist

excavation depth

From the site, as in the cases described above, it is necessary to remove the fertile soil layer, deepening by 30 cm. A trench of 0.5 m must be dug along the placed edges. The minimum width should be 70 cm. The maximum value is 100 cm. In this case, you should also be interested in the depth of the pit. It will be 0.5 m for the pits. Their dimensions are 0.5 x 0.5 m. They are carried out at the bottom of the trench from the corners. The distance between the supports will be 2 m maximum. The minimum value is 1.5 m.

The sole will be poured into the pits for future supports. The depth of the pit is determined by milestones. The soil that has been worked out is placed inside the perimeter of the trenches, it will be used to fill the internal sinuses. If you arrange a pile foundation, then a pit is not needed. Piles are installed in wells that are pre-drilled with a manual or mechanical tool. The peculiarity of this process is expressed in the undeniable technological advantages of this blade.

Sanitary norms and rules

If you started building a house, then first you have to dig a foundation pit. SNiP for this must be observed. After reviewing them, you can understand that the foundation pit is needed to fill the stabilizing pad and positionstructures below ground level. Usually the strength of the soil is not enough. Sometimes groundwater is too high in the territory. But in any case, the technology of creating a pillow is not accompanied by complexity, and the benefits are very significant.

SNiP 3.02.01-87 states that it is almost impossible to develop soil in winter, and mechanical development will not go well. Soil transportation and removal will be complicated. If you plan to carry out work in the winter, then all processes will be slowed down. The time spent can be doubled, due to the duration of the excavation.

Base Guard Technology

In order to avoid serious consequences, pit fencing is often used. To do this, the technology of mounting tongues is used. This localizes subsidence of the soil and excludes its characteristic changes. They occur only in the field of construction work. Other buildings with such a fence are protected from damage and deformation.

The technique is to install piles that are made from different materials. They are next to each other. The pit can be fixed with the help of supports in the form of temporary fences. This applies to wooden piles, which eventually lose their integrity, so they are rarely used. Increasingly, builders are opting for metal sheet piles that can be reused.

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