The shape and dimensions of the foundation pit for pouring the foundation depend on the features of the foundation and construction technology. Before starting such work, you should ask how to dig a foundation pit for different types of foundations.
Sizing and shape selection
As for the shape of the pit, then everything is simple: the workers have to dig a hole in the form of a rectangle for a slab base. If it is a tape design, then the foundation pit should have the form of a trench. During the erection of a columnar foundation, pits or wells are arranged on the site.
Before digging a foundation pit, you must calculate its depth. It is determined taking into account two factors: the height of the groundwater and the level of freezing of the soil. This implies the need to dig a deep hole, because the sole of the base should be buried in the soil about 30 cm below the freezing line of the soil.
Another parameter, as mentioned above, is the groundwater level. It limits the depth of the sole. This suggests that when buried in watery soil, it will be necessary to build a durable hydraulic protection around the structure, which, however, will increase the cost of construction.
For reference
It is important to make sure that the sole is not located closer to groundwater than 0.5 m. When calculating the depth, it is necessary to find a middle ground between these two parameters, which complicates the process at 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. With the dimensions of the building, everything is clear: the foundation parameters should be 40 cm more than the width and length of the facade (for this it is necessary to add about 20 cm on each side). This requirement is due to the fact that the facade finish should not hang in a void. But the dimensions also depend on the occurrence depth in that the transverse profile of the pit has the shape of a trapezoid. This is due to the fact that the walls must have slopes during excavation, because these are the rules that dictate safety.
The dimensions of the house, increased by 40 cm, will be projected only to the bottom of the pit, while the upper part should be larger than these sizes by an amount equal to the depth of the sole of the structure. This allows you to ensure proportions with a 45-degree slope of the walls, which will protect the walls from shedding soil.
At zero level, the width and length of the pit will be equal to the length and width of the house, which increase to the depth of the pit. At the level of the base of the foundation, the dimensions of the pit will coincide with the facade parameters increased by 40 cm. When the sole is deepened by 0.5 m, this rule can be neglected, while the foundation pit will have vertical walls.
The order of work on the pit for the tape base
The construction of a strip foundation provides for the construction of a foundation using monolithic casting. Sometimes brick or block masonry is used. Such technologies involve digging a foundation pit in the form of a trench that is buried in the soil.
Formwork is installed in the interior 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 to the clearance for the installation of formwork. The minimum width of the tape is 400 mm, and the minimum width of the trench is 1 m.
Before you dig a foundation pit, you need to outline the dimensions of the pit on the ground at the construction site. Before the construction of the strip foundation, 30 cm of the 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. The soil should be deepened around the perimeter.
When digging, manual labor or heavy equipment like an excavator is used. The depth of the pit must be controlled with the help of milestones that are immersed in the angular conjugation 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 that will be held by stakes from below and from above by spacers that are installed in the form of crossbars. After installing the formwork, these spacers are removed.
When digging a pit under the foundation, part of the extracted soil is stored at a distance from the edge of the trench. This is especially true for the sand component. Do not leave it closer than 7 meters from the pit. You can use the excavated soil with backfill and drainage. However, the remaining soil masses will have to be disposed of, you can spend them on a landscape device.
Foundation pit
Carrying out excavation work on the pit, where the slab base will be arranged, it is necessary to prepare a rectangular pit, however, it should be followed by other rules. The dimensions of the pit will be equal to the length and width of the front of the building. But this is only true with shallow construction. Otherwise, the height of the foundation should be added to the length of the facade.
The development should be carried out in steps, gradually removing 0.5 m of the soil layer. The dimensions of each step should be less than the previous one by 0.5 m. During digging, steps will be formed on the walls, the height of which is 0.5 m. As for their width, it is 25 cm. Earthwork does not involve the use of manual labor, since it is impossible. You will have to order heavy equipment in advance:
- dump trucks;
- bulldozers;
- excavators.
Methodology
The process of constructing a foundation pit for a slab structure 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 foundation. This requirement is due to the fact that decayed organic matter can degrade the performance of the foundation. On a flat and cleaned surface, it is necessary to apply zero dimensions of the pit, here should include length and width. At these boundaries, it is necessary to carry out the first excavation, which will be buried in 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 boundaries should be laid in the dimensions of the first layer and reduced by 25 cm. These steps should be continued until you reach the bottom of the foundation pit, which is the platform for filling the sole.
The extracted soil is sorted into two parts. The first is sandy soil, which is located at the borders of the pit and will be used for backfilling. The second part must be taken out of the site.
Foundation pit
When the calculation of the pit is carried out according to the above scheme, you can proceed to earthwork. Shallow trenches up to 0.5 m should be prepared for the columnar base. They will be open along the boundaries of the facade of the future building. At the bottom of the trench, special excavations in the form of pits should be made. They are necessary for the installation of intermediate and corner posts.
Recommendations of a specialist
From the site, as in the above cases, you should remove the fertile soil layer, deepening by 30 cm. On the placed edges, you need to dig a trench by 0.5 m. The minimum width should be 70 cm. The maximum value is 100 cm. In this case, you too should be interested in the depth of the pit. It will be 0.5 m for 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.
Soles under future supports will be poured into the pits. 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 add internal sinuses. If you arrange a pile foundation, then the foundation 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 foundation.
Sanitary regulations
If you started building a house, then first you have to dig a pit. SNiP for this must be observed. Having familiarized yourself with them, you will be able to understand that a foundation pit is needed to fill the stabilizing pillow and position the structure below ground level. Usually the strength of the soil is not enough. Sometimes the groundwater is too high on 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 in the best way. 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 Fence Technology
In order to avoid serious consequences, the foundation pit fence is often used. For this, the installation of tongues is used. This localizes subsidence of the soil and eliminates 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 consists in installing piles that are made of different materials. They are next to each other. The foundation pit may be secured using supports in the form of temporary fences. This applies to wooden piles, which eventually lose their integrity, so they are rarely used. Increasingly, builders give preference to metal dowels, which can be used repeatedly.