The foundation acts as one of the main parts of any building, so the life of the building will depend on the quality of its construction. At the first stage of the construction of the foundation, it is necessary to dig a foundation pit. Its shape depends on the type of foundation.
Varieties of pits
Before you start building a pit, you need to consider its main varieties. To date, there are known criteria by which pits are classified into separate subspecies. You should read them:
- need for corner fixings;
- number of slopes or lack thereof;
- presence of inclined walls of a trench or excavation.
The last factor is determined by the base, which can be slab or tape. If it is planned to build a strip foundation on the site, then the pit will look like a trench located around the perimeter and in those places where there will be load-bearing walls.
If you are planning to buildslab foundation with a basement, then the pit should be located around the perimeter of the house and in the place where the basement will be located. Before starting work, it is necessary to carry out earthworks, they provide for:
- determining soil type;
- conducting a building analysis;
- calculating the depth of the pit;
- analysis of the climatic state of the region.
The type of soil is determined by special expertise. This stage is mandatory, because it can be used to determine the depth of the foundation, which will ensure the reliability and strength of the building during operation. You can also carry out an analysis of the building that will be built on the site. It is necessary to know the weight of the building, as well as the load on the foundation. It is important to provide for the presence of the smallest details, down to the materials for finishing floors, walls and roofs.
Excavation
Before the construction of the pit, it is being developed. If you plan to do the work yourself, then it will take a lot of time, patience and effort. But it will save you money. Work should begin with determining the depth of the pit. In order to find out what the volume of the pit will be, you must use the formula v \u003d n / 6 (2a + a1) in + (2a1 + a) in1. The height of the pit is determined by the letter n, while the dimensions of the sides are a and b. The length of the pit along the upper part is a1 and b1. But the slope coefficient is indicated by the letter m.
As soon as it is possible to determine the volume of the pit, it is necessary to calculate the volumebackfill. To do this, the total volume is subtracted from the volume of the pit. Depth can be determined from the ground, not from a rough mark. Before excavating the soil, it is necessary to determine the depth at which the digging will be carried out. This value is determined by the composition of the soil and the load from the house itself. To determine the pressure of the building on the foundation, the formula a=f / a (mn / mm) should be used. In this case, the load from the building will be divided by the area of the lower part of the base. Once the dimensions of the pit have been determined, you can start digging it.
Digging process
The construction of the pit is carried out according to a certain algorithm. At the first stage, the site is prepared, the top layer is removed from it, while it is necessary to go deeper by about 40 cm. If there is additional moisture, then it should be removed from the site.
Special supports in the form of beams will prevent the soil from sliding along the walls of the pit when the soil is removed to a given depth. This is true for 125 cm. If this value increases to 500 cm, then steps are arranged in the pit, and their depth is determined by specialists.
Detailed consideration of earthwork technology
Ducting a pit is a rather complicated process. For its implementation, one person is not enough. Works in the depths of the earth are distinguished by high complexity, because it is necessary to take measures to prevent slipping of the soil. At the first stage, the fertile soil layer is removed, becauseit is highly biologically active and cannot act as a carrier base. From time to time, it changes in volume, so it cannot serve as a reliable foundation for the foundation of a building.
To remove this layer, it is recommended to use a special technique or conventional tools. The choice of the final option will depend on material possibilities. The construction of a foundation pit will provide for the need to excavate the entire area of \u200b\u200bthe house if the building has a basement. Special equipment is used without fail.
Excavation is carried out gradually, and construction equipment is installed 80 cm from the beginning of the foundation. The soil should be located near the equipment. If the construction of the foundation pit does not provide for a basement, then a strip base will suffice. Such works are cheaper than those that involve the arrangement of a slab foundation.
Dig features
Digging the pit is done with extreme care. If the soil consists of gravel and sand, then the minimum bookmark should be 100 cm. You will have to go deeper by 125 cm if you work with sandy loamy soil. Clay and loam suggest a deepening of 150 cm. Dense soil provides for a deeper foundation, which is laid 2 m.
In order to prevent soil shedding, it is necessary to provide a slope on the walls. If the height of the foundation walls is approximately 150 cm, thenthe following values must be applied. When work is carried out on sandy soil, the slope should be 60 °. With a soil slope of 45 °, the ratio will be equal to one to one. Sometimes the development and construction of a pit involves working on soil with a large amount of sandy loam. In this case, the slope reaches 75 °, and the ratio will be 1 to 1/4. When working with clay soil or one that has high hardness, the ratio will be 1 to 0 with a slope of 90 °.
Before pouring, wooden supports must be used to prevent soil slippage. Building them yourself is very easy. It is important to foresee the process of backfilling the sinuses. It is important, as it is carried out at a minimum soil pressure. Backfilling is carried out gradually, while the material is well compacted. The optimal thickness of each layer during backfilling is 20 cm. Soil compaction should be done manually.
The blind area should be made from the beginning of the seal. It is important to take care of the waterproofing of the pit, which is done even before the installation of the formwork. For this, roofing material or asbestos cement material is usually used.
Recommendations for digging
Digging technology can provide for the deepening of the base by 3 m or more. At the same time, a special steel fence is equipped, its diameter should be 30 cm. When the depth reaches 6 m, a special underground wall is required, its thickness should be 60 cm. When the depthexceeds 7 m, the thickness of the wall must be up to 1 m.
The arrangement of the bottom of the pit involves its compaction if the soil is soft enough. To do this, a pillow of pebbles or rubble is poured. At the same time, the walls will acquire additional resistance. When the soil is very wet, workers must ensure that there is drainage in the form of a layer of crushed stone. It is also necessary to pay attention to the reliability of oblique corners and parts. A support is installed from the initial part of the base of the pit. The struts should be securely braced.
In order to prevent slippage and secure the struts, you need to use a strapping bar or staples. The construction of trenches and pits, which will be deepened by more than 5 m, involves work to protect the walls from shedding. For this, brackets are installed, and a strapping beam is used to fasten the structure, which is fixed on the walls with the help of linings and bolts. This also eliminates soil shrinkage.
Anchor puffs allow you to fix the foundation pit, which is arranged during the construction of the foundation of a building with a basement. Anchors should be located at double the height of the slopes. The steepness of the slope is determined by the depth of the foundation and the type of soil. For example, if during the construction of a building on bulk-type soil, a pit is built 150 cm deep, then the lower section of the slope should be one meter from the walls of the pit.
The degree of steepness will depend on the depth of the base and the type of soil. The most appropriate value of this indicator is equal to the limit from 25 to 60°. Fromincreasing the slope arrangement angle depends on the amount of excavation work. The higher the slope angle, the more funds will be required for earthworks. The construction of pits is best done in summer or autumn. In this case, the level of soil moisture will be minimal.
Digging a ditch in winter has a higher cost, as well as building a foundation. In spring or late autumn, the groundwater level is at its highest, so these periods are not suitable for digging.
Typical flow chart for work on the excavation
TTK for excavation is compiled at the time of building design. If work is carried out in wet soils of the second group, then the depth of occurrence can be equal to the limit from 2.5 to 9.1 m. It is better to carry out work in the summer. When drawing up a layout drawing, it is necessary to mark the bottom of the pit. The drawing data is transferred to the cover, which includes pillars firmly buried in the ground. Boards are nailed to them, installed on the edge from the outside.
When laying out a foundation pit for large foundations, a contour is determined on the ground and a cast-off is installed at the corners. A wire is stretched between opposite cast-offs. The cast-offs indicate the depth of the pit. Before digging a trench or pit with slopes, poles are installed from the axis and along the edges.
If using a shovel excavator, as the density of the soil increases, the productivity will decrease. It also depends onsoil development method. This indicator is also affected by the capacity of the bucket. The performance of the excavator is increased if the boom angle is reduced.
The excavator should be located at the workplace, which is called the face. Its shape and geometric dimensions will depend on the equipment and parameters, as well as the modes of transport and the dimensions of the excavation. The arrangement of pits in soils that have high humidity provides for the location of vehicles and the excavator in such a way that the average angle of rotation of the equipment from the place where the bucket is filled to the place of unloading is minimal. This requirement is due to the fact that approximately 70% of the working time of the cycle is spent on turning the boom.
Features of fixing pits
The construction and fixing of pits is mandatory if the depth of the base for coarse soil is more than 1 m. For high density soils, this parameter is 2 m. If the above depth is not exceeded, but work is carried out in moisture-saturated soil with high the level of groundwater, then the strengthening of the pit in the slope area is carried out without fail.
Today, two methods of slope strengthening are known, the first involves the creation of enclosing sheet pile structures, while the second is a separate strengthening with grouting of the walls. For fastening, not only tongues are used, but also pipes. The most reliable method is slope grouting, but this method has one important drawback, which is expressed in high cost.
Methodused in cases where neighboring buildings are too close to eliminate vibration effects. For this purpose, you can also use sheet piling drilling. This method minimizes vibration when the supports are submerged. To strengthen slopes, in some cases, the use of sheet piles is more practical than grouting. This is because sheet piles can be removed and reused after completion of work.
Features of the foundation device
The construction of the pit (SNiP 3.02.01-87 governs this process) upon completion of this stage provides for laying the foundation. If we are talking about a tape structure, then a pillow is laid at the bottom of the pit, which will ensure the reliability, durability and strength of the building. It is a battle of bricks, crushed stone or sand. You can also use a gravel pad. Its thickness is 200mm or more.
When it comes to sand, cold water is used to compact it. Crushed stone or brick battle is laid on top. The top layer of the pillow should be as even as possible; to check this characteristic, you need to use a level. When laying the pillow, you must provide waterproofing, so that when the concrete hardens, moisture is retained for as long as possible.
The foundation in the pit at the next stage involves the installation of formwork and pouring concrete. However, first you need to carry out reinforcement. The formwork is made of boards or a metal profile. You can use any improvised means,the main thing is that the surface from the inside is even, because this will affect the appearance of the concrete structure.
At this stage, openings are provided, for example, for plumbing, ventilation and sewage. To do this, pipes of the appropriate diameter are installed in the indicated places before pouring. Pouring concrete acts as the final stage. For this, a solution of cement, gravel and sand is prepared. Recommended proportions: 1: 3: 3.
Conclusion
With independent development and installation of trenches, it is necessary to carry out a lot of work, including preparatory work. They provide for obtaining a building permit, as well as conducting geodetic studies. If you plan to do the work on the construction of the pit yourself, then this will save additional money.
