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 base, it is necessary to dig a pit. Its shape depends on the type of foundation.
Varieties of pits
Before tackling the device of the pit, it is necessary to consider its main varieties. To date, the criteria are known by which pits are classified into separate subspecies. You should familiarize yourself with them:
- the need for corner mounts;
- the number of slopes or their absence;
- the presence of inclined walls of the trench or pit.
The last factor is determined by the base, which can be slab or tape. If a strip foundation is planned to be erected on the site, the foundation pit will look like a trench located along the perimeter and in those places where there will be load-bearing walls.
If you plan to build a slab foundation with a basement, then the foundation 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 earthwork, they include:
- determination of soil type;
- 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 with it you can determine the depth of the base, which will ensure the reliability and strength of the building during operation. You can also analyze the building that will be built on the site. You need to know the weight of the building, as well as the load on the foundation. It is important to consider the availability of the smallest details, right down to the materials for finishing floors, walls and roofs.
Excavation development
Before the construction of the pit, its development is carried out. If you plan to do the work yourself, then it will take a lot of time, patience and strength. But this will save. Work should begin with determining the depth of the pit. In order to find out what the volume of the pit will be, you need to use the formula v = n / 6 (2a + a1) to + (2a1 + a) b1. 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 in the upper part is a1 and b1. But the slope coefficient is indicated by the letter t.
As soon as it is possible to determine the volume of the pit, it is necessary to calculate the volume of backfill. For this, the total volume is subtracted from the pit volume. Depth can be determined by soil, not by rough mark. Before excavation, the depth at which digging will be carried out should be determined. 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, use the formula a = f / a (mn / m * m). In this case, the load from the building will be divided into the area of the lower part of the base. Once the dimensions of the pit have been determined, you can begin to dig it out.
Digging process
The device of the pit is carried out according to a certain algorithm. At the first stage, a plot is prepared, the top layer is removed from it, and it is necessary to deepen by about 40 cm. If there is additional moisture, then it should be removed from the plot.
Special supports in the form of bars will help to prevent soil from sliding along the walls of the pit when soil will be removed to a given depth. This is true for 125 cm. If this value increases to 500 cm, then steps are arranged in the foundation pit, and their depth is determined by specialists.
Detailed consideration of excavation technology
Pit construction is a rather complicated process. For its implementation, one person is not enough. High complexity is characterized by work in the depths of the earth, because it is necessary to take measures to prevent slipping of the soil. At the first stage, the fertile soil layer is removed, because it is characterized by high biological activity and cannot fulfill the role of the bearing base. From time to time, it changes in volume, so it can not serve as a reliable basis for the foundation of the building.
To remove this layer, it is recommended to use special equipment or ordinary tools. The choice of the final option will depend on material capabilities. The construction of the foundation pit will require the excavation of the entire area of the house if the building has a basement. Special equipment is used without fail.
Digging is carried out gradually, and construction equipment is installed at 80 cm from the beginning of the foundation. Soil should be located near equipment. If the device of the pit for the foundation does not provide for a basement, then a tape base will be enough. Such work is cheaper than those that provide for the arrangement of a slab foundation.
Digging features
Digging a pit is carried out with extreme caution. If the soil consists of gravel and sand, then the minimum laying should be equal to 100 cm. You will have to go deep by 125 cm, if you work with sandy soil. Clay and loam suggest a depression of 150 cm. Dense soil provides for a deeper foundation, which is laid at 2 m.
In order to eliminate soil shedding, it is necessary to provide a slope on the walls. If the height of the foundation walls is approximately 150 cm, then the 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 one to one. Sometimes the development and construction of the pit involve work on the soil with a large number of sandy loams. In this case, the slope reaches 75 °, and the ratio will be 1 to 1/4. When you have to work with clay soil or one that has high hardness, the ratio will be 1 to 0 with a slope of 90 °.
Before starting pouring, to prevent slipping of the ground, it is necessary to use supports made of wood. Building them yourself is very simple. It is important to provide for the sinus filling process. It is important because it is carried out with minimal soil pressure. Filling is carried out gradually, while the material is well compacted. The optimal thickness of each layer during backfill is 20 cm. Soil compaction should be carried out manually.
The blind area should be made from the beginning of compaction. It is important to take care of the presence of pit waterproofing, which is done even before the installation of the formwork begins . For this, roofing material or asbestos cement material is usually used.
Pit design recommendations
The technology of excavation of pits may include deepening the base by 3 m or more. At the same time, a special steel fence is arranged, 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 depth exceeds 7 m, the wall thickness should reach 1 m.
The device of the bottom of the pit involves its compaction, if the soil is soft enough. To do this, a pillow of pebbles or gravel is poured. The walls will acquire additional durability. When the soil is characterized by high humidity, workers should take care of the presence of drainage in the form of a layer of rubble. It is also necessary to pay attention to the reliability of sloping corners and parts. A support is installed from the initial part of the foundation pit base. It is necessary to reliably strengthen the struts.
In order to eliminate slippage and ensure the fixation of struts, you need to use a strapping beam or staples. The installation of trenches and pits, which will be buried by more than 5 m, involves work to protect the walls from shedding. For this, brackets are installed, and for fastening the structure, a strapping beam is used, mounted on the walls with the help of linings and bolts. This also eliminates soil shrinkage.
Anchor tightening allows you to fix the foundation pit, which is arranged during the construction of the basement of the building. Anchors should be in double slope height. 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 a bulk type soil a pit 150 cm deep will be arranged, then the lower 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 suitable value of this indicator is equal to the limit of 25 to 60 °. The volume of earthwork depends on the increase in the angle of arrangement of the slope. The higher the slope angle, the more funds will be required for earthwork. The arrangement of pits is best done in summer or autumn. In this case, the soil moisture level will be minimal.
A pit dug in winter has a higher cost, as does the construction of a foundation. In spring or late autumn, the groundwater level is as high as possible, so these periods are not suitable for digging.
Typical technological map for work on the pit
TTK for the excavation device is compiled at the time of designing the building. If the work is carried out in wet soils of the second group, then the depth may be equal to the limit from 2.5 to 9.1 m. The work is best done in the summer. When drawing up a alignment drawing, it is necessary to mark the bottom of the pit. The drawing data is transferred to the cover, which has poles firmly buried in the ground. They are nailed to the boards mounted on the rib from the outside.
When breaking the foundation pit for large foundations, a contour is determined on the ground and a castoff is installed at the corners. A wire is pulled between the opposite castoffs. On cast-offs the depth of the pit is indicated. Before digging a trench or foundation pit with slopes, the milestones are installed from the axis and along the edges.
If you use a single bucket excavator, then as the density of the soil increases, productivity will decrease. It also depends on the method of soil development. This indicator also affects the capacity of the bucket. Excavator productivity increases if the angle of rotation of the boom is reduced.
The excavator should be located in the workplace, which is called the face. Its shape and geometric dimensions will depend on equipment and parameters, as well as modes of transport and dimensions of the excavation. The arrangement of pits in soils that have high humidity provides for the location of vehicles and an excavator so that the average angle of rotation of the equipment from the place of filling the bucket to the place of unloading is minimal. This requirement is due to the fact that about 70% of the working time of the cycle is spent on turning the boom.
Features of mounting pits
The construction and fixing of pits is carried out without fail 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 a high level of groundwater, then the strengthening of the pit in the area of slopes is carried out without fail.
To date, two methods are known for reinforcing slopes, the first involves the creation of enclosing sheet pile structures, while the second involves a separate reinforcement with cementing walls. For fastening, not only tongues are used, but also pipes. The most reliable method is the cementation of slopes, but this method has one important drawback, which is expressed in high cost.
The method is used when neighboring buildings are too close to exclude vibration. For this purpose, you can also use drilling with the immersion of piles of sheet piling. This method minimizes vibration when submerging the supports. To strengthen the slopes in some cases, the use of a tongue and groove is more practical than cementation. This is due to the fact that sheet piles after completion of work can be removed and reused.
Features of the foundation
The device of the pit (SNiP 3.02.01-87 regulates this process) after the completion of this stage provides for laying the foundation. If we are talking about a tape design, then a pillow is laid at the bottom of the pit, which will ensure the reliability, durability and strength of the building. As it is a battle of bricks, rubble or sand. You can also use a gravel pillow. Its thickness is 200 mm or more.
When it comes to sand, cold water is used to compact it. Crushed stone or brick fight 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 a pillow, you must provide waterproofing, so that when the concrete hardens, moisture will remain as long as possible.
The foundation device in the pit at the next stage involves the installation of formwork and pouring concrete. However, to begin with, it is necessary to carry out reinforcement. Formwork is made of boards or metal profiles. You can use any means at hand, the main thing is that the surface inside is smooth, because this will affect the appearance of the concrete structure.
At this stage, holes are provided, for example, for plumbing, ventilation and sewage. For this, pipes of the corresponding diameter are installed in the indicated places before pouring. Concrete pouring 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 arrangement of trenches, it is necessary to carry out many works, including preparatory ones. They include obtaining a building permit, as well as conducting geodetic surveys. If you plan to do work on the device of the pit yourself, then this will save additional money.