Comparing the technological process of creating a pile foundation with the technological process of creating columnar foundation, come to the conclusion that the first one more satisfies the requirements of modern construction than the second one. The disadvantage of the second is longer preparation, which is not always permissible from the point of view of fulfilling the construction plan. A pile foundation eliminates this problem. The process begins with drilling wells of a certain diameter, installing reinforcing elements in them, and filling them with concrete. The well can be created manually or using a drill.
Wells for piles
Piles are placed around the entire perimeter of the facility under construction. Their number is determined by the total weight of the building and operational load. Depending on the loads that act from various elements of the structure (floor, walls, roofing, partitions, etc.) and the time of operation, one or another diameter of the internal piles is chosen.
When calculating the size of the hole, it is taken into account that by hand you can dig a hole with a maximum size of 3 m. The use of a drill with an adjustable length of hoses allows you to go deeper by 5 meters or more. Wells with a diameter of 6 m or more cannot be made with a hand drill, therefore it is recommended to use motor and electric drills.
The process of concreting and reinforcing piles
After the process of digging a hole and selecting the number of piles is completed, they proceed to preparing roofing felt pipes of a certain size. In this case, the following fact must be taken into account: the length of the pipes must exceed the depth of the well by 3 meters. The creation of formwork occurs using the upper parts of pipes, which are created from three layers of roofing felt, connected steel wire. The finished formwork is lowered into the well. You can often see the release of groundwater in wells, but you shouldn’t pay attention to it if its volume is not exceeded? pit volume. If the volume of water exceeds the specified value, then pump out using a pump. Only after the water has been removed is the concrete poured.
The main task of a roofing felt pipe is to protect the foundation from column destruction. If you refuse to use such pipes, a number of problems may arise:
- It is difficult for cement mortar to grip and harden if the amount of cement laitance contained in the concrete is insufficient. The roofing felt pipe prevents the diffusion of cement laitance into the ground.
- A foundation without a roofing felt pipe has uneven edges. A roofing felt pipe solves this problem by completely eliminating unevenness. When cold weather sets in and the soil begins to freeze, these irregularities will be the weak points in the concrete pile.
Let's move on to consider the reinforcement process. The frame is made from reinforcement using rods with a diameter of at least 6 mm. They are fastened with crossbars, each of which has a size of 6 m. To more effectively connect the post to the grillage, the reinforcement rod is placed just below the height of the grillage. To do this, just lower the rod a couple of centimeters.
Organization of the grillage
In the construction of pile foundations, two types of grillages are used. The first is a prefabricated one made of reinforced concrete beams, the second is monolithic.
To properly build a grillage, you must adhere to the following recommendations:
- The height should not be more than 3 m.
- The width of the grillage for single-row piles should be equal to the width of the basement room. If this is not available, they are guided by the thickness of the load-bearing walls on the first floor. However, the width should not exceed 4 m.
If the grillage is assembled from prefabricated parts, then Special attention should be addressed reliable fastening on the pile head. To realize this, when concreting the pile, an additional element is introduced into the structure - a T-shaped rod. The pile head should be covered horizontally with an additional reinforcement rod to which the limiting plates are welded. The width of the plates is selected so that it does not exceed the width of the pile. Remember that the height of the head should be sufficient to grip both the post and the mounted part of the grillage. After this, the resulting joint is concreted, and the protruding reinforcement elements are welded to the mounting loops. When the process is completed, the seams are filled with concrete or cement.
Before you start laying the walls, it is recommended to check at what level the grillage is located. If necessary, they are leveled with cement mortar so that the level corresponds to the same marks. The final step in checking the correctness of the building plan will be to measure the diagonals and all sides.
When is it prohibited to use a pile foundation?
Cases where a pile foundation does not prove its effectiveness are its disadvantages. There are only two of them, and these are:
- Pile foundations must not be used in unstable soils, as there is a risk of the structure overturning. Such soils require the use of only a strong reinforced concrete grillage.
- It happens that the pile foundation interferes with the construction of the base.
- Additional costs, since cracks and spaces between piles must be filled with concrete.
Video - installation of piles for a pile foundation
The most common type of foundation for any structure is strip foundation due to its quality characteristics and reliability. But it is not always possible to arrange strip base. Sometimes situations arise when construction has already begun, but when digging a trench it is discovered that there is unstable soil at depth, in which this type of foundation simply will not be reliable. If groundwater is close and the soil itself is loose, then the foundation will not be strong and will collapse over time, which will entail the destruction of the structure itself.
When to install a pile foundation
The technology for constructing a pile foundation has been known for a long time. It was previously used in construction in flooded areas by driving piles into the ground. This process took a lot of time and effort, but it guaranteed the salvation of property when built on problematic soil.
Pile foundation and this moment is a salvation when building on weak or overflowing soils that are not suitable for the construction of another foundation.
A pile-type foundation is much simpler to implement than, for example, a columnar foundation, because there is no need to dig holes, arrange formwork and fill in cavities. According to the technology, piles are screwed into the ground using special equipment, and holes for them can even be made with a hand drill. The installation of pile foundations is widely used in the construction of cottages and country houses, as well as dachas and industrial facilities.
The main reason why a pile-type foundation is installed is the weak soil at the construction site. Such soils include those that have a plant type with the presence of peat or humus, loess-type soils that become unstable when moisture enters them, sandy-clayey soils that are highly saturated with water, clay soils and saturated loams.
Since the upper surface of the soil is not stable, there is a need to transfer the weight of the building to denser soil, which is deeper and support can only be achieved with the help of piles.
Also, in order to reduce the amount of work during construction on too strong soil, piles can also be used. With their help, the volume of excavation work will be reduced and there will be no need to spend money on digging a pit, removing soil from the construction site and further concreting the foundation.
For example, in order to install a foundation pile, the length of which is 3 meters and a diameter of 30 cm, you will need to dig only 0.2 cubic meters of soil, whereas when installing a strip foundation you will need a whole trench.
Classification of pile foundation structures
At the moment, pile foundations are divided into many different types, which are distinguished by the type of piles and the technology of their manufacture, as well as by the process and level to which the piles are immersed in the ground and the structure of the grillage itself and have their pros and cons. We will pay special attention to those types that can be done independently.
There are screw piles, which are represented by a design that resembles a long and impressively sized screw, which is driven or twisted into the ground due to the presence of a spiral surface at the bottom. There are also bored pillars, which are created by digging holes, reinforcing them and pouring concrete.
There are also drilling piles that are suitable for installation only in ready-drilled wells.
Depending on the method of influence, piles can be divided into structures:
- Hanging type - the load is transferred by friction of the soil against the walls of the piles.
- Racks with the help of which the load of the building is transferred to solid ground, which is located at a sufficient depth.
Also, piles can be divided depending on the type of location. They can be:
- Single type, that is, free-standing supports
- Pile tape element for more correct load distribution
- Pile bushes, which are located where the load is greatest, for example, under load-bearing walls.
What are piles made of and how are they placed?
Usually the location of the piles is strictly vertical, but if the soil is subject to frequent displacements, then inclined installation can be organized.
To make piles you can use:
For private construction, reinforced concrete piles with a solid cross-section, as well as steel screw-type piles, are best suited.
DIY pile foundation
Let's consider the algorithm for installing bored piles, since they are the most common in private construction. In short, the technology involves the initial drilling of a well, installation of ready-made reinforcement into it and pouring concrete.
Important! Drilling can be done with a hand drill.
Well preparation
In order to determine the number of piles in the foundation, you need to accurately calculate the loads that the house will produce on the foundation. This includes not only the weight of the structure itself, but also operational loads.
It is imperative that if you plan to carry out work with a hand drill, you need to take into account the fact that it can make a maximum hole diameter of 30 cm, but the length can be adjusted and reach 5 meters.
The drill is designed in such a way that a person spends a minimum of effort, and the result is high-quality. It is also possible to make such wells, the lower part of which expands, which will help save concrete and provide support for the pile.
If the load of the house is such that a larger diameter of installed piles is needed, then the best option will be the use of an electric or motorized drill.
Installation of piles
Before installing the piles itself, you need to prepare some kind of formwork. For concrete piles it is made of roofing felt. Three or four layers of it are taken and twisted into a pipe corresponding to the diameter of the drilled well. It is necessary to ensure that the resulting pipe is 20-30 cm longer than the well. The twisted roofing material is fixed with steel, not rigid wire. The prepared pipes are inserted into the wells.
Important! Formwork made of roofing felt is required to ensure that the piles are reliable and durable.
It happens that a little water forms at the bottom of the well; if there is very little of it, then this is not a problem, but if water occupies ¼ of the well, then it is necessary to pump it out before pouring concrete.
After this, you need to prepare the fittings that are connected to each other. You can take three rods and install them in the well. The height of such rods should be higher than the pile itself and slightly higher than the grillage, so that the connection can be made in the future.
After the reinforcement cage is ready, you need to pour concrete into the prepared pipe to a height of 40 - 60 cm and compact it using vibrators, without touching the reinforcement bars.
Grillage installation
A grillage is a structure that connects piles and helps the load from the building to spread evenly across them. The grillage can be monolithic, prefabricated or mixed, as well as high and low. A low grillage is placed on the surface of the ground, thereby transferring the load to the surrounding soil. The load from high grillages rests entirely on the installed piles.
Important! The grillage cannot be crossed by a pipeline or other utility service.
The height of the pile foundation grillage must be at least 30 cm, and the minimum width is 40 cm, usually equal to the width of the base of the house.
Features during construction
A foundation on piles has certain nuances that are mandatory during preparation and installation:
- It is not recommended to install a pile foundation in soil that subsides and has horizontal movements.
- Before building a house, you should definitely pay attention to whether a base will be needed. When settling in ground floor, the gaps between the piles will need to be filled, and this will take a lot of time, effort and money.
- When installing a pile, special attention must be paid to the presence of reinforcing rods protruding from it, so that the piles can be connected to the grillage together.
- After installing the grillage, be sure to check its horizontalness and, if necessary, level it using concrete mortar.
Conclusion
Installation of a pile foundation under a private house- a very serious matter. Before actual construction, it is necessary to carefully calculate everything and carry out soil surveys. This process is best left to professionals, since only they will be able to conclude whether this type of foundation is suitable for the existing soil. Before installing piles, be sure to think through all the pros and cons of the design, so that their installation does not turn out to be a huge mistake in reality. initial stage construction.
Strip foundations on piles have been used for quite a long time. Its use is especially indispensable on weak and watery soils. The presence of abundant groundwater can render a monolithic strip unusable, but not piles. They form a uniform point load along the entire perimeter of the building, and the reinforced concrete tape connecting them creates a strong fixing strap.
How to lay a strip foundation
Typically, foundations of this type are laid in inclined (from 3-5° from the horizon) soils and are able to ensure the stability of the structure even in difficult geophysical conditions.
The trench is opened under all load-bearing walls to a depth that depends on the degree of inclination of the soil surface. The piles are immersed around the perimeter at a distance of 2 meters from each other. A sand cushion with a depth of at least 20 centimeters is poured into the bottom of the trenches.
For this purpose, different ones are used, which will depend on the condition of the soil at the construction site and the time of year. If the construction of the foundation is carried out in winter, it is undesirable to carry out work at temperatures below -10 degrees.
Our company can carry out driving piles in frozen soils Byspecial technology.
In weak soils, which are often found in the Moscow region, piles can be driven by vibration, which significantly reduces the cost of piling work.
Why is it better to choose a strip foundation on piles?
A monolithic foundation is a solid structure, and seasonal changes in soil have a destructive effect on it, significantly reducing its service life. We should not forget that the soil does not rise and fall evenly. Hence, monolithic foundation, under the influence of different pressure, it may simply crack.
Piles, unlike a monolith, are not subject to ground vibrations. The soil, expanding or contracting, only slides along the walls of the piles, without carrying them out. The reserve of the ground pile area will eliminate the possibility of the building skewing in the event of an uneven ground drop.
Rice.: House with strip foundation on stilts
Foundation marking
Stages of marking:
- Preparatory stage. This stage in the construction of a foundation consists of thoroughly clearing the future construction site, namely removing debris, unnecessary boards and wooden products. If there are significant holes or uneven spots on the site, they should be leveled for further comfortable construction.
- Marking. The main point in marking is determining the correct width of the monolithic tape. It is better to outline it with a reserve. So, for example, the optimal width of the tape for a house is forty centimeters, but with a trench depth of at least sixty centimeters. For a log house, you should definitely make a reserve, that is, fifty centimeters of width and sixty centimeters of depth.
- Checkpoints. The placement of control points for piles begins with corner positions plus exactly one pile in the center of the house. Next, each side of the perimeter from the corner piles is divided equally - this is how secondary control points are set.
Rice.: Marking strip foundations on piles
Piles used
The piles used for such foundations can also be different: wooden, concrete, steel, screw, with a round or square cross-section - it all depends on the condition of the soil and the scale of the project.
Rice.: Reinforced concrete piles
Construction technology
Making formwork for the grillage
To encircle the pile field into a single whole, they often resort to technology such as installing a grillage. It means a frame, which can be made of either reinforced concrete or timber, which covers the load-bearing sides of the perimeter. A wooden grillage is used very rarely, as it is intended only for piles made of wood.
The formwork is installed in the trench in such a way that its height ensures the filling of the base, and then the reinforcement structure is installed, also along the entire perimeter of the future foundation. A moisture-proofing material is laid between the reinforcement and the formwork, and the trench is filled with M-200 concrete.
As a result, after complete hardening of the concrete, a monolithic strip of reinforced concrete on piles is obtained - a strong and stable structure that ensures the strength of your home.
Rice.: Grillage for pile foundation
The grillage installation technology is completely similar to the installation of a conventional monolithic tape. Removable formwork for grillages is usually made from wooden panels or chipboard sheets. The main condition is a strong connection of these elements, since significant pressure will be exerted on them. It is best to make supports at a distance of a meter from each other when installing the formwork. They will allow you to firmly hold the bottom of the formwork trench.
If you started digging a pit for the foundation of a future house and as you went deeper you discovered that the soil was not suitable for a strip foundation, then you will have to change tactics. Why? Because the low density of the earth or the presence of groundwater will not allow an ordinary foundation to maintain its strength and integrity of the house built on it. In this case, the optimal solution would be to manufacture a pile foundation, which will achieve the required result. There are several solutions to this problem. In this article we will look at how you can make a pile foundation with your own hands.
The technology of driving piles in places of frequent flooding is especially relevant and has found wide application in the construction of houses. Previously, logs were used as piles, which were manually driven into the ground. This made it possible to build a house raised above the ground up to two meters, which protected the structure during the next flood. Although this method is painstaking, it is effective, which is why this technology has found application in our time. It is especially relevant when the future building is built on relatively weak soil.
The pile foundation has a number of advantages that allow it to be the most popular among builders. The use of piles allows you to do without trenches or formwork; in this case, you will not have to fill up the sinuses. Moreover, the piles are driven into the ground using special equipment, which greatly facilitates the work.
For a bored pile, you can cut a hole using a hand drill. This technology, which consists of making a pile foundation without the use of machinery, will allow you to equip the foundation with your own hands.
Advantages
Often, when building a house, it is discovered that the top layer of soil is quite weak. These types of soil include:
- saturated with humus,
- peat,
- loess-like,
- with groundwater close to the surface.
If the soil on your site fits one of these descriptions, and you need to build a house, then the ideal solution to the problem would be to install a pile foundation. Also, thanks to the use of this technology, the volume of land work is significantly reduced.
For a pile three meters long and 300 mm in diameter, it is necessary to dig 0.2 m³ of earth. If a strip foundation is used, then the volume of earthworks will increase several times.
You can also add the fact that large mountains of earth left over from digging trenches for a strip foundation will need to be removed, which will lead to additional costs.
Main characteristics and types
The design of a pile foundation may differ depending on the choice of piles, as well as the method of their production. Such a foundation may differ in the depth of immersion of piles, their placement and types of developments. What are piles? They resemble a long rod that plunges directly into the ground. Mainly, the finished pile is immersed. To protect it from splitting when struck, a steel ring is mounted on the upper end. There is also a technology for making piles in the well itself. To do this, a well is drilled, which is then reinforced and concreted.
Let's take a closer look at what the differences between piles are.
And so, the process of driving piles is different. For example, screw piles, which resemble a drill, are driven using the twisting method.
There are also cast-in-place concrete or reinforced concrete piles. Their production is carried out in the soil itself in a pre-prepared well. At the end preparatory work metal frame reinforcement and concreting are performed. There is a variant of drilled reinforced concrete piles, which are immersed in a finished well. Well, driven piles, which are placed into the soil using special equipment, for example, a vibratory driver.
Piles differ in the method of impact on two types, namely racks and hanging ones. As for the last option, the load is carried out through friction of the earth against the walls of the pile. Well, the racks transfer the entire resulting load to dense soil, which is located under a layer of weak soil. The advantage of this type is that it has no sediment. The method of placing piles can also be done using different methods:
- Singles. They serve as a free-standing support.
- Combined into pile strips. Their distribution is carried out evenly along the entire perimeter of the foundation, and accordingly the load will be uniform.
- United into pile bushes. In this case, the piles are placed under the column of the supporting base of the house.
Piles can be made of wood, steel and reinforced concrete. The peculiarity of reinforced concrete piles is that they are manufactured on site using M200 concrete. The service life of such a product can exceed 100 years. As for steel piles, they have a number of disadvantages. For example, to work with them it is necessary to use special equipment, and the metal must be carefully treated with an anti-corrosion liquid. This method is the most expensive.
Coniferous trees with a diameter of up to 340 mm and a length of 8500 mm are used as wooden piles. The pillars are thoroughly cleaned. Although this method is considered one of the cheapest and simplest, it is used extremely rarely.
Directly in the ground, piles can be located exclusively vertically. However, in some cases they are driven in at an angle. This is usually done in soil with a horizontal force. For example, in an area that regularly experiences large amounts of precipitation and snow melt, which in turn causes soil movement. For suburban construction, reinforced concrete piles, cast-in-place and screw-type, are most often used.
Construction technology
To make a foundation, it is necessary to drill a well of the required diameter. Afterwards, reinforcement is placed in the finished well and everything is filled with concrete. You can make such a pile foundation with your own hands. Now let's look at the sequence of work.
How to determine the number of piles for each building? To a greater extent, this will depend on the total weight of the house, as well as possible operational loads. This includes the loads of the floor, partitions, roof, etc. When calculating, it is important to take into account the diameter of the hand drill. In a specialized store you can purchase a drill with a diameter of 300 mm. To drill a well five meters deep and deeper, the length of the rod can be adjusted independently. An important point in drilling is that the drill blades are placed so that the process is easier. You can buy a drill that will expand the bottom of the well, thereby creating a heel for the pile at the bottom. This technology allows you to significantly reduce the number of piles, and accordingly there is a big saving in preparing the concrete mixture. If there is a need to drill a 600 mm well, then it is best to use electric and motorized drills, for example, an electric pit drill.
Concreting and reinforcement of piles
After completing the drilling of the well, it is necessary to make special pipes from roofing felt, made according to the diameter of the well. Their length should be 30 cm greater than the depth of the pit itself. The upper protruding part should be tied with wire, because it will serve as formwork. Afterwards, carefully insert this pipe into the well.
In some cases, it may appear at the bottom groundwater. When there is only a little of it, there is nothing to worry about, but if it fills the hole by a quarter, then it is best to pump it out a little.
Why is the so-called “pipe” necessary? In fact, its use will prevent Negative consequences. At the point when the concrete is setting, sufficient milk in the concrete mixture will be key. If you do not use pipes made of roofing felt, then this “cement laitance” will be absorbed into the soil, and the manufactured structure will not have the necessary strength.
To further strengthen the structure, a reinforcement cage can be made. To do this, it will be enough to take three reinforcement rods Ø 6 mm and fasten them together with transverse rods, at a distance of 50 - 60 cm from each other. To connect the pillars and the grillage, the vertical rods must extend above the product being poured. Once the frame is placed in the well, it can be concreted. The fill is 50 cm, it is advisable to compact the concrete with a vibrator, as this will help prevent the appearance of voids in the pile foundation.
What is a grillage? This special design, ensuring uniform distribution of the load on the ground transmitted from the piles. It also combines several piles into one whole structure. Grillages can be of several types, for example, prefabricated monolithic, monolithic, prefabricated, low and high.
If you use a low grillage, then it is placed at the bottom in the ground, respectively, the vertical part of the load is completely transferred to the soil, and using the upper grillage, the entire load will be taken on by the piles. If the future house is relatively light, then it is important to adhere to the following parameters: the height of the pile is at least 30 cm, and if they are placed in a single row, then across the entire width of the base. In the absence of a plinth, the height must be at least 40 cm. In no case should you cross or cut the grillage for carrying out various types of pipelines. Moreover, the total deviation from the center of the pile after concreting should be no more than five centimeters.
If you are installing prefabricated elements yourself, then it is extremely important to carefully secure it to the pile head by laying a horizontal reinforcing bar on it. Its height must be sufficient to enable it to be connected to the grillage during installation. After this, without fail, the installation joint is concreted, and the vertical rod is welded to the grillage loop. After the grillage is fully installed, it is recommended to fill each joint and seam with fine-grained concrete. Before the construction of the house itself begins, namely the erection of walls, it is necessary to ensure the plane of the grillage and, if necessary, level it with cement mortar.
Restrictions on use
So, as you can see, this technology has big amount benefits. However, in some cases the use of a pile foundation is not recommended. Here are two main reasons:
- If the existing soil has horizontal movement, namely, it has the characteristic of swelling soil or subsidence soil, then the use of a pile foundation is limited. To determine this, you can use the services of a laboratory. After examining the characteristics of the land, appropriate conclusions are drawn.
- In the process of arranging a pile foundation, certain difficulties arise during the construction of the basement. Costs increase due to the complete filling of the space between the piles, similar to a columnar foundation.
So, now you understand more about how to make a pile foundation with your own hands. Despite the fact that this process is quite labor-intensive, making a pile foundation with your own hands is quite possible. Moreover, pay special attention to the nature of the soil, because having a large number of advantages, it is impossible to construct such a foundation under some conditions. When making the final decision regarding the choice of foundation, consider all its pros and cons.
If you already have experience in building a pile foundation with your own hands, we will be glad if you share your experience. Leave your comments, which will be objective. Most likely, your knowledge will be useful to many!
Video
This video shows how to make a columnar reinforced concrete foundation.
This video shows how screw piles are screwed in and the further arrangement of such a foundation.
Probably many of us have seen in the village or on summer cottages houses that do not touch the ground. They seem to be slightly raised and floating in the air, resting on something invisible and at the same time solid. This is a pile foundation, consisting of many individual rods buried in the ground. How can these relatively small elements support the weight of the house? Is it possible to build any house on such a foundation and what types of pile foundations exist today? Let's figure it out.
This type of building foundation is popular in areas where weak, floating or submerged soils predominate, and where dense, hard soils are located quite deep. Also, its undoubted advantage is considered to be high speed of construction and cost-effectiveness compared to shallow foundations, because they do not require digging a foundation pit. This is especially true for small private buildings, the weight of which allows the use of such technology.
The main element of this type of foundation is rods buried at the base of the building or directly into the ground, which are called piles. Their main purpose is to uniformly distribute the entire complex of loads on the ground. A characteristic difference is the grillage - a beam, strip foundation or slab designed to increase the design loads on a pile foundation.
Why is a grillage needed?
Since single piles can take on a small load, a grillage is installed for most pile foundations. This is a kind of plate, strip or beam that connects the piles together into a single element. This significantly increases the bearing capacity of the foundation.
Monolithic grillages in the form of a slab or tape are necessarily reinforced, and in accordance with engineering calculations that determine the permissible loads on deflection and tension. Their penetration into the ground, depending on the type of piles and the nature of the loads, can be superficial or shallow.
There are three different types of pile caps:
Materials for making foundation piles
Depending on the magnitude of these same loads and the purpose of the building, piles are made from the following materials:
The choice of material for piles is also influenced by the availability of a particular technology, the geological features of the development region, and the nature and characteristics of the building under construction. Based on all the collected research and analysis, a pile foundation project is created.
What types of piles are there?
The classification of the Soviet construction system included about 150 types of piles. Their typology is also quite extensive, and today modern technologies have been added to them. Let's look at the most popular ones.
Based on the nature of placement, pile foundations are divided into the following types:
According to the type of deepening, there are the following types of piles:
Punching method– this method involves punching holes directly into the ground. Their shape corresponds to the cross-section of the pile, and can be pyramidal or conical. Next they are filled with concrete mixture. 
The procedure for calculating pile foundations
After a geological analysis of the soil at the construction site has been carried out, engineering calculations of the foundations begin. This process involves taking a foundation type as a preliminary basis, calculating it, and calculating the characteristics of an alternative foundation type. This is done in order to accurately verify the rationality of the design decision made, as well as its economic justification.
Pile foundations are calculated in accordance with the provisions of the following documents:
- SNiP 2.02.03-85 “Pile foundations”;
- SP 50-102-2003 “Design and installation pile foundations».
The design of pile foundations is drawn up on the basis of geological surveys, information about the structure and complex loads. It consists of the following points:
- Pile layout plan. It displays their connection to the axes of the foundation;
- A diagram of a geological section with a layer-by-layer indication of the location of a particular type of soil. It also displays the position of the piles, their marks and references;
- Installation plan for the grillage or rand beams, on which the position of the piles is marked;
- Formwork and reinforcement drawings of grillages, indicating the loads on them;
- Explication of piles showing their standard sizes;
- Technological specification - type of hammer, accepted load on the pile and tolerances when driving it.
At the first stage of engineering calculation, the type of pile is selected for the pile foundation, as well as its design, which includes the material, cross-sectional shape, and the length of the pile.
Based on the nature of their work or interaction with the soil, all types of piles are divided into two main groups:
The length of the pile depends on the depth of suitable soil into which it is buried. Weak soils - peat, silt, bulk, flowing - must be cut and removed to dense ones. In this case, the elevation of the grillage is also taken into account. With central compressive load, the minimum pile length is 2.5 m, with additional horizontal and moment load – 4.5 m. It is necessary to calculate the length of the pile so that its end goes into load-bearing soil at 1-2m. In soils of high density, piles are used whose lower end is open, in weak ones - closed.
The strength of the material and soil is determined by such a parameter as the bearing capacity of the pile. Its resistance is determined based on the material it is made of. For suspended piles this calculation is usually not done, since this parameter is usually higher than for soil.
The soil resistance of a pile is calculated using the following methods:
- Using tables and formulas from SNiP;
- By testing the pile with static load;
- By testing the pile with dynamic load.
There are also special cases in which the definition bearing capacity doesn't fit general rules. Separate calculation methods are provided for them, indicating calculation formulas and tabular values. This applies to piles located on peaty, silty and subsiding soils, and piles that are pulled out.
Grillages, especially monolithic ones, are calculated separately for punching on inclined planes, destruction along oblique cracks, and bending. There are two main procedures for calculating grillages: for walls and for columns.
In addition to uniformly loaded pile foundations, there are also eccentrically loaded ones. These are foundation structures whose load does not pass through the center of gravity of the area cross section piles passing through the plane of the upper ends falling on the bottom of the grillage. When calculating such loads, the number of piles in the outer rows is increased, and in this way they strive to equalize the pressure on the ground.
Step-by-step instructions for installing a pile foundation
For country houses and cottages, a type of foundation such as a pile-strip foundation is often used. We will analyze its construction in order.
- Laying out the site - involves leveling the terrain and removing excess soil to level the site for construction. During this work, wooden pegs and construction cord mark the outer perimeter of the building, as well as the dimensions of the trench for the grillage;
- Digging a trench under the tape is done using special equipment or manually. The depth and width of the trench is determined by engineering calculations, taking into account the formwork and backfilling of soil. At this stage, the presence and depth of a pit for a basement or technical structures is determined;
- Drilling wells for piles - depending on the type of piles chosen, holes are made in the ground. In some cases, it requires compaction at the very bottom, and sometimes, on the contrary, a smaller size, as is the case with driven piles. The interval is taken according to the accepted load calculation;
- Deepening of piles is done manually or using special equipment. At this stage, the presence of basements and technical rooms located below the zero floor level of the building is taken into account. If pipes are chosen as the material for the piles, their outer walls are waterproofed bitumen mastic or roofing felt, and the internal cavity is reinforced and filled with concrete mortar;
- Installation of a reinforced frame for a grillage - for better fastening, it is mated to the reinforcement coming out of the racks. The frame is securely installed in the trench using soft binding wire. It should not touch the bottom of the trench, nor extend beyond it from the outside;
- Installation of formwork for the grillage is carried out by analogy with a strip foundation, securing the formwork panels along the edges of the trench. The height of the panels should be chosen with a margin so that the soil does not get inside the formwork when concreting the tape. The walls of wooden panels are lined with polyethylene tape to extend the service life of the formwork;
- Concreting - concrete is poured at the final stage after all necessary preparations. It is best to use concrete prepared in specialized factories in strictly proportional quantities and delivered to the site by automixers. Using special sleeves or gutters, the tape is poured in one go. At the same time, concrete is compacted using vibrators;
- Dismantling the formwork, backfilling - the formwork is removed after a few days, removing the panels from the trench. The last stage of foundation work is backfilling with soil.
Use soil removed from the trench for backfilling or sand and gravel mixture, additionally tamping it. At this stage, the foundation tape is insulated. To do this, use sheets of polystyrene foam, securing it with glue.
The typology of pile foundations is extensive and diverse. Until recently, it was impossible to make them without the help of heavy special equipment, the use of which required considerable funds. In addition, the construction site itself had to be prepared for such a large event. Modern pile foundations for low-rise construction compact, economical and easy to erect structures.
It may take only a few days to set up such a system. And this despite the fact that it will support a full-fledged residential building. All that remains is to do a soil analysis, select the appropriate type of piles and grillage for them, and get to work!
The video is dedicated to modern technology pile foundations based on metal screw piles, united by a scalded grillage made of channel. The advantages of this method of constructing a foundation, its clear application in house construction, as well as the mistakes of builders and possible reasons their occurrence.