Pile driven reinforced concrete foundation. The device of bored piles
In the current construction business, many different reinforced concrete products are used. These are slabs, beams and panels and so on. This article will focus on reinforced concrete pile structures, which are now very often used in the construction of foundation foundations.
What are piles?
These are proven building products that make it possible to build reliable foundations.
These products are now produced from a variety of materials: metal, asbestos, concrete, etc.
Since pile shafts are designed to withstand the loads that are placed on the foundation of the structure.
They must be extremely reliable, durable and able to cope with any negative factors.
Varieties of the assortment
The following types of support shafts are made from reinforced concrete materials:
- monolithic inside, which are immersed in the ground without drilling wells or digging ditches;
- hollow inside, which are immersed in a pre-drilled well;
- stuffed, poured into the formwork with a drilled hole.
Technical characteristics of reinforced concrete piles
![](https://i2.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta2.jpg)
Most of the parameters of pile shafts are determined by the brand of concrete used in their manufacture.
For example, the brand of concrete characterizes the strength of the trunk. Concrete brand numbers show ultimate compressive strength.
In the production of reinforced concrete piles, concrete B7.5 and higher is used. The lowest compressive strength is determined by this grade of concrete.
The indicators of frost resistance and wet strength of piles are determined by the same method. They appear on the marking plate after the letters "F" and "W". For example, for concrete grade B7.5, these parameters are equal to more than 50 cyclic freeze / thaw (F50) and a pressure limit of 2 MPa of water (W2).
The mass of reinforced concrete shafts is determined primarily by their volumes. And the more they are, the more weight indicators.
The positive qualities of reinforced concrete piles of any type include:
- service life (If the foundation was erected without violating the technology, the piles will last more than 100 years without repair);
- high strength (reinforced concrete piles withstand the weight of even multi-storey panel buildings);
- stability (the trunk is driven in to a depth, which allows it to rest on the ground of a large bearing capacity);
- the possibility of using supports for construction on difficult terrain (The pile part of the foundation can be constructed from supports of different lengths.)
The disadvantages of piles can only be attributed to the severity of the products. This indicator often makes delivery and installation inaccessible.
![](https://i0.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta3.jpg)
The foundation on reinforced concrete piles is made in the area where the soil is problematic, and the building needs to be built. In areas with such soil, only reinforced concrete piles will ensure the stability of the building, transferring the load to stable layers.
The reinforced concrete pile foundation for a block building has many advantages over other types of foundations.
If we compare the construction of a columnar foundation with others, then the device of such a foundation for a house made of blocks is much more technologically advanced.
The pile foundation involves drilling wells of a given size, installing reinforcing bars in them, and pouring them with concrete.
A big advantage of this method is the ability to perform wells with a hand drill.
How to make piles for the foundation
![](https://i2.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta4.jpg)
The foundation of reinforced concrete piles is easy to do by yourself. It is only important to withstand the basic calculations:
- trunk sizes;
- gaps between trunks;
- reinforcement parameters;
- brand of concrete;
- laying frequency.
concrete mix
![](https://i1.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta5.jpg)
The pile foundation is often installed in an aggressive environment. For this reason, they need concrete that is durable, resistant to "chemistry". This property of concrete affects the durability of the pile.
On the brand of concrete, you need to consult with specialists who, after studying the soil, will recommend appropriate additives to increase stability.
Possible composition of concrete:
- cement grade 7001 hours;
- sand 1.5 hours;
- crushed stone 2.5 hours;
- water 0.5 h.
It is better for a pile foundation to order industrial concrete. If it is impossible to buy or deliver concrete to a construction site, they prepare it themselves.
Preparing the site for the foundation
Before starting the installation of piles, a site is being prepared:
- remove the roots of trees, the top layer of soil;
- mark the location of the foundation with the help of cords;
- determine the levels of the trunks above the surface;
- mark the axes of the piles.
Concreting and reinforcement of piles
After preparing the holes for the piles, "pipes" are rolled from the roofing material, which should correspond to the wells in coverage, and the length is 20-30 cm more than their depth.
At the top, the “pipe” must be made stronger, from 2-3 layers of roofing material, and pulled together with a strong wire. This end will be the top formwork. Then the "pipe" is carefully driven into the well.
If there is some water at the bottom, it's okay. But when the water fills a quarter of the well, it must be pumped out.
If such a “pipe” is not made, negative consequences cannot be avoided.
formwork
![](https://i0.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta8.jpg)
The setting of concrete occurs on the first day after the preparation of the mixture. And in order for the strength to be maximum, it is extremely important to preserve the "cement milk" in the concrete mass. It should not drain into the ground, because then the specified strength of concrete cannot be reached.
In the case of freezing of the soil surface, heaving forces will act on the rough surface of the pile more strongly if it was formed without a “pipe”.
When the wells are prepared, a reinforcement frame will be needed. For this purpose, you can take 3 bars of six-millimeter diameter reinforcement for each pile shaft. They are fastened with transverse crossbars with an interval of 50-60 cm.
Vertical rods are brought out above the piles below the height of the grillage by 2-3 cm.
After the formation of the frame in the well, the supply of concrete in 4-cm layers begins, and their compaction with the help of vibrators.
grillage device
![](https://i0.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta9.jpg)
For a grillage device for a light house, it is recommended to observe the following parameters:
- height - from 30 cm;
- the width is equal to the width of the base, and if it is not, the width is equal to the thickness of the walls of the 1st floor, but not less than 40 cm.
Dissection of the grillage with pipes is unacceptable. The deviation of the pile from the vertical is determined by a plumb line. It should not be more than 5 cm.
During the assembly of the grillage, it is necessary to carefully fix the elements on the pile heads. If the grillage beam is replaced with load-bearing reinforced concrete lintels, they are fixed to each other by welding with reinforcing bars.
After assembling the grillage, all seams and joints are filled with cement mortar or concrete.
Restrictions in the use of pile foundation
![](https://i1.wp.com/fundamentclub.ru/wp-content/uploads/2016/03/jb-cvai-dlia-fundamenta10.jpg)
This type of foundation also has disadvantages, or rather limitations that prevent their use.
Reinforced concrete foundations should not be used in horizontally unstable soils, because the building will not be resistant to overturning.
When building such a foundation, problems arise with the base.
You have to fill the space between the piles, as in a columnar base.
This requires additional funds.
The video demonstrates the driving of reinforced concrete piles IZH-3-38-C1 (C2) C-08 without formwork
The device of the pile foundation makes it possible to build buildings on problematic soils characterized by low strength, weakness, heaving, and a large freezing depth. Piles ensure the reliability of the structure. They transfer loads to stronger soil layers, which are located below the problem areas.
Pile construction
Piles are long rods that are immersed in the ground in finished form or are made in the ground itself. They have a pointed end. It is hammered into the ground with the help of special equipment. According to the method of immersion in the ground, pile structures are of various types:
- Driven piles. Their immersion in the ground is carried out using vibrators.
- Concrete and reinforced concrete stuffed piles. They are created by drilling wells and then pouring concrete.
- Drilling reinforced concrete piles. They are created by installing concrete elements in a drilled well.
- Screw - installed by twisting into the ground. Their design is in the form of a drill.
The design of piles differs in the way they act on the ground. So, the following types are distinguished:
- hanging piles, in which the load is transferred by friction of the soil on the surface of the piles;
- pile-racks, the principle of transferring the load in them occurs on solid ground, which is located under a layer of weak soil.
The design of piles is determined by the principles of placement in the ground. So, piles can be:
- single, which act as separate racks;
- combined into large pile tapes, which are located around the perimeter and distribute the load evenly;
- combined into pile bushes, which are located under the columns of the supporting frame frames of structures.
The following materials are used for their manufacture:
- Reinforced concrete. Reinforced concrete piles can be made on site if the appropriate machinery is available. For the implementation of such piles, concrete grade M200 is used. The service life of these piles is more than 100 years.
- Steel. Such piles have many disadvantages. They must be installed with a crane. The metal must be carefully treated with an anti-corrosion coating. The production of such piles takes a lot of metal.
- Wood. Piles made of wood are even pillars up to 8 m long and up to 30 cm in diameter. For piles, species of hard coniferous trees are used - pine, fir, spruce, larch. Wooden piles are cheaper than steel or reinforced concrete, but they are rarely used due to the fact that wood is prone to destruction. When using preparations for treating wood from destruction, this method is also used.
For suburban private housing construction, reinforced concrete piles with a solid section, steel screw and concrete stuffed piles are the best option. The most acceptable option for deepening is the bored method.
Back to index
Pile foundation design
What is the foundation structure? The pile foundation consists of shells or piles and a beam or slab that unites them from above, called a grillage. The grillage takes the load from the structure located above it and distributes it among all the piles.
Back to index
Pile foundations types
There are a large number of different designs of pile foundations. There are types of pile foundations with high or low grillage.
In a high grillage, the sole rises above the ground, and a low grillage is buried in the ground.
The design of a foundation with a high grillage has significant advantages over a deep foundation with a low grillage.
Advantages of foundations with a high grillage:
- With the same rigidity and bearing capacity, their construction takes less labor and materials.
- It is not necessary to carry out excavation work on the construction of a pit in the ground.
- Cheaper lintels of different designs can be used instead of sheet piling of pits.
- Precast concrete slabs can be used instead of cast-in-situ slabs that are concreted in place.
- Shells and pillars are used more efficiently.
- The erosion of the bottom of the channel is reduced.
According to the type of load-bearing elements, pile foundations are divided into foundations made of piles, shells and pillars. You can create slanted foundations. At the same time, in terms of their bearing capacity and rigidity, they will be equivalent to foundations with a slab buried in the ground.
- They can be arranged on weak soils with low strength, large freezing depth, heaving and compressibility.
- Piles transfer loads to deeper solid layers of soil and thus provide the structure with strength and durability.
- Many pile foundation designs can be installed with reduced earthwork and concrete work compared to other types of foundations.
- They cannot be installed in horizontally moving soils, namely in subsidence and swelling soils due to their insufficient resistance to overturning. In such conditions, it is necessary to install a reinforced concrete grillage.
- In the manufacture of pile foundations, difficulties arise with. In this case, it is necessary to fill all the space between the existing piles.
- A large number of mechanisms and labor costs are required. Relatively high construction cost.
Back to index
Pile foundation construction technology
The technology of building a pile foundation involves drilling wells, installing reinforcement and pouring concrete into the well.
Back to index
Foundation device
Materials and tools:
- reinforced concrete piles;
- reinforced concrete beams for grillage;
- reinforcing bars with a diameter of 6 mm;
- roofing felt pipes;
- steel wire;
- cement, sand;
- yamobur;
- manual drill;
- vibrator;
- construction plumb;
- level, water level.
Back to index
well drilling
First, a well is drilled with a manual construction drill. determined depending on the weight of the future building. The design of piles is determined depending on the loads from partitions, roofs, floors and operational loads. The maximum diameter of the used hand drill is 300 mm.
Builders drill with minimal effort due to the improved positioning of the drill blades. The length of the drill rod can be adjusted. This allows you to perform wells up to 5 m deep. You can use a drill that has a device for widening the lower section of the well.
This creates a support heel for piles. This reduces the number of piles and saves concrete. If it is necessary to make wells of a larger diameter, then quite a lot of effort must be applied. To drill such wells, motorized, electric drills are used.
For example, an electric hole drill is used to drill wells for power transmission line supports. In this case, wells up to 4 m deep and up to 1 m in diameter can be drilled. Drilling machines based on a wheeled tractor and trucks are also used.
Back to index
Reinforcement and concreting of piles
It is necessary to perform reinforcement and pour concrete piles.
After the wells are completed, it is necessary to make pipes from roofing material corresponding to the diameter of the well. Their length should exceed the depth of the well by 200 mm.
Then the upper part of the pipe is made of two layers of roofing material and pulled together with steel wire. This is how formwork is done.
After that, the pipe is installed in the well. Moreover, if there is water at the bottom of the well, it must be pumped out before pouring concrete.
Proceed to the implementation of the reinforcing cage. To do this, take three vertical reinforcing bars with a diameter of 6 mm and fasten them to each other with crossbars every 500 mm.
Vertical rods for connecting the pillars with the grillage must be brought above the piles poured with concrete to a height that corresponds to the height of the grillage minus 3 cm.
In heaving soils, the foundation grillage should be on piles at a height of 200 mm from the top of the soil. To do this, the piles are made protruding from the ground.
In moisture-saturated soils, heaving can reach 15 cm.
Then you need to fill the piles with concrete.
After mounting the well frame, concrete is laid in layers of 60 cm. Each layer is compacted with a vibrator.
A pile foundation is nothing more than a complex of piles connected into a single structure that transfers the load from the building to the foundation. Due to their design, pile foundations are widely used for the construction of a wide variety of houses and buildings.
To perform specific construction tasks for the installation of pile foundations, piles of various types are selected. In this article, we will consider what types of piles are, the material of their manufacture and methods of immersion in at a construction site.
Methods for arranging a pile foundation
Houses on wooden stilts
A pile is a vertical or inclined structure , immersed in the ground or made directly in the ground. The function of piles is to transfer loads from a house or building to the foundation (soil).
When designing and installing a pile foundation, the choice of the type of piles is carried out according to the following parameters:
- method of deepening into the ground (mounting method);
- method of interaction with the soil;
- pile device and cross-sectional shape;
- material type.
There are the following types of piles:
Depending on the method of deepening into the ground:
![](https://i2.wp.com/podomostroim.ru/wp-content/uploads/2013/11/%D0%97%D0%B0%D0%B1%D0%B8%D0%B2%D0%BA%D0%B0-%D1%81%D0%B2%D0%B0%D0%B8.jpg)
Depending on the interaction with the soil:
- pile-racks - all types of piles based on rocky soils, and driven piles, in addition, on low-compressibility soils;
- hanging (friction piles) - all types of piles that rely on compressible soils. They transfer the load to the foundation soils by the lower end and side surface.
The device of various types of piles
Driven reinforced concrete piles (in cross section up to 0.8 m inclusive) and shell piles (with a diameter of 1 m or more) can be arranged as follows:
- method - with non-stressed longitudinal reinforcement with transverse reinforcement; prestressed with rod or wire longitudinal reinforcement with and without transverse reinforcement;
- cross-sectional shape - square, rectangular, tee and I-beam, square with a round cavity, hollow round section;
- the shape of the longitudinal section is a prism, a cylinder, with inclined side faces (pyramid, trapezoid);
- design features - solid or composite of separate sections;
- lower end design - pointed or flat lower end; volumetric broadening at the end (club-shaped piles); hollow piles with an open or closed bottom end or with a camouflage heel.
Concrete piles
The device of stuffed piles:
- stuffed piles - arrange by immersing inventory pipes, the lower end of which is closed by a shoe left in the ground or a concrete plug. Pipes are immersed by driving, screwing or pressing. As the wells are filled with concrete, these pipes are removed;
- vibro-stamped piles - are arranged in punched wells. The wells are filled with a hard concrete mixture. The mixture is compacted with a vibrating stamp (this is a pipe with a pointed lower end, on which a vibratory driver is fixed);
- stuffed in a stamped bed - for this, pyramidal or conical wells are arranged in the ground by stamping, which are subsequently filled with a concrete mixture.
Drill piles:
- bored solid sections - for their device, wells are drilled in the ground (both with broadening and without them), if the soil is clayey, then the wells are drilled above the groundwater level, and the walls of the well are not fixed. In other soils, wells are drilled below the groundwater level, and the walls of the wells are fixed with clay or inventory casing pipes, which are subsequently removed. Next, the wells are concreted;
- barrettes - bored piles. They are made using a grab or soil cutter;
- bored with a camouflage heel - for their device, wells are drilled with the subsequent formation of a broadening by an explosion (for example, electrochemical). The resulting wells are filled with concrete mix;
- borehole injection with a diameter of 0.15-0.35 m - are arranged in drilled wells, into which a fine-grained concrete mixture is injected (injected). And also arranged by a hollow screw;
- borehole injection with a diameter of 0.15-0.35 m with compaction of the surrounding soil - for this, the wells are treated with a series of discharges of high voltage current pulses;
- pile-pillars - wells are drilled for their device (with or without widening). A monolithic cement-sand mortar is placed in the wells and solid elements of a cylindrical or prismatic shape with sides or a diameter of 0.8 m or more are lowered;
- bored piles with a camouflage heel - differ from bored piles with a camouflage heel in that after the formation and filling of the camouflage widening, a reinforced concrete pile is lowered into the well.
Pile material
Metal piles
Depending on the material of manufacture, piles are distinguished:
- metal;
- wooden;
- reinforced concrete;
- concrete (stuffed)..
Metal piles
They are made from seamless steel pipes with a diameter of 25 to 100 cm (and even more). In the manufacture of steel sheet piles, I-beams, and other rolled profiles are also used. Box-section piles are made from them by welding.
Typically, the end of the pipe is provided with a conical tip. If the pipe is immersed without a tip, then the earthen cone that forms under the pile during immersion, as the pipe begins to fill with compacted soil, performs the function of the tip.
To increase the strength indicators, after immersion, hollow metal piles are filled. If after installation they will experience small loads, then you can not fill them with concrete.
Screw piles
- a kind of metal piles, made in the form of a metal rod with a helical blade at the end. Products have sufficiently high strength characteristics, so they are often used in construction. The diameter of the helical blade of the pile can reach up to 2.4 m, and the depth of immersion in the ground can be more than 20 m.
Application:
the number, diameter and length of screw piles depend on the load on them and the soil conditions at the construction site. The foundation on screw piles can be arranged on reliefs of any complexity, without spending time and money on earthworks. Also, the advantages of screw piles include the fact that during their installation there is no dynamic impact on the ground, so they can be used for the construction of extensions to existing structures. An important fact for individual construction is that a pile field, like, can be completed within one day.
Screw piles are also used for the construction of high-rise mast structures and power line supports, which are subject to significant wind effects. In addition, the tip with the blade allows the structure to withstand large pull-out loads, so that they can be used in heaving soils, while not being able to “squeeze out” the screw pile to the surface.
Screw piles are also used to reinforce emergency foundations. In this case, they are mounted around the perimeter of the emergency foundation and attached to it with brackets.
To prevent corrosion and increase the service life of metal piles, they are treated with anti-corrosion agents before installation.
Wooden piles
Wooden piles
They are made from spruce, pine, cedar, larch, fir, oak. For the manufacture of wooden piles, logs with a diameter of 22-34 cm and a length of 6.5 and 8.5 m are taken, while maintaining the natural run of the logs (reducing the diameter of the trunk from the butt to the top). The bark is removed from the prepared logs, and then they are trimmed in the right places.
Depending on the design of the pile foundation, wooden piles can be either solid, i.e. made from one log, and spliced in length. Accordingly, the length of the whole product can vary from 4.5 to 16 meters, and the length of the spliced product can vary from 20 to 25 meters. For splicing, the logs are connected end-to-end with the help of overlays. If necessary, logs are spliced not only in length, but also in thickness. Wooden piles obtained in this way are called package piles.
The length of the pointed part of the wooden pile is 1.5-2 of their diameter. If there are obstacles in the ground, the pointed part is protected with a shoe. The upper part of the wooden pile is protected by a yoke or a cap.
The device of wooden piles in the ground is carried out by driving, indentation or vibration.
Application:
The price of wooden piles is usually lower than the price of metal or reinforced concrete counterparts, but at the same time, wooden products can withstand a lower load. Therefore, wooden piles are not used in high-rise construction, but they are used in low-rise construction in the construction of houses and cottages. They are also used for the construction of temporary structures, small bridges, etc.
Reinforced concrete piles
They are monolithic or prefabricated.
Reinforced concrete piles
Monolithic reinforced concrete piles often have a rectangular or square section ranging in size from 20 × 20 to 40 × 40 cm. Square piles with a cylindrical cavity are also produced with a section size of 25 × 25 and 30 × 30 cm and a wall thickness at the narrowest point of at least 4 cm.
Longitudinal reinforcement of monolithic products is carried out with steel rod reinforcement (prestressed or non-prestressed). In the transverse direction, the products are reinforced with low-carbon wire or wire rod with a thickness of 5 mm or more.
During installation, the head part of the pile perceives the shock load, therefore it is reinforced with three reinforcing meshes located horizontally in increments of 5 cm.
Prefabricated reinforced concrete tubular piles are made from separate sections that can be assembled in advance, after which installation (driving) can be carried out.
Installation of reinforced concrete piles is carried out using pile drivers, mobile cranes with pile hammers, etc. Vibration immersion is also used. It is less labor intensive and costly.
Advantages:
- dense immersion in the soil - when driving with a hammer, the soil around the pile is compacted, and its design resistance increases significantly;
- reinforced concrete driven piles can be used on weak and moving soils, as well as in variable conditions;
- such a foundation is characterized by high strength and durability;
- pile foundation can be of any shape and size.
Disadvantages:
- when building in a built-up area, it must be borne in mind that pile driving can lead to a change in soil masses. Soil movements are especially insidious in conditions of cramped, infill development, which can adversely affect the integrity of the foundations of adjacent buildings;
- the difficulty of driving reinforced concrete products - mainly this is an increased noise level both from the operation of the equipment itself for driving them, and from hammer blows on the pile;
- reinforced concrete products are more fragile than piles made of other materials, therefore, they require appropriate storage conditions. They are laid in horizontal rows, while ensuring the same orientation of the ends. Between horizontal rows in stacks, wooden spacers are laid at the grip points or near the mounting loops. Storage of round piles is carried out using special bars that prevent rolling;
- the large size of concrete products also cause some difficulties in their transportation to the construction site.
Stuffed (concrete) piles
Reinforcing cage for bored piles
Also widely used in construction. Their distinctive feature is that they are made directly at the construction site. The main technological scheme for their manufacture: a well is made in the soil by some method and filled with concrete, and if a steel reinforcing cage is placed in them before filling the wells with concrete, then reinforced concrete stuffed piles are obtained. After the concrete mixture has hardened, the resulting pile is cut.
Ease of installation makes such a foundation very popular. Its advantages include the absence of the need to transport piles.
Of the shortcomings, the following should be noted:
- it is impossible to control the quality;
- rammed piles should not be installed in soils prone to heaving or horizontal movement due to their poor resistance to overturning.
What kind of concrete to use?
Reinforced concrete and concrete piles are made of heavy concrete. Wherein:
- for non-standardized driven reinforced concrete, as well as stuffed and drilled piles, concrete of a class not lower than B15 is used;
- for driven reinforced concrete with prestressed reinforcement - concrete not lower than B22.5;
- for reinforced concrete grillages of pile foundations - heavy concrete of the class: for monolithic - not lower than B15, for prefabricated - not lower than B20;
- for embedding reinforced concrete columns in pile grillage cups - concrete not lower than B15;
- for pile heads with prefabricated strip grillages - concrete not lower than B15;
- the class of concrete used for bridge supports and hydraulic structures for embedding prefabricated elements of pile foundations should be a step higher than the class of concrete of the connected precast elements.
Applications or how to choose piles
As can be seen from the above material, there is a wide variety of different types of piles, so it is impossible to limit ourselves to the description of any one design of the pile foundation. Below are some guidelines that will help you choose the most suitable types of piles for the construction of pile foundations at specific construction sites.
House on screw piles
When choosing, it is necessary to take into account a set of characteristics:
- house design;
- required indicators of strength and stability;
- geology and hydrogeological conditions of the land plot;
- terms and budget of construction;
- availability of necessary equipment, etc.
It is impossible to determine the exact criteria for choosing a pile foundation based on the totality of the listed parameters. Below are the factors for choosing pile foundations in relation to the values of some of these parameters.
- if the construction site is formed by weak soils (silt, silty loam, peat, clay, fluid loam), then when choosing the type of foundation, several options can be considered:
In the case of silt and fluid loam, it is possible to build a solid foundation slab under the entire house or to pre-compress the silt with a load;
In the case of peat and peaty soils - partial or complete peat removal + subsequent alluvium or backfilling and foundation on a natural base;
It must be taken into account that when the foundation slab is installed on soft soil, precipitation occurs: general - up to 50-60 cm and uneven - up to 25-35 cm. less than a year;
With a significant power of peat, peat removal also requires a lot of time, labor and material costs. Most often, a technical and economic comparison of pile and slab foundations on soft soils shows the advantage of pile foundations, which provide less precipitation (within acceptable limits) + economic benefits by reducing the volume of earthworks, as well as the consumption of concrete and reinforcement;
- in the case of site planning by backfilling, driven pile foundations are preferable to foundations on a natural foundation, even when dense soils are located close to the natural soil surface, since in this case, they are designed deep, cutting through the entire thickness of the bedding;
- on sites formed by household embankments of great thickness, which cannot be used as a bearing layer, columnar foundations are made deep. Instead, it is more expedient to use driven piles that pass through the entire embankment and are buried in dense soils that lie below the bottom of the embankment. If there are solid inclusions in the embankment that cannot be pierced, then bored piles are used;
- when building a house close to beams, ravines, etc., foundations are made of driven piles, and on dry clay soil - from bored piles;
- on subsidence and swelling soils up to 12 m thick, driven piles are used, and at a thickness of 13-30 m, bored piles with widenings are used. In this case, the entire subsidence layer must be cut through, and the lower ends of the piles must be buried in non-subsidence soil;
- on heaving soils, pile foundations have an advantage over foundations on a natural foundation, tk. leaving a gap between the base of the grillage and the ground surface, it is possible to exclude the influence of normal frost heaving forces. However, it is necessary to take into account the tangential forces of frost heaving, the value of which is the greater, the longer the piles;
- with a significant change in the roof of the carrier layer from coarse and rocky soils, it is preferable to use foundations of 2 types: in the area where the roof of the carrier layer is close to the surface (up to 2.5-3 m), a columnar foundation is laid on a natural base, and in the area, where the roof of the rocky soil drops sharply - pile;
- in permafrost areas, foundations are used on frozen piles, which are immersed in wells filled with soil mortar;
- on land plots near water bodies with a high level of groundwater, the construction of a foundation on a natural basis requires dewatering for the period of construction, and during further operation, drainage devices will be required, and pile foundations without deepening the grillage are exempt from building dewatering;
- with a high probability of landslides, it is effective to strengthen the slopes of the sites with bored piles of large diameter (from 1 m) without widening, leaving casing pipes and reinforcement. With an active landslide, shell piles with rigid reinforcement are used. After strengthening the landslide slopes, the type of foundation is chosen without taking into account the influence of landslide processes.
The video talks about the features and benefits of the foundation on screw piles:
Page 15 of 17
Bored pile construction technology includes the following processes (Fig. 2.41):
- drilling in the soil of a well, fixing its walls, development and removal of soil from the bottomhole;
- lowering the reinforcing cage into the well;
- filling the borehole with concrete, usually by the vertically displaced pipe (VPT) method.
Soil development method in the well is determined by the type of soil:
- non-cohesive soils can be developed with an airlift (see previous lectures in Fig. 2.34);
- messengers - with a one- or two-rope grab or auger drill;
- non-rocky soils - with a bucket drill;
- in rock, a core drill can be used to drive annular cuts with and without core separation.
Works on pile device in a reservoir with a water depth of up to 3 m, they lead from artificial islands, fenced with a tongue, if the depth is greater - from scaffolds or afloat. Wells are drilled through casing inventory (retrievable) steel pipes or through reinforced concrete or metal pipes, which are left in the pile structure. Pipes are immersed in various ways, including driving, vibration immersion or crushing.
Rice. 2.41 - Technological sequence of the construction of a bored pile: I - drilling a well; II - drilling widening; III - installation of a reinforcing cage; IV - filling the well with concrete mix
The walls of the well are fastened against possible soil collapse using a casing pipe, excessive water pressure (in clay and water-saturated sandy soils) or a clay solution that is fed into the well (Fig. 2.42).
Rice. 2.42 - Ways of fastening the walls of the well: a - excess water pressure; b - clay solution; in - casing pipe
Using excess water pressure in the well, it is necessary to maintain the water level 5-6 m above the groundwater level or the water level in the river. The water column creates excess pressure on the walls of the well:
R = γ in· h,
where h- the height of the water column above the level of the natural water horizon in the well;
γ in- density of water.
Clay mortar has a density of 1.05-1.3 g/cm 3 that is higher than the density of the water surrounding the well. This difference provides hydrostatic resistance to the rock pressure of the soil in the well.
The first two methods are cheap and simple, but the soil can fall out into the well: its quality is not guaranteed.
Advantage of casing pipe lies in the fact that it provides the ideal shape of the well and guarantees its quality. Casing- reusable inventory structures. They consist of sections up to 6 m long joined on threaded plugs and are subject to mandatory extraction from the ground.
Stages of construction of a bored pile under the protection of the casing are clearly shown in Fig. 2.43.
Rice. 2.43 - Stages of construction of a bored pile under the protection of the casing: a - immersion of the casing; b - development of the soil of the well; c - reinforcement and concreting of the pile
To prevent soil collapse in the upper part of the well, inventory pipe up to 5-10 m long. The branch pipe is buried in the upper layers of unstable soils, after which a well is developed under a clay solution or with excess water pressure.
The immersion of the casing pipe when drilling a well is carried out, as a rule, by crushing it while rotating in a horizontal plane (“swinging”). The angle of rotation ("swing") of the pipe, which is built up during the immersion, is about 20 °, the course of immersion (rise) of the pipe for one "swing" is about 0.5 m.
Inventory or steel casing pipes left in the ground (with a closed or open lower end) can be driven into the ground with both driving and a vibrator.
The well is filled with a concrete mixture after the suspension of the reinforcing cage no later than 16 hours after the completion of drilling operations.
If it is impossible to lay the concrete mix dry, an underwater masonry should be used using the VPT method with a cone draft of 16-20 cm.
The thickness of the protective layer in bored piles, concreted by the VPT method, should be at least 10 cm.
The VPT method does not provide high concrete strength, therefore it is necessary to resort to special technologies. For example, a vibrating concrete mix is used in a well. According to another technology, a set of concrete casting equipment is used using a vibrating stamp (Fig. 2.44). With this method, the concrete mixture is fed through a vertical concrete pipe, both from a bunker and a concrete pump.
As the concrete mixture is supplied and worked through with a vibrating stamp, the casing pipe is gradually removed from the well. The strength of pile concrete when laid with vibration increases by 1.2-1.5 times.
The drilling kit usually includes:
- crawler crane (for example, Liebherr load capacity 120 t) as a basic machine with a hydraulic system and a table attachment unit;
- oscillating mechanism - a table designed to immerse and retrieve the casing (for example, a VRM table weighing 63 tons, providing a torque of 1100 tcm and a lifting force of 725 tf);
- drilling tool, for example, a grab or for the development of hard rocks a grab with teeth and a chisel weighing 10-13 tons;
- casing pipes, consisting of separate sections with joints on conical plugs;
- receiving bunker; concrete pipes with sections of 6 m and flanged joints; jib crane (for example, RDK-400) for servicing the drilling complex; concrete pump for laying concrete mixture into the well; loader for cleaning soil from the well.
In table. 2.17 shows the technical characteristics of some models of domestic drilling equipment for use in the practice of building bridges with bored piles.
Table 2.17 - Technical characteristics of domestic drilling equipment
Drilling equipment MBU-1,2 hung on the E-1258 crane. The rotation of the telescopic rod suspended from the crane boom is provided by a console with a rotor hinged at the base of the boom (Fig. 2.45).
Equipment MBS-1.7A (MBS-1.7) also hung on a crawler crane, and rotary drilling is carried out in a similar way (Fig. 2.46). With the help of an expander that opens under the weight of the rod and closes under its own weight, the weight of the bucket and the drilled soil, widening is arranged. Drilling speed in non-rocky soils reaches 3-5 m/h.
Drilling machine MBNA-1 used in the construction of not only vertical, but also inclined wells with a diameter of up to 1.0 m.
In domestic practice, for drilling poles, attachments are usually used for crawler cranes and light drilling and crane machines. Quite satisfactory in terms of technical capabilities, they are noticeably inferior to the best foreign technology in terms of reliability.
At our construction sites in recent years it has been widely used imported drilling equipment, a characteristic feature of which is the equipment of the drilling machine with a set of drilling tools for various soils, a well widener, a jacking unit for immersing and extracting casing pipes, and a concrete pump. Firm units Kato, which are very popular with bridge builders, allow the development of soil in wells with special grabs. For wells with an inclination of up to 8:1, casing pipes with a length equal to the depth of the well are used. Known auger machines and vibrating grabs of other Japanese firms. In addition to Japanese technology, domestic firms use drilling machines of firms bauer(Fig. 2.47), Bade and others (Table 2.18).
Table 2.18 - Technical characteristics of foreign-made drilling machines
Rice. 2.47 - Examples of firm drilling equipment bauer: a - BG-14; b - BG-25; 1 - mast; 2 - hydraulic cylinder; 3 - drill rod; 4 - rotator; 5 - adapter; 6 - drilling organ
Modern drilling machines- rotary or impact action. On fig. 2.48 shows a crawler crane of the company Liebherr with impact equipment (mass of impact grab - 9.1 tons). Well diameter - 150-200 cm, drilling depth - up to 70 m. Drilling is carried out under the protection of a casing pipe, the angle of rotation (swing) of which is 25 °, and the course of immersion (lifting) is 0.4-0.5 m.
Rice. 2.48 - Crane company Liebherr with impact grab weighing 9.1 t
After drilling, a reinforcing cage is lowered (hung) into the well (see previous lectures - Fig. 2.36), and immediately (or with a minimum break in time) the well is filled with concrete mix. It is not recommended to drill neighboring wells before concreting the drilled one. The well is filled most often by the VPT method. If the vibration compaction method is not used, cast concrete mixtures of high mobility with a cone draft of 16-20 cm are used. When it is necessary to lay a rigid concrete mixture in the well, 1-2 vibrators are attached to the lower end of the concrete pipe.
The intensity of laying the concrete mixture in the well should be high. It is assigned from the condition of filling the well with at least 4 running meters. m/h in height. Breaks in concreting should not exceed 1 hour in summer and 0.5 hours in winter. Use cement grade not lower than 400, cement consumption per 1 m2 must be at least 400 kg. The main condition for successful work is that the concrete pipe must always be buried in the concrete mixture by at least 1 m.
Construction of bridge piers and flyovers with foundations on bored piles-pillars produced in a certain sequence using a set of construction machines (Figure 2.49).
Rice. 2.49 - Stages of construction of a support on bored pillars:
I - crushing the casing and excavation of soil from its internal cavity; II - installation of a reinforcing cage in the well; III - filling the well with concrete mix with simultaneous removal of the casing pipe; IV - excavation after the construction of bored pillars; V - installation of formwork panels and reinforcement of the support grillage; VI - concreting of the grillage, installation of formwork panels and concreting of the above-foundation part of the support;
I - drilling machine Kato-5QTHC; 2 - Crane KS45721; 3 - concrete pump; 4 - KRAZ automixer; 5 - excavator E-3223
Reinforced concrete piles are taking over the low-rise construction market. One appearance of concrete rods inspires confidence. Not the last role is played by associations with the "big brothers", which are the basis of high-rise buildings. Nevertheless, some consider such a foundation to be the most reliable, others treat it with distrust.
An unequivocal answer to the question "who is right?" we won't find. The truth is that reinforced concrete piles have their pros and cons just like any other product. Let's talk about this in more detail in this article.
What to look out for
The design of reinforced concrete piles is based on reinforced high-strength concrete. The KKZM plant installs foundations on reinforced concrete piles made of M300 grade concrete. Products comply with the requirements of GOST 19804-2012.
Supports transfer the load from the building to the ground. As a rule, they are made from concrete with an increased level of frost resistance, that is, the product can withstand strong temperature changes. This is very important for the foundation of a residential building in our climate. When choosing piles, pay attention to the frost resistance class, which must be at least f150 or f200.
Advantages of reinforced concrete piles
It is possible to compare reinforced concrete piles, perhaps, only with piles. And the first thing that concrete supports win is load bearing capacity. Depending on the size of the section and the type of soil, one piece can withstand a load of 9 to 60 tons. For example, paired with a shallow grillage 600x400 mm, you can safely build a three-story brick house. Metal piles cannot boast of such a bearing capacity.
Another advantage is the material from which they are made. Concrete practically does not break down in soil. Due to this, the service life exceeds 100 years. In addition, this kind of piles also has such advantages as resistance to pressure drops, fire resistance and moisture resistance, and during installation it is almost impossible to shift from the design axis.
It is possible to mount reinforced concrete piles in one or two days. More about this…
How to mount?
For the installation of reinforced concrete piles, a mini-piling installation is used. The tracked vehicle moves independently on off-road, mud and snow. Thanks to the adjustable feet, the unit can drive piles even on small slopes. It can be operated year-round at temperatures from -25 to +40⁰.
With the help of such an installation, up to 40 reinforced concrete piles with a section of 150x150 mm can be driven in one work shift. That is, the foundation for a country house can really be installed in one day. It is possible to deliver the car to the construction site with the help of a tow truck.
A little about the cons
The disadvantages of reinforced concrete piles include the lack of economic feasibility. For example, if we compare reinforced concrete and screw piles, then the former are more expensive, have a greater bearing capacity, but are located on the pile field in the same way as the latter. During installation, it is impossible to grow them, since the standard length is 3 meters. If there are large drops on the site, then it will not be possible to use a mini-piling machine, since there will be nowhere to install it. In this regard, screw supports win. And finally, if you decide to use a pile foundation, you should take into account that, regardless of its type, equipping the basement will be problematic, and sometimes impossible.
Summarize
What can be built on driven piles? Almost the same as on screw piles: fences, garages, hangars, houses made of timber, logs, bricks, aerated concrete and foam blocks, frame-panel buildings, bathhouses, gazebos and industrial buildings. It is unlikely that a pier or mooring will be installed. As for the low-rise construction of residential and guest houses, reinforced concrete piles with a section of 150x150 mm and 200x200 mm and a length of 3000 mm are best suited.
Advice: when choosing, consider the type of structure and soil. If you decide to build a bathhouse or flooded soil on the site, then screw piles are ideal. If the project has a brick house, then it is better to opt for reinforced concrete driven piles.
- Economic security of the Russian Federation Political economic security of the Russian Federation
- Antimonopoly policy, its goals and methods The main direction of the antimonopoly policy of the state is
- What reforms did Witte make briefly
- Okun's law and the theory of "full employment" of the population