Reinforced concrete piles: specifications and installation recommendations

Reinforced concrete piles are the most demanded type of supports for organizing a pile foundation. This is due to their durability, high bearing capacity, moisture resistance and the ability to install using several technologies.

Reinforced concrete piles (RC) are a reinforcing cage that is poured with concrete mortar. The length of the finished product can be from 3 to 12 m.

Reinforced concrete piles are used when organizing a foundation using driving technology. Their use allows you to strengthen the base and reach solid soil layers.

Visually, they represent bases with a round (hollow or filled), square section. They differ in diameter and height, which determines the bearing capacity and scope of application. In addition, the strength indicators depend on the concrete grade used. The higher it is, the more reliable the elements are.

To create reinforced concrete piles, cement is used, the brand strength of which is not less than M100. Not only the compressive strength of the pile depends on the performance characteristics of concrete, but also frost resistance and moisture resistance. The last parameters for concrete grade M100 are F 50 (that is, the structure can withstand up to 50 freeze / thaw cycles) and W2 (water column pressure) - 2 MPa. The weight of the support is determined by its dimensions, and also depends on the density of the type of concrete used.

Usually, more dense concrete grades M-250, M-300, M-400 are used. The frost resistance of such products reaches 150 cycles, and the water resistance coefficient is at least 6.

Due to the increased resistance to the possibility of driving piles to great depths, their use becomes possible on moving soils (including in the zone of increased seismic activity), on clay, heaving and weak soils, in water-saturated and swampy soils.

Reinforced concrete piles can be used not only as the foundation of the foundation, but also used to prevent the pit from crumbling, strengthening the soil and the existing pile foundation. For this, reinforced concrete supports are immersed at a short distance from the existing structures, performing the function of a second pile. In addition, with additional strengthening of the foundation, the type of support under consideration can be carried out beyond the existing foundation and connected with it through beams.

Among the advantages of reinforced concrete supports, several characteristics are usually distinguished.

• Long period of operation - up to 100 years, subject to the installation technology. Feedback from the owners suggests that such a foundation can last up to 110-120 years without requiring major repairs.
• High strength indicators - on average, one support can withstand from 10 to 60 tons. Due to this feature, this type of pile is used for the construction of industrial facilities, multi-storey residential buildings, and structures made of heavy panels.
• Structural stability on all types of soil, which is achieved due to the significant deepening of the concrete pile. This, in turn, allows the concrete elements to rest on deep soil layers with maximum bearing capacity.
• The ability to carry out construction on moving, relief soils, using piles of various lengths.

Among the disadvantages is the significant mass of the structure, which complicates the process of transportation and installation of elements.

Production is regulated by TU (technical conditions), the main points of which are regulated by GOST 19804, adopted back in 1991. The service life of the products is 90 years.

Reinforced concrete products that comply with the specified GOST are used in single and multi-storey construction from various materials, in the construction of transport, engineering, bridge structures, agricultural and industrial facilities, and hydraulic structures.

GOST 19804-2012 is a normative document regulating the features of production of factory-type driven reinforced concrete piles. If we are talking about reinforcement, then the steel used must meet the requirements of GOST 6727.80 and 7348.81 (requirements for wire based on carbon and low-carbon steel used as reinforcement).

The construction of bridge structures involves its own regulations. The supports used must comply with GOST 19804-91. For their manufacture, concrete with the strength of M350 is used, the structure itself is reinforced with longitudinal reinforcement. Only such elements will ensure the strength and reliability of the entire structure of the future bridge.

The same monolithic piles are used in the construction of high-rise multi-storey buildings, large-scale industrial facilities. The sequence of selection, the method of burying, quality control and the peculiarities of testing driven piles are reflected in SNiP 2.02.03 -85.

The classification of supports of this type can be carried out based on several criteria. In general, all reinforced concrete piles are divided into 2 types - frames, poured with concrete directly at the construction site and analogues, manufactured in the factory.

The type of piles in some way depends on their device - the installation technology. So, piles, which are poured directly after installation into the ground, can be mounted by driving in with hydraulic hammers, by means of vibration deepening, or by indentation technology under the influence of static (constant) pressure.

Depending on the design features, reinforced concrete piles are divided into several types.

They represent a solid support with a rectangular or square section, although piles with a round, trapezoidal or T-section, the size of which is 20-40 mm, are possible. The bottom end is pear-shaped, it can be sharp or blunt. Such supports are not hollow, so no holes need to be made to submerge them in the ground. The technology of hammering or vibration pressing into the soil is used. They are widely used in civil engineering, they are also in demand in the construction of a private house (wooden, block, frame).

It looks like a shell, for immersion in the soil of which a well is preliminarily prepared. The support can be round or square, but the latter still has a circular cross-section. Hollow supports, in turn, are divided into solid and composite (they consist of several elements that are assembled immediately before immersion).

But it is also mounted by immersion in a previously prepared recess.

Depending on the type of reinforcement, reinforced concrete piles are of the following types:

• supports with non-tensioned longitudinal reinforcement with transverse reinforcement;
• Supports with prestressed longitudinal reinforcement with or without transverse reinforcement.

If we talk about the shape of the cross-section of the piles, then they are round (hollow or solid), square, square with a round cavity, rectangular. It is unacceptable to place supports with a square cross-section in permafrost soil. Even with a slight thawing, the pile will roll and the building will skew. In regions with increased seismic activity, structures with a circular cross-section should be used.

Allocate one-piece and prefabricated structures. The second ones consist of several segments, which makes it possible to increase the height of the product. The segments are fixed by welding or by means of a bolt connection.

The installation of piles is preceded by geological surveys and soil sampling at different times of the year. Based on the results obtained during the analysis, a decision is made on the methods of pile driving. And also project documentation is drawn up, in which, among other data, the bearing load is calculated for one pile element, their size and number are determined.

The next step is a trial driving of the support, which allows you to evaluate how the support behaves in practice. After driving, it is left for some time (from 3 to 7 days), during which observations are also conducted.

To drive the piles, dynamic and static forces are applied - blows are applied to the support surface with a special hammer. To prevent the destruction and deformation of the elements at this moment, the headbands, which protect the head of the base during impact, allow.

If the installation is to be carried out in water-saturated soils, it is better to use a vibratory pile driver. The installation process is a sequential raising and subsequent lowering of the pile into the soil. These cycles are repeated until the base of the element reaches the design depth.

If the installation is supposed to be on extremely dense and hard soils, it is possible to combine the method of driving and vibration immersion with soil erosion. To do this, water is pumped into the well along the pile under pressure. It reduces friction between the element and the soil, softening the latter.

The method of driving and vibrating is applicable for solid and shell supports, but is not suitable for construction in urban conditions, since it is accompanied by strong noise and vibrations. The latter can negatively affect the state of the foundations of neighboring objects.

Hollow and rammed piles are installed using drilling technology, which provides for preliminary preparation of the mine. A support is introduced into it, and a primer or cement-sand mortar is poured between its walls and the side surfaces of the mine.

Drilling installation technology has several varieties. So, for clay soils, the bored method is suitable, in which a hollow pile is lowered into the well and concreted directly in the ground. In addition, ready-made reinforced concrete piles can also be used, the fixation of which in the well is carried out by backfilling between the side surfaces of the base and the walls of the shaft with clay solution. Instead of the latter, casing can be used.

Drilling methods involve injecting fine-grained concrete mortar into the well, while drilling methods involve filling the space between the well and a pile of concrete mortar placed in it.

Piles are produced by large factories or production workshops at construction firms.As a rule, the products of the former have a lower cost, but factories prefer to cooperate with wholesale buyers.

If you need a limited number of supports, it is best to contact the workshop at a reputable construction firm. As a rule, here you can order piles at least by the piece, but their cost will be higher. This is due to the fact that small companies cannot build up their power, therefore they increase their own revenues by increasing the price list.

Choosing piles is better than domestic production, since they are manufactured in compliance with the requirements of GOST.

Usually the price of a pile depends on its length and cross-sectional dimensions, as well as the grade strength of the concrete used. The lowest cost is possessed by three-meter structures with a square section, the side of which is 30 cm.

As a rule, the larger the batch of purchased concrete products, the lower the cost of one unit of goods. When registering a self-pickup, a discount is also provided in most cases.

You will learn more about reinforced concrete piles in the following video.