Pile-grillage foundation: design features and installation technology

For the construction of residential and industrial buildings, various types of foundations are used, but the pile-grillage structure deserves special attention. It is usually chosen in cases where there are sharp drops in relief, heaving and weak soil on the land. This type of foundation is also well suited for buildings in areas located in the permafrost zone.

The pile-grillage foundation is a reinforced concrete, wooden or steel base, poured with concrete, in which all the elements are connected into a single structure. Its device can be either with a monolithic type of bookmark (covered with a slab), or built using a hanging grillage. The hanging foundation is characterized by an open gap between the soil surface and the grillage; it must be additionally insulated and covered with waterproofing. As for the monolithic version, it is formed from a concrete frame, in which the height of the platforms is leveled by piles of different lengths.

Since during the laying of the base, piles are used, buried in the ground between the bearing layer and the lower level of freezing, it is difficult to distribute the load of the building between them. Therefore, the pile-grillage foundation is often made prefabricated from a channel and a bar. All supports of this design are attached to the assembly using special tapes and concrete. It is worth noting that the combination of grillage and piles gives the load-bearing foundation reliability and stability.

Depending on what kind of foundation is being laid (wooden, metal, concrete or reinforced concrete), the base for building acquires different technical characteristics. According to the requirements of SNiP, it is allowed to build structures with low and high grillages, which are located above ground level. They are usually made from large metal pipes or concrete. At the same time, making concrete grillages is much more difficult, since it is necessary to accurately calculate the place of pouring the tape from the soil.

Unlike other types of foundations, the pile-grillage foundation ideally distributes the bearing loads from buildings to the ground, so choosing it, you can be sure that the new building will reliably serve for more than a dozen years and will be protected not only from sudden temperature changes, but also from seismic activity. Such structures are widely used for both public and individual construction. Especially suitable for areas located on a slope with heaving permafrost soil and difficult terrain.

In addition, such foundations are recommended:

• for building a brick house;
• in frame construction;
• for structures made of gas silicate blocks;
• on soils with high density;
• with a high distribution of groundwater;
• on unstable soil with quicksand.

The pile-grillage structure also makes it possible to lay floors directly on the ground without performing additional leveling of the surface and pouring a deep tape, since the piles installed at different heights compensate for all irregularities, eliminating the height difference. Such a foundation can also be used in the construction of buildings with a weight exceeding 350 tons - it will turn out to be much more reliable and economical than a strip or slab base. But in this case, the project will have to include an increased safety factor, which should not be 1.2, as usual, but 1.4.

The pile-grillage foundation is a single system consisting of a grillage and supports.

Due to the presence of a concrete base in the structure, reinforced with reinforced elements, the base acts as a reliable support for buildings and has some advantages.

• High economic benefit. The installation does not require large financial costs, since land work is minimized.
• Stability. The large bearing capacity makes it possible to erect multi-storey buildings using heavy building materials in their decoration.
• Expanded construction coverage. Compared to other types of foundations, land development can be carried out on any type of soil that is not suitable for laying traditional foundations. Difficult landscape geometry, slopes and slopes are not an obstacle to work.
• Possibility of forming rammed piles separately from the grillage. Thanks to this nuance, the concrete mix is ​​significantly saved. In addition, you can use both ready-made and self-prepared solution.

• Convenient location of piles with cable lines and underground pipelines. This simplifies project creation and does not break the functionality of the settings.
• High strength. The monolithic bond of the grillage and supports protects the structure from soil shrinkage, so the structure does not break or deform during operation.
• Lack of preparatory work. To lay the pile-grillage foundation, there is no need to form a pit, which simplifies the construction process.
• Good thermal insulation. Due to the increased arrangement of the grillage, the space between the ground and the base does not allow cold air currents to pass through - this reduces heat losses and makes the building warm.
• No risk of flooding. Pile structures, raised up to two meters above the ground, protect the structure from possible flooding.
• Easy to install. With minimal construction skills, it is quite possible to erect such a foundation with your own hands, without resorting to the help of masters and without using earth-moving devices.
• Short terms of work.

In addition to the advantages, this type of foundation also has disadvantages:

• Impossibility of building on rocky soil - hard mineral rocks make it impossible to install piles.
• Problematic installation in areas with horizontal displacement. It is not recommended to carry out work on soils that can sink, otherwise the stability of the supports will be disturbed, and the soil will fall through.
• For buildings planned for construction in harsh climatic regions with low temperatures, additional measures will have to be taken to install high-quality thermal insulation.
• Such grounds are not provided for the implementation of projects of houses with a basement and a ground floor.
• The complexity of calculating the bearing capacity of the supports. It is difficult to calculate this indicator on your own. In the case of the slightest inaccuracies, the foundation can be skewed, and as a result, the geometry of the entire structure will change.

Despite the shortcomings, the pile-grillage foundation has proven itself well among builders and received only positive reviews from home owners.

The supports that are used in the construction of the pile-grillage base are selected in accordance with the load of the building, the type of soil and climatic conditions. They can be made both from metal, concrete, wood, and from combined materials.

Therefore, depending on the characteristics of the piles and the method of their installation, some types of foundation are distinguished.

• Screw. It is made from hollow metal pipes with an open end. The works are carried out manually or with the help of special equipment. To make the structure on screw supports strong and the pipes protected from oxidation, their hollow part is poured with a solution.
• Bored. It is formed on a land plot by pouring concrete into a previously prepared reinforced well located on driven piles. The rammed foundation is highly durable.
• Reinforced concrete. Installation is carried out using ready-made reinforced concrete supports arranged in the well.
• Hammer. As a rule, such bases are chosen for the construction of large objects. The supports are hammered using special equipment, after which a concrete solution is poured.

In addition, the foundation may differ in the depth of the grillage and it happens:

• buried;
• terrestrial;
• raised above the ground to a height of 30 to 40 cm.

Recessed grillage is usually used when installing piles intended for heavy structures made of aerated concrete or brick. In this case, additional strapping is performed with a slab, and the foundation can serve as the basement of the building. As for the construction of wooden structures, a foundation with a raised grillage is ideal for them - this saves money on building material, and the raised building will protect against heaving of the soil.

An important point before laying the foundation is its accurate calculation. For this, a project and a plan of the future building are created. Then a drawing of the base is drawn, and the scheme of pile tabs must be indicated, taking into account their location at the intersections with the piers and in the corners. It is necessary to provide so that the width between the piles is at least 3 m. If the distance to their edge is more than three meters, then additional supports will be required. In addition, the area of ​​the piles should be calculated - for this, first, their number is determined, the minimum height and thickness are selected.

For correct calculations, you also need to know some other indicators:

• the mass of the future building - it is necessary to calculate not only all the finishing materials, but also the approximate weight of the internal "filling";
• support area - using the known weight of the structure and the safety factor, the load on the supports is easily determined;
• dimensions and cross-sectional area of ​​piles - due to the known number of supports, their number can be multiplied by the selected area and get the desired value.

All results must be compared with the previously determined reference area. In some cases, it is necessary to reduce or increase the area of ​​the supports, since their bearing capacity will depend on the diameter and type of soil.

The foundation on piles and grillage is a complex structure, but it is quite possible to make it yourself. In order for such a foundation to reliably serve, during the work, a special TISE technology and step-by-step installation instructions should be used.

The construction of a pile-grillage foundation provides for the following works:

• calculation of the foundation and creation of the project;
• preparation and marking of the construction site;
• drilling wells and digging trenches;
• formwork formation;
• reinforcement;
• pouring with concrete and rigid sealing of joints.

Each of the above points is important, therefore, at each stage of construction, quality control should be checked, since the slightest mistake or inaccuracy will then negatively affect the operation of the building.

Before starting construction, the workplace is carefully prepared. To do this, first of all, the site is cleared of mechanical obstacles in the form of stones, roots and trees. Then the ground is well leveled and the fertile layer is removed. After that, markings are applied indicating the location of the piles. The work is performed using a cord and wooden stakes.

The markings must be installed strictly diagonally. The cords are stretched to mark the inside and outside of the walls. If an inaccuracy is made, deviations from the project will result, and the foundation may bend during operation.

In the event that small differences in elevation are observed on the site, marking is easy to perform. For areas with difficult terrain, you will need the help of experienced craftsmen. Particular attention should also be paid to the corners of the building - they should be at an angle of 90 degrees.

After the boundaries of the foundation have been determined, you can start excavation work. First, a trench is dug under the grillage, then holes are drilled into which piles will later be installed. The work is usually carried out using hand tools such as crowbar, shovel and drill. If financial possibilities allow, then you can order specialized equipment.

Depending on the purpose of the future building and the type of soil, the optimal width of the grillage is chosen. For household objects, 0.25 m is considered an acceptable indicator, for mobile - 0.5 m, and for residential buildings this figure rises to 0.8 m.As for the depth, the grillage can lie at 0.7 m.

In a dug ditch, it is necessary to check the bottom and walls for evenness - a laser level will help with this. After that, a sand cushion lays down on the bottom of the trench, the sand is selected as a coarse fraction. After laying it, the surface is moistened with water and carefully tamped. The sand pad cannot be less than 0.2 m. The next stage of excavation will be the preparation of holes for vertical piles: holes are drilled to a depth of 0.2-0.3 m.

Then pipes are installed in the finished pits, which will play the role of formwork, and the bottom is covered with waterproofing material - this will protect the structure from moisture.

An important point in construction is the installation of the grillage. Most often, a metal element is chosen for work, which is easily welded to the pile heads. In order for the structure to transfer loads evenly, it must be placed strictly horizontally. In the event that the construction of the foundation according to the project provides for the use of a reinforced concrete low grillage, then additionally they are filled with crushed stone of the middle fraction. Crushed stone is poured in several layers of 5 cm and compacted well.

Formwork is placed on the prepared base. The width of its tape should exceed the width of the walls, and the height is counted in accordance with the indicators of the basement. The installation of stops and the assembly of shields in many ways resembles the technology of work for a strip foundation.

As for the reinforcement, in most cases, similar to the construction of the tape, two belts of ribbed reinforcement are made from below and from above. They are tied together with piles. The ends of the reinforcement coming out of the piles are bent: one row is tied to the upper belt, and the other to the lower one.

Reinforcement outlets should not be less than 50 mm from the diameters of the rods. For example, if you use reinforcement with a cross section of 12 mm, then it is recommended to bend it by 60 mm.

After all the work on the manufacture of the frame is completed, it is necessary to think over the placement of communication systems. For this, boxes and pipes are laid through which the sewerage, electricity, water supply and heating will pass.We must also not forget about laying pipes for engineering systems and air vents. If this stage is not completed, then after construction for installation work, concrete will have to be hammered, which can violate its integrity and damage the building.

The final stage in the installation of the foundation is the pouring of concrete mortar. For concreting, cement of the M300 brand, crushed stone and sand are usually used. The mixture is prepared in a ratio of 1: 5: 3. At the same time, the solution is not just poured - it is also vibrated additionally. Thanks to this, the surface is durable and homogeneous.

First of all, the holes intended for the piles are poured with concrete, and then the formwork itself. It is advisable to complete the workflow in one go. If concreting in stages, then irregularities and air bubbles may appear. The optimum temperature for pouring is considered to be + 20C - with this indicator, the formwork can be removed after four days. During this period of time, the concrete will acquire strength and become ready for subsequent construction work.

The pile-grillage foundation must be erected correctly, adhering to all construction technologies - this will help to increase its technical and operational characteristics.

If construction work is carried out by novice craftsmen, then they need to take into account some of the recommendations of experienced specialists.

• The installation should start with calculations. For this, the type of soil and the depth of the grillage are determined. If the support depth is insufficient, the building can shrink and crack, and then even collapse.
• A huge role is played by the study of the soil, on which the bearing capacity of the structure depends. The highest indicators are found in rocks and stony soils. If the composition of the soil is determined incorrectly, this will lead to errors in the calculations of the load of the structure, as a result of which it will sink into the ground.
• There must be a good connection between the piles and the grillage, since the unstable structure can collapse under the influence of soil pressure.
• Regardless of the type of foundation, it is imperative to lay a sand cushion at the depth of freezing - this is especially true for the operation of the foundation in winter. Frozen ground can expand and cause the grillage to break.

• The grillage should not touch the surface of the ground or be buried in it. It is necessary to remove a small layer of soil around the entire perimeter of the site, then install the formwork, fill in the sand and pour concrete.
• The step between the piles should be accurately calculated. This indicator is determined in accordance with the load on the foundation, the diameter and the number of reinforcement.
• During the reinforcement, it is worthwhile to provide for the required amount of ventilation ducts. All internal compartments must be connected to outside exits.
• Insulation and waterproofing play a huge role in the construction of the base. They should be laid before the foundation is poured with concrete.
• The bottom of the pit or trench must be tamped down and not loosened. It should not be allowed that earth from the walls crumbled onto the base. In addition, sedimentary water must flow away from the trench or foundation pit, otherwise the bottom will get wet and be unsuitable for filling with a solution. Excessive slope steepness is also unacceptable in trenches.
• Weak soil requires reinforcement with piles and good backfill.

• The sand that is used to fill the air cushion must be moistened and the cushion must be distributed under the contour to the edge at an angle of 45 degrees.
• The formwork must be securely fastened, since when poured with concrete, it may not withstand the load and collapse. The deviation of the formwork from the vertical by more than 5 mm is not allowed.
• The height of the foundation is made with a small margin of 5-7 cm from the height indicated in the project.
• When reinforcing the frame, it is recommended to use rods with a total cross-sectional area of ​​at least 0.1% of the area of ​​the concrete element. In this case, it is best to choose smooth fittings that do not have traces of rust, dirt and paint.
• It is undesirable to fasten the reinforcement by welding - this can violate its strength at the joints.
• The grade of concrete for pouring should be chosen depending on the construction of the base and the climatic conditions of the region.

For information on the design features of the pile-grillage foundation, see the following video: