For the construction of residential and industrial buildings, various types of foundations are used, but the pile-grillage construction deserves special attention. It is usually chosen in those cases when sharp changes in relief, heaving and weak soil are observed on the land plot. This type of foundation is also well suited for the development of localities 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 in a single structure. Its device can be either with a monolithic type of bookmark (covered with a stove), or built with 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 option, it is formed from a concrete frame, in which the height of the platforms is leveled by piles of different lengths.
Since piles are used during laying of the foundation, buried in the ground between the bearing layer and the lower level of freezing, it is difficult to distribute the building load between them. Therefore, often the pile-grillage foundation is made of prefabricated channel and timber. All supports of this design are mounted in a unit using special tapes and concrete. It is worth noting that the combination of grillages and piles gives the supporting base reliability and stability.
Depending on which foundation is laid (wooden, metal, concrete or reinforced concrete), the building base acquires different technical characteristics. According to the requirements of SNiP, construction of structures with low and high grillages, which are located above ground level, is allowed. They are usually made of metal pipes of large cross-section or of concrete. At the same time, it is much more difficult to make grillages from concrete, since it is necessary to accurately calculate the place of filling of the tape from the soil.
The main feature of the foundation is the fact that the grillages included in its device can withstand uneven loads, providing the base with rigid coupling. The grillages redistribute the load, as a result of which the already “leveled” weight of the building is transferred to the piles, and the structure is protected from the formation of cracks in the walls.
Unlike other types of foundations, the pile-grillage foundation ideally distributes the bearing loads from the building to the ground, so choosing it, you can be sure that the new building will last more than several decades and will be protected not only from sudden changes in temperature, but also from seismic activity. Such designs are widely used for both public and individual construction. Especially suitable for sites located on a slope with heaving permafrost soil and complex terrain.
In addition, such foundations are recommended:
- for building a brick house;
- in frame construction;
- for structures of gas silicate blocks;
- on soils with increased density;
- with high groundwater distribution;
- on unstable soil with quicksand.
The pile-grillage design also allows you to lay the floors directly on the ground without additional surface leveling and pouring a deep tape, since piles of different heights compensate for all irregularities, eliminating the difference in height. You can use such a foundation in the construction of buildings with a weight exceeding 350 tons - it will turn out much more reliable and economical than a tape or tile base. But in this case, it is necessary to lay in the project an increased safety factor, which should not be 1.2, as usual, but 1.4.
Advantages and disadvantages
Pile-grillage foundation is a single system consisting of 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 is characterized by some advantages.
- High economic benefit. Installation does not require large financial costs, since land work is minimized.
- Sustainability. The large bearing capacity makes it possible to erect multi-storey buildings using heavy construction materials in their decoration.
- Extended construction coverage. Compared with other types of foundations, territory development can be performed on any type of soil that is not suitable for laying traditional foundations. The difficult geometry of the landscape, slopes and slopes are not an obstacle to work.
- Possibility of forming piles separately from grillage. Thanks to this nuance, concrete mix is significantly saved. In addition, you can use both ready-made and self-prepared solution.
- Convenient arrangement of piles with cable lines and underground pipelines. This simplifies the creation of the project and does not violate the functionality of the settings.
- High strength. A monolithic bunch of grillages and supports protects the structure from shrinkage of the soil, 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 foundation pit, which simplifies the construction process.
- Good thermal insulation. The space between the ground and the base due to the increased arrangement of the grillage does not allow cold air flows - this reduces heat loss and makes the building warm.
- No risk of flooding. Pile structures, elevated above the surface of the earth up to two meters, protect the structure from possible flooding.
- Easy to install. With minimal construction skills, it is quite realistic to build such a foundation with your own hands, without resorting to the help of craftsmen or using earth-moving devices.
- Short terms of work.
The above advantages are relevant only if the installation of the base is carried out in compliance with all construction technologies, and the building is operated in accordance with the loads calculated for it.
In addition to the advantages, this type of foundation has its disadvantages:
- The impossibility of building on stony soil - solid 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 sag, otherwise the stability of the supports will be violated, and the soil will fail.
- For buildings, the construction of which is planned in harsh climatic regions with low temperature, it is necessary to think over additional measures for laying high-quality thermal insulation.
- Such grounds are not provided for the implementation of projects of houses with a basement and a basement.
- The complexity of calculating the bearing capacity of the supports. It is difficult to independently calculate this indicator. In case of the slightest inaccuracies, the foundation may skew, and as a result, the geometry of the entire structure will change.
Despite the shortcomings, the pile-grillage foundation proved to be good among builders and received only positive feedback from house owners.
The supports used in the construction of the pile-grillage foundation 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. Work is carried out manually or using special equipment. So that the design on the screw supports is strong, and the pipes are 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 printed foundation has high strength.
- Reinforced concrete. Installation is carried out using ready-made reinforced concrete supports arranged in the well.
- Clogged. As a rule, such grounds are chosen for the construction of large facilities. Supports are clogged using special equipment, after which concrete mortar is poured.
In addition, the foundation may differ in the depth of the grillage and it happens:
- raised above the ground to a height of 30 to 40 cm.
A recessed grillage is usually used when installing piles designed for heavy structures of aerated concrete or brick. In this case, an additional strapping is performed by the stove, and the foundation can serve as the basement of the building. As for the construction of wooden structures, the foundation with a raised grill is ideally suited for them - this saves money on building material, and the raised building will protect against soil heaving.
Design and Calculation
An important point before laying the foundation is its accurate calculation. To do this, create a project and plan for the future building. Then a drawing of the base is drawn, and the pattern of laying the piles is necessarily indicated, given their location at the intersection 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, it is necessary to calculate the area of piles - for this purpose, their quantity is first determined, the minimum height and thickness are selected.
For correct calculations, you must also 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";
- reference area - using the known weight of the structure and the reliability coefficient, the load on the supports is easily determined;
- dimensions and cross-sectional area of piles - thanks 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 a previously defined 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 base to serve reliably, during the work, special TISE technology and step-by-step installation instructions should be used.
The construction of a pile-grillage foundation provides for the following works:
- foundation calculation and project creation;
- preparation and layout of the construction site;
- drilling and digging trenches;
- formwork formation;
- pouring with concrete mortar and rigid sealing of joints.
Each of the above items is important, therefore, at each stage of construction, quality control should be checked, since the slightest mistake or inaccuracy will then adversely affect the operation of the building.
Before starting construction workplace is carefully prepared. To do this, first of all, the site is cleaned of mechanical obstacles in the form of stones, roots and trees. Then the ground is well leveled and the fertile layer is removed. After this, markings are applied indicating the location of the piles. The work is performed using a cord and wooden stakes.
Markings need to be set strictly along the diagonals. Cords are pulled to mark the inside and outside of the walls. If inaccuracy is allowed, deviations from the design will be obtained, and the foundation during operation may be distorted.
In the event that small elevation changes are observed on the site, marking is easy to perform. For areas with difficult terrain, the help of experienced craftsmen will be required. Particular attention should also be paid to the corners of the building - they should be at an angle of 90 degrees.
Once the boundaries of the foundation are determined, you can begin excavation. First, they dig a trench under the grillage, then drill holes in which piles will later be installed. The work is usually carried out with the help of such a hand tool as scrap, shovel and drill. If financial opportunities 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 households, the acceptable indicator is 0.25 m, for mobile - 0.5 m, and for residential buildings this figure rises to 0.8 m. As for the depth, the grillage can lie 0.7 m.
In a dug ditch, it is necessary to check the bottom and walls for evenness - this will help the laser level. After that, a sand cushion rests at the bottom of the trench, sand is selected in large fractions. After laying, the surface is moistened with water and carefully tamped. The sand cushion cannot be less than 0.2 m. The next stage of excavation will be the preparation of holes for vertical piles: the holes are drilled 0.2-0.3 m deep.
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 grillage. Most often, a metal element is chosen for work, which is easily welded to the heads of piles. In order for the structure to transmit loads evenly, it must be placed horizontally. In the event that the construction of the foundation of the project involves the use of a reinforced concrete low grillage, then additionally fill out the 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 calculated in accordance with the indicators of the cap. The installation of the stops and the assembly of the shields in many ways resembles the technology of work for the 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 emerging from the piles are bent: one row is tied to the upper belt, and the other to the lower.
Rebar outlets should not be less than 50 mm from the diameter of the rods. For example, if you use reinforcement with a cross section of 12 mm, it is recommended to bend it by 60 mm.
Stacking embedded parts
After all the work on the manufacture of the frame is completed, you need to consider the placement of communication systems. For this, boxes and pipes are laid through which sewage, electricity, water supply and heating will pass. We must not forget about laying pipes for engineering systems and products. If this step is not performed, then after construction for installation work it will be necessary to hammer concrete, which may violate its integrity and damage the building.
The final step in the installation of the foundation is the pouring of concrete. For concreting, cement M300, 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 additionally vibrated. Thanks to this, the surface is durable and uniform.
First of all, holes intended for 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 the appearance of bumps and air bubbles is possible. 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, concrete will gain strength and become ready for subsequent construction work.
Sometimes the laying of the base is carried out at a temperature below + 10C - in this case, you will have to wait for complete drying for at least 2 weeks. In the winter season, the poured concrete will need to be additionally heated and insulated.
The pile-grillage foundation must be built correctly, adhering to all construction technologies, this will help to increase its technical and operational characteristics.
If construction work is performed by beginners, then they need to consider some recommendations from experienced professionals.
- Installation should begin with calculations. For this, the type of soil and the depth of the grillage are determined. With insufficient depth of the laying of the support, the building can shrink and crack, and then even collapse.
- A huge role is played by soil research, on which the bearing capacity of a structure depends. The largest indices are rock and rocky soils. If the composition of the soil is incorrectly determined, this will lead to errors in calculating the load of the structure, as a result of which it will sink into the ground.
- There should be a good connection between the piles and the grillage, since under the influence of soil pressure an unstable structure can collapse.
- Regardless of the type of foundation, a sand cushion should be laid on the depth of freezing - this is especially true for the operation of the base in the winter. Frozen soil can expand and cause tearing of the grillage.
- The grillage should not come into contact with or be buried in the ground. 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 in concrete.
- It is necessary to accurately calculate the step between piles. This indicator is determined in accordance with the load on the foundation, diameter and amount of reinforcement.
- During the reinforcement, it is worthwhile to provide the right amount of ventilation ducts. All internal compartments must be connected to the exits to the street.
- A huge role in the construction of the base is played by insulation and waterproofing. They should be laid before pouring concrete into the foundation.
- The bottom of the pit or trench must be rammed and not loosened. It should not be allowed for the ground to crumble from the walls. In addition, sedimentary waters must leave the trench or foundation pit, otherwise the bottom will get wet and will be unsuitable for pouring the solution. Excessive steepness of slopes is also unacceptable in trenches.
- Weak soil requires reinforcement with piles and good backfill.
- The sand, which is used to fill the air cushion, must be moistened and the cushion distributed under the contour into the edge at an angle of 45 degrees.
- The formwork must be reliably fixed, since when pouring 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 specified in the project.
- When reinforcing the framework, 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 a smooth reinforcement that does not have traces of rust, dirt and paint.
- It is undesirable to fix fittings by welding - this may violate its strength at the joints.
- The brand of concrete for pouring should be chosen depending on the construction of the base and the climatic conditions of the region.
About what are the structural features of the pile-grillage foundation, see the following video: