What are grillages for pile foundations? We easily and quickly build a pile-grillage foundation: pros and cons, arrangement technology What is a pile foundation with a grillage

When solving problems of ensuring the stability of erected buildings, builders assign a serious role to the strength of the foundation. The construction of buildings is carried out on various types of foundations. For problematic soils, a column-pile foundation is preferable, consisting of individual supports that transfer the load to the soil. Reliable fixation of the heads of the supporting elements is ensured by the grillage. Many have heard this term, but not everyone has an idea about the purpose of the design, advantages and classification.

What is a grillage in construction

Among the various types of foundations, grillage is widely used. Grillage - what is it? This question is often asked by novice builders. Let's figure out what the grillage base of the building is. Experienced developers, when implementing, combine the upper parts of the supports with horizontally located beams. As a result, a single power circuit is created - a grillage, which has increased strength and rigidity. In the formed foundation, the load from the mass of the structure is carried by pile supports of the grillage structure.

The main purpose of the power harness:

• ensuring a fixed position of foundation supports;
• uniform distribution of loads transmitted by the building to the columns.
• formation of a reliable supporting surface for the construction of walls and partitions.

Grillage is a horizontally located part of a pile foundation that receives and transmits the load from the walls of the building to the piles

A similar structure, consisting of screw or reinforced concrete piles united by a horizontal belt, is widely used in the construction of one-story buildings on various types of soil, including soils with a high concentration of clay particles, sand and moisture.

The grillage base has a set of serious advantages:

• allows the construction of buildings on problematic soils;
• ensures the stability of buildings;
• does not require labor-intensive excavation activities;
• does not depend on the depth of the aquifers.

Along with its advantages, the pile-grillage foundation also has weaknesses:

• the complexity of the construction of the basement, the main dimensions and dimensions of which are related to the design of the grillage and the height of the protruding parts of the supports;
• the need to use special equipment to install the supporting elements of the foundation base into the ground.

When constructing pile foundations, in order to increase their load capacity, it is advisable to combine the protruding parts of the supports with a force belt. After all, the foundation is loaded with the weight of the roof, walls, ceiling, and household appliances. Estimates for the construction of a grillage base are always lower than for the construction of a strip foundation.

Depending on the type of foundation and the geological structure of the soil, the grillage may differ

When understanding what a grillage is in construction, study its classification. The grillage foundation is classified according to the following criteria:

• location level;
• the material used for construction;
• design features.

Let us dwell in detail on the features of each type of grillage.

Types of grillage by location

When planning to build a grillage foundation for a frame house with your own hands, decide on the level of location relative to the zero mark.

The following options are possible:

• hanging foundation belt;
• towering grillage;
• shallow base.

Let's look at each variety.

Rising above ground level

A distinctive feature of a high grillage is the location of the bottom of the tie belt above the ground surface at a distance of 10–15 cm, which allows:

• build a raised grillage base on problematic soils;
• eliminate the influence of frost heaving forces in the soil;
• avoid the development of dampness by ventilating the space under the building;
• maintain the position of the foundation supports during movements of soil layers.

The raised grillage is the most common and involves the location of its sole at ground level

There is another serious advantage of the rising power contour - a gravel-sand cushion for the foundation of a high structure is not required, since it is located above the zero level and does not contact the soil.

Design disadvantages:

• increased level of heat losses due to the penetration of cold air masses under the building’s foundation;
• the need for enhanced thermal insulation of the floor in contact with cold air;
• increased level of costs associated with the need to install protective shields of a decorative base along the contour of the building.

If you want to build a high grillage belt, figure out how to properly protect the lower part of the building and the floor from cold air currents.

Located at zero

The grillage base, located at the same level with the soil, is erected quite often. The binding belt is based on a sand-crushed stone cushion with a thickness of 15–20 cm. Backfilling is carried out after the soil has been removed under the lower plane of the grillage. The main feature of the design is the damping cushion.

Refers to this type if its sole coincides with the soil level mark

She performs important tasks:

• prevents the negative impact of frost heaving of the soil;
• does not allow melt water and sediment to accumulate under the grillage base;
• seals the gap under the horizontal beam of the grillage.

To increase the strength characteristics of the structure and protect it from moisture, waterproofing is also performed. It’s easy to make a raised grillage with your own hands. Step-by-step instructions will help you cope with the task.

Buried in the soil

The power structure connecting the upper parts of the supports is located below the zero mark. The construction technology involves the following work:

1. Preparation of a pit located between the support columns.
2. Leveling the base of the trench.
3. Adding a gravel bed.
4. Installation of panel formwork.
5. Assembly and installation of reinforcement grid.
6. Pouring concrete solution.

They are concreted during the process of pouring the load-bearing frame. To increase the service life of a buried grillage, it is important to reliably protect it from the influence of precipitation. Figure out how to do it right. Concrete edging along the contour of the house, made with a slope, will ensure effective removal of moisture from the grillage foundation.

The main difference between this option is the location of the tape below ground level

Classification of grillage according to the type of building material used

Let's consider what material a grillage can be made from. Various building materials are used to make grillage frames:

• concrete reinforced with reinforcing mesh;
• rolled metal of various sections;
• dried and processed wood;
• branded concrete without reinforcement.

The strength characteristics of the structure must correspond to the calculation of the pile grillage. Let us dwell on the features of using various materials.

Monolithic reinforced concrete grillage

In terms of performance characteristics, reinforced concrete structures are stronger than concrete ones.

The reinforced concrete grillage, thanks to its durable reinforcement grid, has the following advantages:

• increased load capacity;
• long period of operation;
• high level of reliability;
• sufficient rigidity;
• ability to withstand increased compressive loads.

For reinforcement, steel rods connected into a common frame, as well as ready-made spatial gratings, are used.

A monolithic grillage is a one-piece structure that is poured directly on the construction site

Metal construction

A power belt made of rolled metal allows us to provide the required safety margin. The construction technology involves performing the following operations:

1. Cutting blanks from channel or I-beam.
2. Installation of profiled steel at the ends of columns.
3. Welding individual beams into a common contour.

Apply a protective coating to improve corrosion resistance.

Wood grillage base

The strength of wood allows it to support the mass of light wooden or frame buildings. To ensure the durability of wooden beams:

• dry the material thoroughly;
• saturate the wood with antiseptics;
• waterproof the surface of the beams with roofing felt.

The service life depends on the quality of the material preparation.

Concrete grillage

The sequence of actions for arranging a grillage foundation made of concrete is similar to the construction of a reinforced concrete belt. The main difference is the concreting of the load-bearing frame without reinforcement cages. The susceptibility of concrete to tensile forces and bending moments limits the range of use of a concrete grillage.

Structural types of foundation with grillage

The classification provides for the division of grillages into types depending on the design. Possible options:

• prefabricated structure. Consists of profiles welded together. The service life is limited to two decades due to insufficient rigidity. The prefabricated version is used for temporary buildings;
• one-piece grillage. It is formed from concrete mortar reinforced with a reinforcement cage. Ensures the stability of low-rise buildings on problematic soils;
• combined version of the grillage base. Includes factory-fabricated components. They are assembled into a single load-bearing frame and concreted. The design is used in industrial construction.

The choice of the optimal option is determined by the requirements of the project.

The grillage is a loaded part of the foundation that increases the rigidity of the structure. The classification allows you to select the required type of tie belt depending on the structural features and soil characteristics. When deciding on the grillage design, listen to the opinions of professionals.

Do-it-yourself pile-grillage foundations are most in demand among owners of suburban areas. In dense settlements, it is impossible to use heavy special equipment (hammers, pile drivers) for driving driven piles with a design length of more than 10 m or for light buildings. Renting this equipment is expensive, so short suspended bored piles with a monolithic grillage are used.

Due to the variety of construction technologies and materials used for pile-grillage foundations, there is a special terminology:

• base - a layer that absorbs vertical loads and lies below the freezing mark;
• pile - a vertical structure made in the soil or immersed in it;
• pile field - a group of piles for one structure, building;
• grillage - a monolithic or beam structure along the heads of piles (slab, lattice, frame or beam);
• low grillage - buried in the soil or located at the level of the zero mark;
• high (hanging) grillage – raised above ground level;
• bearing capacity of a pile is the sum of soil resistances on the side surfaces and under its lower end.

Based on material, bored piles are classified as follows:

• composite - reinforced concrete inside steel or polymer permanent formwork (large diameter pipe);
• rubble concrete - in the lower part of the pile stones are sunk into concrete (maximum size 15 cm, strength not lower than the design grade of concrete), the upper part (0.5 - 0.7 m) is filled with clean concrete, reinforcement is usually along the entire length (except for backfill);
• reinforced concrete - the pile is poured entirely from concrete with reinforcement along the entire length (usually not stressed);
• concrete - reinforcement only in the upper part for piping with a grillage.

The pile shaft can be manufactured in several ways, even using the same materials. For example, if a hole in the ground with a reinforcement cage placed inside is filled with concrete, the pile will be shellless.

Scheme of a pile with expansion - TISE.

If the pile reaches the bearing layer, is poured into a polymer or metal pipe, which does not carry loads and remains in the well for the entire period of operation (non-removable), acting as waterproofing, a pile with a shell is obtained.

If the temporary formwork is removed after pouring, the pile is called a temporary shell, the method is a vertically moved VPT pipe. If the formwork remains inside the well and performs load-bearing functions, the pile is called a pipe-concrete pile.

To increase the load-bearing capacity, the base of the pile can be widened with a monolithic base. The base is drilled out with a special tool, an explosion or concrete piles. In a general grillage, the head of a bored pile can have a sliding mate or a rigid embedment into a monolith.

If, during geological exploration of the site, the occurrence of a bearing layer deeper than 3 m is revealed, bored piles-racks will cost an individual developer more than a screw foundation SVF or a floating slab. In this case, suspended piles are more effective, the bearing capacity of which depends on the density and porosity of the soil. If the frictional forces on the side surfaces are not enough, other foundation options should be considered.

Unlike a strip foundation, the depth of the grillage does not depend in any way on the characteristics of the soil:

• the tape rests on the ground with its sole, there are lateral shear loads from heaving forces;
• The grillage does not rest on the ground, it is created solely for tying piles, distributing loads, and supporting wall materials (especially important for foam blocks and bricks).

After pouring the monolithic grillage, an air layer is created between the soil and its base to compensate for heaving forces. In low grillages, it is protected on the sides with sheet materials to prevent the soil from shedding and filling this space with heaving soil.

Taking into account the above, a monolithic grillage along the heads of bored piles is effective in the following cases:

• lightweight buildings - budget savings of 30 - 50% in comparison with a slab, strip foundation for log houses, half-timbered, frame, panel (SIP technology), panel cottages;
• complex terrain - slopes with a height difference of more than 1.5 m in the building area;
• high groundwater level - piles can be poured into the shell with a slight rise in water or by temporarily pumping it out of the well;
• swamp, coastal zone - excavation work for other types of foundations is impossible.

Piles are economically effective in individual construction only at a depth of 3–5 m, which is usually sufficient for lightweight structures. With normal geology on flat areas, piles reduce the construction budget of brick and concrete buildings by half. Only in this case does the foundation comply with the requirements of SP 24.1333, which regulate the design of pile foundations.

Step-by-step instructions using the example of a monolithic grillage on bored piles

To build a foundation of this type, an individual developer needs to determine the main dimensions of the elements: cross-section of the grillage (height, width), depth of the well, parameters of the reinforced belt, type of formwork. After which, the amount of building materials is calculated. For convenience, below are step-by-step instructions describing the key points.

Geological surveys, calculation of parameters

Unlike screw piles, for which it is often enough to test screw in a building spot in several places to determine the depth of the bearing layer, this will require full-fledged geological surveys. According to SP 24.1333, this will require a set of operations:

• soil testing with static loads;
• pessiometry, dynamic and static probing;
• laboratory analysis of groundwater, soils from different layers during drilling 3 m below the design level.

In addition, specialists will take into account the impact of piles on nearby buildings and the environment. The result of the research is a geological section in which the thickness of each layer of the layers of different rocks present in the building area is visible. This allows you to select from the corresponding SP tables the standard values ​​of the bearing capacity of clay, sand, and loam to calculate the bearing capacity of the pile.

For example, for soil conditions of 2 m refractory loam, 1 m hard loam, on top of wet sand, there are several options for drilled piles:

• A – the depth of the piles is more than 3 m (passing through loam with the base resting on the sand), diameter 0.5 m;
• B – depth 3 m, diameter 0.4 m;
• B – depth 2 m, diameter 0.5 m.

For reinforcement, rods of 10–12 mm of periodic section are used. The clamps are bent from 6–8 mm of smooth reinforcement. For tying, it is better to use annealed wire. The pitch of the horizontal clamps is 30 - 60 cm, the rods should protrude 30 - 40 cm above the heads. After stripping, they are bent at right angles parallel to the axes of the walls and connected to the lower belt of the grillage.

Pouring and waterproofing

The formwork for the grillage begins to assemble from below.

Due to the large volumes of concrete work, a pile-grillage foundation is usually poured in stages. First, the mixture is placed in pile formwork and compacted with an in-depth vibrator or reinforcing bars to remove air. The grillage formwork is installed after the piles have gained at least 50% strength (3 – 5 days after pouring). The technology looks like:

• deck installation - only for a hanging grillage, holes are cut in the shield according to the size of the piles, it is put on the heads, supported by H-shaped posts along the entire length;
• installation of side panels - attached to the deck, propped up with bars or pins, the top side should be 5 - 7 cm higher than the design mark;
• reinforcement - two belts of 10-16 mm bars of periodic cross-section reinforcement, fastened with 6-8 mm clamps, bend at the corners, at the junction of the walls.

Grillage reinforcement.

Filling occurs according to standard technology with laying and vibration compaction of the mixture. The entire formwork must be filled in one go. Caring for concrete consists of protecting it from waterlogging (covering it with a film from rain), drying out (sand or sawdust on the top edge of the grillage with periodic moistening in the first three days).

This is done after stripping the grillage in several ways:

• impregnation with penetrating compounds (the service life is similar to concrete structures, no repairs are required);
• coating with bitumen mastics (resource 15 – 30 years, budget option);
• gluing with roll materials (lifespan of glass hydroisol is 30 - 50 years, the need to seal joints, use 2 - 3 layers).

Preferable impregnation waterproofing or a set of measures according to the last two options (coating + gluing).

Blind area and storm drain

For any foundation, regardless of its design, a blind area is required that has a 4–7 degree slope from the building outward. This structural element allows rain and melt water to be drained away from concrete structures under a monolithic low grillage and under a high grillage. To prevent runoff from destroying the soil adjacent to the blind area (usually the fertile layer), stormwater inlets (receive water from the roof drain) and trays that transport liquid to a separate underground reservoir are integrated into its outer perimeter.

To reduce the heaving forces under the monolithic grillage, which exert pull-out loads on the piles, at a depth of 40–70 cm. To do this, extruded XPS polystyrene foam is laid at the bottom of the trench. The width of the blind area should be 5–10 cm larger than the projections of the roof slopes, so that when the roof gutters overflow, the water does not destroy the fertile layer.

The standards SP 71.13330 of 2011 recommend a blind area width of 0.7 - 1 m for sandy, clayey soils, respectively, with a tight connection to the backfill (false base) of the pile-grillage foundation. It is made of waterproof material:

• concrete screed 5 cm thick in the thinnest areas;
• paving slabs/paving stones;
• rubber or PVC tiles;
• composite decking.

A budget option is a blind area made from dry asphalt concrete mixtures, used for repairing roadways and lining garden paths. It is compacted with a tamper, does not require heating or melting, and increases strength over time.

Following the recommendations given, even an individual developer without special education will be able to produce a pile foundation with a monolithic grillage with a minimum budget without errors. When properly calculated, the service life of underground structures is not inferior to other types of foundations, maintaining high maintainability and the possibility of increasing the usable area during operation.

Advice! If you need contractors, there is a very convenient service for selecting them. Just send in the form below a detailed description of the work that needs to be performed and you will receive proposals with prices from construction teams and companies by email. You can see reviews about each of them and photographs with examples of work. It's FREE and there's no obligation.

The foundation on bored piles, with a widening at the base - a “heel” and hanging above the ground, is popular among FORUMHOUSE participants. The availability of technology and the possibility of independently manufacturing this type of base are reflected.

However, as with any construction, certain features must be taken into account when constructing one. In this regard, the practical experience and “tricks” of the users of our portal, which they use when building such a foundation, are interesting.

Vzik User FORUMHOUSE

I already have a house made of aerated concrete, a bathhouse, a gazebo, a garage and a brick fence on this type of foundation. I can say that with proper calculations and adherence to construction technology, no problems arise with this foundation.

Although our users have accumulated extensive experience in constructing a pile-grillage with a widening at the base of the pile, it cannot be considered a universal solution suitable for any type of soil and structures.

The choice of design is, first of all, based on data from a geological study of the site. Based on the results obtained, the bearing capacity of the soil, soil composition, groundwater level, the presence of subsidence foundations, etc. are determined. After this, taking into account the weight of the building and the collection of loads that the foundation (in this case, the “heels” of the piles) must redistribute to the ground, the most appropriate and cost-effective type of foundation is selected.

Based on practical experience, we can say that a pile-grillage foundation with an expansion at the base of the pile is most in demand on highly heaving soils, in areas with large differences in elevation. Under these conditions, the use of another type of foundation may not be economically viable due to the large volume of earthen and concrete work.

It should also be remembered that the calculation of a pile-grillage foundation is not as simple as it might seem at first glance. In case of gross violation of technology construction, without knowledge of soil type, groundwater level, etc. such a foundation can turn into a “time bomb” under the house. Moreover, to the final cost of a pile-grillage foundation, it is necessary to add measures for its insulation, installation of a blind area, drainage of surface and groundwater, and installation of an intake.

The fence is installed around the perimeter of the basement and closes the underground space under the house so that the wind does not blow around there.

This approach will allow you to understand whether it is profitable or not to arrange this type of foundation. A pile-grillage foundation is a “ribbon” (grillage) torn from the ground, to which piles are added. Hence (based on calculations) it may turn out that in some cases it is more economically profitable to build a classic shallow insulated strip foundation.

The main features of a pile-grillage foundation, with a widening at the base of the pile, include:

1. The pile is laid below the freezing depth (depending on the region).
2. At the bottom of the pile, a widening is made - “heel” with a certain ratio to the diameter of the pile and the calculated load-bearing capacity. Thus, the pile is reliably “anchored” in the ground.
3. Grillage should not touch or lie on the ground.

The above measures help minimize the forces of frost heaving.

Vzik User FOUMHOUSE

I am installing gates. Due to my professional activity, I often see problems that arise with the support pillars of the entrance group. Due to the influence of frost heaving forces, poles “walk”, gate leaves warp, gates jam, etc. Of course, you can pour a monolithic concrete strip under the entire perimeter of the fence, but this is also not a panacea. I have seen many “torn” ones, and in terms of money this option turns out to be the most expensive.

Based on my knowledge and experience gained during the construction of the house, Vzik I decided that the TISE foundation would also be suitable for the fence. As four years of experience in operating a heavy brick fence showed, the forum member was right. Despite the frosts and winters with little snow, during which the ground freezes deeply, the fence remains level and standing. There were no movements of the foundation, no distortions of the entrance group - swing gates and wickets - during operation. The more interesting is the design and method of erecting this foundation.

To build a fence Vzik started back in 2012, doing it simultaneously with the construction of the garage.

On its site, the soil consists of the following layers:

• “fertility” - about 20-30 cm;
• sand 0.5 m.

The forum member advises not to drill a pile pit manually, but to rent a motorized drill with an auger with a diameter of 25 cm.

Vzik

While I was still drilling holes for the foundation of a house, I realized that doing it manually is a thankless task. Compare: on the first day, two people were able to make one hole “on clay” with a diameter of 25 cm, a depth of 1.8 m and a lower widening of 60 cm. In 10 days, only 30 piles were completely mastered, and 50 were needed! We decided to continue drilling with a motorized drill.

After renting a motorized drill, things started to get more fun. In just 2 hours, 20 preparatory holes with a depth of 1.5 m were drilled. After that, they were deepened to 1.8 m and widened at the bottom with a Tises drill.

Therefore, when it came to making holes for the foundation for the fence, the choice was obvious - to drill everything only with a motor drill. In one day, 50 holes were drilled to a depth of 1.5 meters, after which they were deepened with a hand drill to 2 meters and a lower expansion was made.

Advice: it is better to do the “heels” immediately before pouring the concrete, otherwise they may crumble ahead of time.

When manufacturing this type of foundation, we adhere to the following technology:

1. Because the speed of preparation of extensions drilled manually is low; there is no need to order a mixer with factory-made concrete. The pile is filled with self-mixed concrete. You can do 5 piles per day. This saves money and makes you less tired.
2. For a pile with a diameter of 25 cm, we knit the frame from 4 reinforcing bars with a diameter of 10-12 mm. A welded metal mesh with a cell of 15x15 cm is used as a connecting element. Such a square fits well into the drilled hole. Releases of 2 cm on each side set the direction for the reinforcement frame and provide a protective layer of concrete.
3. The reinforcement frame can be knitted not with knitting wire, but with plastic ties. Although this method is somewhat more expensive than using wire, it saves time and greatly simplifies the process of knitting the frame. The strength of the screeds is sufficient for the reinforcement cage to withstand pouring concrete mixture and further vibration. After the concrete hardens, the screeds no longer bear any force load.

Vzik

At my construction site, I tied all the reinforcement frames (under a house, a fence, etc.) with ties; I didn’t use wire at all. Of course, if you tie with wire, it is a little more reliable, but practice has shown that a plastic tie can cope with the task.

By the way, when using ties instead of wire, we get another bonus that concerns the pouring of piles with widening at the bottom. What is the essence of the idea that the user with the nickname used Destructor, clearly visible in the following photos.

We bend the “legs” (at the bottom of the frame) of each of the four reinforcing bars at an angle of 90 degrees. The curved ends look inside the frame. We knit the frame using plastic ties. Next we proceed as follows:

• Pour some concrete into the heel.
• We lower the frame into the drilled hole.
• We turn the reinforcing bars “legs” bent at an angle with the ends outward.
• As a result, the ends of the “opened” reinforcing bars enter the “heel”, ensuring a reliable connection of the widening with the “body” of the pile after the concrete hardens.

Destructor User FOUMHOUSE

When the “legs” are opened, the reinforcement slides well in the plastic screed. If you tie everything together with wire, it takes more time, and it will be difficult to turn the reinforcing rod.

In order for concrete to be poured into the hole “without a hitch”, we do it this way: we insert a special device into the drilled hole - an adjustable “neck” made from rolled tin and wooden blocks (you can come up with your own version of the device).

Advice: it is better to have several such devices in order to pour several piles at once. You shouldn’t take them off right away, because... the concrete has not yet hardened. Let the “neck” stand for about an hour, but you also don’t need to leave it for a long time, otherwise they will be caught by the concrete, and then you won’t be able to remove the “neck”. After removing the “neck”, you can put a plastic bag on the head of the pile. This is necessary so that the moisture does not evaporate and the normal process of concrete hardening occurs.

A sleeve rolled from roofing felt is inserted into the “neck” and the hole. Then we lower the reinforcement cage and pour the concrete, not forgetting to vibrate it properly, using a vibrator, and not the “bayonet” method. We make the concrete mixture as “hard” as possible, i.e. with the minimum amount of water required to mix it.

Concrete should not be liquid, i.e. spread, as beginners often do, thinking that it’s easier to lay it this way. To improve the workability of the “hard” mixture, we do not hesitate to use plasticizers.

Using a vibrator with a long mace, you can easily vibrate and thoroughly compact even hard concrete.

One more point that needs to be paid attention to. To make piles, it is often recommended to use sewer or asbestos pipes of the required diameter as formwork. According to users of our portal, the most budget-friendly and easiest way to fill a pile is to use a roofing felt “shirt” for this. Moreover, it can be used even if it is necessary to fill high piles that will protrude above the ground by 0.5-1 meter or more.

Oldvist User FOUMHOUSE

I poured the piles in roofing felt. The height above the ground was 50 cm. The diameter of the piles was 20 cm. Ruberoid was wrapped with tape only in two places where the pile protruded above the ground. To make a cylinder from a piece of roofing felt, I wound it around a sewer pipe of suitable diameter. Then he lowered them into the well and took out the pipe. I filled the pile with self-mixed concrete. Everything vibrated properly, nothing broke or came apart.

If you need to fill a pile more than 1 meter above the ground, you can proceed as follows: make two roofing felt “shirts”. First, pour concrete into the first one so that it does not reach the top edge of 10 cm. We insert the second “shirt” inside the first one, adjusting the required level, lowering or raising the roofing material cylinder. Then we pour the concrete further.

BraniganZ User FOUMHOUSE

I poured a pile 1.1 meters high from the ground like this, nothing fell.

An interesting method for making a roofing felt “shirt”, proposed by a forum member with the nickname face_ltd.

A traditional strip foundation performs its tasks perfectly when built on fairly dense and stable soils.

In more difficult conditions, other support structures are required that can create a solid foundation on problematic or completely unstable soils.

The optimal option is piles that are able to rest on deep dense layers, passing through unstable surface layers and practically not forming a structural connection with them.

This solution to the problem allows you to get a stationary and reliable foundation, save money and, often, time.

Let's consider one of the most successful options - type.

A pile-grillage foundation is a system of vertical supports (piles) rigidly connected by a common external load-bearing belt (photo below).

The piles rest on dense layers of soil, and the grillage carries the walls of the house, evenly distributes the load and transfers it to the pile system.

This type of foundation has a lot of structural options, can withstand loads of various types and can be used in the most difficult conditions. Different types and materials of piles can be used; the grillage can be a simple support line or a powerful reinforced concrete strip.

Various combinations of these elements make it possible to create a foundation with the necessary parameters, optimally suited to the existing loads, operating conditions and hydrogeology of the site.

The presence of a grillage is typical for any type of pile foundation, so they can all be classified as part of this broad group.

Existing types

Types of pile foundations are distinguished by the type of piles.

There are:

• Rack piles. They are immersed in the ground until hard contact with dense soil layers appears. They form the strongest supporting structure and are capable of supporting buildings of any weight and number of storeys.
• Hanging piles. The load-bearing capacity of these supports depends on the frictional force on the side walls and on the strength of the soil cushion under the tip, formed during immersion. This design is convenient when dense layers of soil are too deep, but can suddenly change its parameters due to changes in groundwater levels or other processes.

The material for making piles is:

• Wood. The most ancient and traditional material, which has many disadvantages. With the advent of other, more stable and durable types, wooden piles have practically disappeared from the arsenal of builders, although they are still used in some places (in private construction, for the construction of auxiliary buildings).
• Metal. Driven piles are not specially produced; in this role, pieces of rails, channels or I-beams of suitable size are used. Screw piles are manufactured completely ready for use. The specificity of the metal does not allow for durable supports due to corrosion caused by electrochemical processes and the presence of stray currents.
• Reinforced concrete. The most common type of piles. The most durable are driven ones, manufactured using special technology using stressed reinforcement. Bored piles are cast from concrete directly on the site, which is convenient, reduces transportation costs and the overall level of use of construction equipment, but significantly increases the production time due to the need to cure the concrete to gain structural strength.

There are three main types of pile foundations:

• On driven piles. The immersion of trunks is carried out by special machines. The process does not take much time, the supports are strong and reliable. The disadvantage is the impossibility of carrying out work near the buildings in use due to soil movements that occur during immersion.
• On bored piles. This type of piles is convenient because it does not require transportation, unloading, or the use of lifting equipment. A sleeve (a type of formwork made from roofing felt or plastic pipe of suitable diameter) is lowered into a pre-prepared well, a reinforcement frame is installed and concrete is poured. All operations can be performed independently, but a fairly long period of holding the piles will be required for the concrete to harden.
• On screw piles. They are made of steel pipes with a wall thickness of at least 4 mm. The lower part has a welded or cast pointed tip and spiral cutting blades. Driving screw piles resembles the process of screwing a screw - the blades provide immersion, the sharp tip pushes apart or splits the obstacles encountered. Screw piles can be installed manually, if necessary, they are removed and reused in other places. The service life depends only on the intensity of corrosion.

NOTE!

All pile foundations cannot be created on rock or coarse rocks.

Types of grillages depending on location

Depending on the depth of immersion, there are three types of grillage design:

• Recessed. It is a complete analogue of a recessed strip base. It is immersed to a depth below the freezing level in order to eliminate heaving loads directed vertically upward. At the same time, the developed side surface of the wall experiences maximum values ​​of lateral loads, which must be taken into account when designing. It is not used on difficult or waterlogged soils due to the lack of technological conditions for the production of concrete casting.
• Shallow. It is the most common design option for a pile-strip foundation, where the strip is immersed to a small (40-70 cm) depth. This option is much more economical than the buried one, since it does not require such a serious amount of excavation work.
• Non-buried. In this case, the grillage is installed above the ground surface, forming a gap of a certain height. This option is used on soils that do not allow extensive excavation work - waterlogged, excessively loose, prone to heaving or seasonal movements.

Some experts fundamentally distinguish between pile-tape and pile-grillage support structures due to the presence or absence of immersion of the tape into the ground. Others combine them into one group, since the general design of both is practically the same.

Use Cases

There are several options for using grillage material:

• Wood. Either a solid beam 150:200 or 200:200 mm is used, or a pack of edged boards 50:200, assembled in 3 or 4 layers. The resulting beam has high load-bearing capabilities and is easy to process and install. The cost of wood is relatively low, so a grillage of this type is the best option for houses that do not have a lot of weight (wood, aerated concrete, foam concrete).
• Metal. This type of grillage allows you to get a strong base, rigidly connected to the pile heads. The result is a durable structure, the installation time of which is minimal, and the result is very reliable. A channel, I-beam or rail is used as beams; they are attached to the tops of the piles by welding. Most often used in combination with screw piles.
• Reinforced concrete. This type of grillage is built using the conventional technology of casting a monolithic strip (floor tile). The only difference arises from the presence of an air gap between the soil and the bottom of the base. In addition, the reinforcement of the piles must be rigidly connected to the reinforced belt of the tape, forming a monolithic supporting structure. This procedure forms a powerful and rigid base that is resistant to all types of loads. The disadvantage is the long hardening time of concrete, which stops work for a month.

Its required height

The height of the grillage is directly related to the material of the walls of the house. If you plan to build a brick (concrete, cinder block) house, then the minimum height is considered to be 15-20 cm above ground level. For wooden houses, the height of the grillage should be slightly increased and be about 40-60 cm.

This will provide the necessary flexural rigidity and will allow the wood to be separated from sources of moisture below.

This refers to the snow cover, the height of which must also be taken into account. If the region has very snowy winters with high snowdrifts, it is necessary to calculate the height of the grillage to exceed their level.

Laying depth - what it depends on

The depth of placement depends on the condition of the soil on the site.

All related factors are taken into account:

• Groundwater level.
• Availability and volumes of soil water.
• Possibility of flooding in spring.
• The presence of seasonal changes in hydrogeology, an increase or decrease in the degree of filling of all aquifers.

To select the correct depth, it is often necessary to collect information from local geological and meteorological departments, consult with experienced builders, and refer to various SNiP applications.

It must be taken into account that all values ​​​​indicated in various sources are minimum, i.e. It is allowed to increase the lifting height, but it is impossible to reduce the height of the gap.

Device

The grillage is a supporting structure located under all load-bearing walls, both external and internal.

It is assembled into a single strip; the beams are assembled into a single structure using conventional technologies characteristic of this material:

• Wooden beams are connected half-timbered with a jute tape sealing the joint.
• Metal beams are welded to the ends with reinforced connections with threaded elements.
• The concrete grillage is cast in the form of a monolithic element, rigidly connected to the piles by a common armored belt.

Each beam is rigidly connected to all supports located under it. The distance between them must correspond to the magnitude of the load; excess will contribute to the deflection of the beams and the deformation of all adjacent elements. Longitudinal connections of beams can only be located above the pile head; joining them in the span is prohibited.

How to calculate a monolithic base

The calculation of the pile-grillage foundation is carried out experienced and competent specialists.

This is a complex and responsible engineering task that is beyond the power of outsiders and those without special training (the work is carried out using diagrams and formulas).

If there is no opportunity to contact specialists, you can use online calculators, which give a fairly correct answer within a few seconds and completely free of charge.

If for some reason you need to calculate the supporting structure yourself, perform the following steps:

• The weight of the house is calculated along with the property, wind and snow load, and additional elements. This point is the most difficult, since it is necessary to take into account absolutely all the factors influencing the foundation from the side of the building. Some values ​​can be found in the SNiP tables, for example, the magnitude of wind and snow loads characteristic of a given region.
• The resulting value is multiplied by the structural strength coefficient. Usually it is taken equal to 1.1, but in some cases an increased coefficient of 1.2 is used.

The value of the safety margin is relevant only for this configuration of the house.

All additional elements, decoration, furniture or extensions will increase its weight and load the foundation beyond its design value.

Therefore, it is quite acceptable to take a much higher strength coefficient in order to avoid future deformation or destruction of the foundation.

After the load is determined, the number of piles is calculated.

The total weight of the house is divided by the permissible load per unit and the result is rounded to the nearest whole number.

The permissible load on finished supports is indicated in the product passport; for bored piles it is calculated independently, using the methodology specified in SNiP or other sources.

Step-by-step DIY installation instructions

Let's consider the procedure for installing a reinforced concrete grillage located at a height of 30 cm above ground level (one of the most difficult options).

Procedure:

Preparation

The site is cleaned and leveled (if necessary). Remove all foreign objects, plants and other obstacles.

Pegs are used to mark the area. For driven piles, it consists of installing one peg on the axis of the supports; for bored piles, the lines of the outer and inner perimeter are marked. They also require preliminary drilling of wells, which is carried out based on the results of test drilling.

It determines the depth of dense layers of soil and is carried out in any case, as it makes it possible to determine the length of the trunks.

Installation of piles

Piling is driven using special machines.

It is necessary to draw up a driving plan so that the finished piles do not cut off the installation points of the next supports.

Usually installation is carried out in a spiral or snake, sequentially moving from one point to another.

For bored piles, wells are lined (immersing a pipe made of rolled up roofing felt or a piece of plastic pipe of the required diameter). Then an armored belt is assembled and lowered into the well, the dimensions of which must be selected so that it easily fits into the hole.

The length of the reinforcement must exceed the length of the well, so that it can subsequently be rigidly connected to the reinforced belt of the grillage. Then the well is filled with concrete and kept for the required time (28 days).

Construction of formwork

To build formwork, it is not necessary to wait for the concrete to harden in the wells. If driven piles are used, they usually wait about a week for the shaft to “suck” (a construction term for restoring the soil and sealing it tightly to the side walls).

Formwork is a kind of long wooden tray, the internal dimensions of which repeat the shape of the future grillage.

The assembly is made from edged boards, trying to prevent the formation of cracks and gaps.

The height of the formwork should slightly exceed the height of the grillage. To provide rigidity to the lower section, a series of supports are installed on the ground to prevent deflection of the bottom of the formwork. The inner part is covered with polyethylene, which prevents water or material from escaping from the formwork.

Creation of an armored belt

The reinforcement frame is created using conventional technology- working rods with the help of smooth auxiliary reinforcement are installed in the desired position according to the design diagram and general rules.

An important point is the rigid connection of the pile reinforcement and the reinforced belt of the tape, for which it is best to use welding. The remaining elements are connected by knitting with soft wire.

Pouring concrete

Concrete is poured after the concrete has completely hardened in the piles.

This is important, since the weight of the reinforced concrete grillage is very large and can deform uncured concrete.

The pouring must be done as quickly as possible, without interruptions, in order to obtain an absolutely monolithic support with a high degree of rigidity. The concrete is leveled and covered with burlap or polyethylene, and periodically watered with water for the first 10 days.

After 10 days the formwork is removed, after which the tape is kept until it hardens completely, which occurs 28 days after pouring.

Floors on the ground

Floors on the ground are used to create a grillage structure immersed in the ground. If there is an air gap, creating a ground floor becomes too difficult, ineffective and impractical.

The inner part of the tape is covered with a layer of sand cushion. Then a layer of geotextile is laid on it and crushed stone is poured, onto which a layer of crushed stone is poured through an additional layer of geotextile.

The entire backfill is compacted sequentially, achieving the best possible result. Then a layer of screed is poured on which the heat insulator is laid.

A screed is again poured on top of it, inside which a heated floor system is installed.

This screed can be covered with a finishing coating.. The floor cake is quite multi-layered, but it provides high-quality heating and prevents heat loss due to contact with the ground.

Waterproofing technology

The grillage is waterproofed using one of the most common materials:

• Hot bitumen.
• Bitumen mastic.
• Pasting with roofing felt.
• Application of impregnating compounds.

The simplest and fastest option is to use bitumen mastic, which performs its tasks perfectly and is sold in ready-to-use form. Apply by roller or brush, usually in one or two coats.

Insulation scheme

Waterproof materials are used for insulation:

• Liquid polyurethane foam.
• Extruded polystyrene foam (penoplex).
• Styrofoam.
• Expanded clay.
• Foam glass, etc.

The most convenient and effective option is considered to be penoplex, which is glued in a dense layer to the entire surface of the grillage, both internal and external.

Somewhat worse but it is much cheaper to use polystyrene foam, which is also resistant to moisture and is an excellent heat insulator, but has the ability to crumble and is excessively brittle.

Useful video

In this section you can see how to make a pile-grillage base (reinforced foundation) with your own hands, as well as how the grillage is reinforced:

Conclusion

Pile-grillage foundations are one of the most successful and reliable types of foundation.

They are able to perform their functions in the most difficult conditions, respond well to changes, and allow construction on the most problematic soils.

In most cases, the construction of such foundations is cheaper than the construction of a traditional belt.

These advantages make pile-grillage foundations preferable among most users whose plots are located in lowlands, in flooded areas.

The possibility of self-construction only increases the appreciation of this technology among builders, allowing the work to be completed at a convenient time and fully comply with the technology.

In contact with

When it comes to a columnar or pile foundation, two functionally significant elements are described - piles and grillage. Piles are designed to accept and transmit loads to the ground, but the question of what a grillage is is of interest to most private developers.

Description of the grillage

A grillage is a horizontally located part of a pile or columnar foundation. The main purpose of this element is to evenly distribute the load from the entire building onto the piles by combining them into a single structure.

The grillage can be located at different levels relative to the surface of the ground, various materials are used for their manufacture, and their design may be different. Depending on this, the grillage is distinguished according to the following characteristics:

• Location.
• Material of manufacture.
• Execution type.

Types of grillage by location

Depending on the location relative to the ground level, the following types of grillage are distinguished:

• High. This type is located above the ground at a distance of 25 cm and above. This allows you to create additional floor ventilation and prevent the appearance of mold and dampness. In addition, the elevation above the ground makes it possible to inspect the condition of the foundation and repair it in a timely manner. Also, the space under the floor can be used as an additional area for storing garden tools and other tools. The disadvantage of such a grillage is the inability to arrange a basement.
• Short. A grillage of this type is located flush with the ground surface. To construct it, a small layer of soil is removed to create a kind of air cushion. As a result, there is no contact between the grillage and the soil. The advantage of this type is the absence of space through which an indefinite amount of heat can escape. The disadvantage is that it is necessary to create insulation for the air cushion, otherwise the soil will crumble into the open space.
• Recessed. With this type of grillage, the room is comfortable due to heat retention, reliability and durability. The manufacturing process involves preparing a trench, installing piles, installing formwork and pouring concrete into the finished structure.

Types of grillage depending on the type of execution

Depending on the design, the grillage can be of two types:

• Monolithic.
• Made.

In the first case, the grillage is made in the form of a solid slab or a closed beam. The main application is the construction of low-rise buildings. The second type involves assembling a structure from individual elements equipped with special fasteners. The process of manufacturing a prefabricated grillage is considered labor-intensive and costly, so it is used in the construction of multi-story buildings and industrial buildings.

Material for making grillage

A grillage can be made from the following materials:

• Tree. A wooden grillage is excellent for constructing houses made of timber and logs. The design is characterized by high strength characteristics, environmental friendliness and safety. However, the tree requires special attention and additional protection. In particular, the wooden grillage should be treated with a waterproofing compound, fire retardant and antiseptic solution.
• Reinforced concrete. Steel reinforcement in combination with high-quality concrete allows you to obtain a strong, reliable and durable structure that is resistant to wear. Thanks to this, the entire structure will serve flawlessly for many years. You can read our previous articles.
• Metal. A grillage made from I-beams or channels is durable and reliable, but it has one drawback - the need to use construction equipment to lift heavy loads.
• Concrete. Such a grillage has a significant drawback - when the structure is bent, cracks may appear, which in turn cause the destruction of the grillage. And in this case it may be necessary. However, when constructing low-rise buildings and in the presence of a large number of supports, such a grillage may well be used.

Construction of a foundation from bored piles with a grillage

The foundation on bored piles with a grillage can be called one of the strongest and most durable. However, this result can only be achieved if all calculations are made correctly and construction technology is followed.

The number of supports is calculated taking into account all the necessary factors and parameters, including the design of the house.

Preparatory work and site marking

Before starting construction of any foundation, the site should be prepared for work. To do this, it is necessary to remove large debris, excess vegetation, stumps and tree roots. For more convenient work, the area can be leveled.

Then markings are made on the prepared site. First, mark the places where the corners of the house will be located, and drive in wooden pegs or metal fittings. To determine the contour of the future foundation, a construction cord is pulled between the stakes.

Excavation

Drilling holes for arranging bored supports is carried out using a regular garden auger. The depth of each well is determined depending on the level of soil freezing. In most cases, experts recommend lowering the piles to a depth of 1.5-2 meters, this allows you to pass the level of freezing and the location of groundwater. complicates the process a little, since it requires adding sand to each hole in a layer of 5 cm.

Installation of formwork and reinforcement

Asbestos-cement pipes are also used as supports for a bored foundation. In some cases, it is possible to install cardboard products, but they must be impregnated with bitumen mastic or waste machine oil. The pipes are lowered into prepared wells, and the elevation of the upper edge of each support above the ground surface should be at least 5 centimeters. If the soil on the site is prone to seasonal heaving, then the distance from the ground to the upper edge of the pipe is increased to 10 cm. In any case, the foundation grillage on bored piles should not lie on the ground or touch it.

To increase the strength of future supports, it is necessary to install a frame of metal rods in each pipe. To tie together the reinforcement, special clamps are used, which are located in increments of 1 meter. The length of the reinforcement cage depends on the depth of the well, the main thing is that the rods rise 15 centimeters above the level of the pipe.

Pouring concrete into formwork

To fill bored supports, it is recommended to use a mixture of high grade cement, coarse sand and the required amount of water. The components are taken in a ratio of 1:3. The prepared mixture is poured into the pipe in small portions, periodically piercing the solution with a metal rod. This allows you to remove voids from the concrete mixture that are formed during the pouring process. The pipes must be filled with concrete to the very top. Previously we wrote about
.

Grillage arrangement

For a foundation on bored supports, a grillage in the form of a monolithic concrete strip is required. To make it, you can build a formwork with a bottom, but here you can simplify the process a little. Due to the fact that the grillage will be located at a short distance from the ground surface, it is possible to install the side parts of the formwork, placing them at a distance in accordance with the width of the grillage.

A concrete base about 5 cm high is poured on top of the roofing material, and after it sets, the formation of a frame from reinforcement rods begins. At this stage, it is important to connect the grillage frame with the rods of the bored supports.

During the process of pouring the grillage tape, it is also necessary to pierce the solution with a shovel or metal rod.

Is a grillage always needed?

For the strength and reliability of a pile or columnar foundation, it is necessary to connect separate supports into a single structure. In most cases, a grillage is used for this purpose, however, in some situations this element may be missing:

• With or timber, the grillage function is assigned to the lower crown of the main frame of the house.
• When constructing frame buildings, the bottom frame is used as a grillage.

The situations listed above apply to low-rise construction and the construction of small private houses. If the building has more than two floors and a massive structure, then care must be taken to provide additional rigidity to the base.

A grillage is a necessary element of any columnar or pile foundation. Its presence allows you to evenly distribute the load of the structure between separate supports and obtain a strong, reliable and durable structure.