There are a large number of foundations. The choice of one option or another depends primarily on the characteristics of the soil and the size of the building under which it is being built. A strip foundation on piles combines the advantages of two foundations: strip and pile. We will consider the features of its construction below.

Advantages and disadvantages of strip foundations with piles

This type of foundation is relevant when the soil has high humidity. If, after rain falls, water continues to remain in the upper part of the soil for several days, then exclusively a pile-strip type of foundation is used to equip the building. Using the tape in connection with the piles allows you to evenly distribute the load from the building. Piles, in turn, are so-called anchors that stabilize the building in the process of excessive soil moisture.

A pile-strip foundation involves a combination of two foundation options: pile and strip. The pile foundation is constructed by installing screw piles into specially prepared recesses. And in order to give the structure greater rigidity, it is strengthened by installing a shallow strip foundation.

The combination of two technologies allows you to achieve the following advantages:

• possibility of use on almost any type of soil, even with a large slope;
• construction both on weak soil and on soil with increased hardness;
• accessibility and simplicity of materials used in the work process;
• resistance to soil movement and heaving;
• affordable cost of construction in a relatively short period of time;
• the possibility of self-production, without the use of special equipment.

However, the construction of this type of foundation involves carrying out detailed calculation operations to determine the depth of the pile, laying a strip foundation, the number and location of piles, etc. In addition, it is not recommended to install too large piles on this foundation option. This foundation option does not imply the arrangement of a basement underneath.

The main difference between a pile-strip foundation and a conventional strip foundation is that the building rests only on a sand cushion, but also on piles, thereby reducing the overall load on the soil and preventing its uneven subsidence. The piles thereby transfer the load to harder soil, which is located deeper than the strip foundation laid. The type, size and cross-section of piles are selected individually and depend on the geological features of the area.

The difference between a pile foundation and a strip foundation on piles is that the strip, the so-called grillage, allows you to build a brick house or a building made of stone and blocks on piles. At the same time, the load from it will be distributed evenly. The tape that is installed on this type of foundation is installed in a shallow, recessed or non-recessed position.

The most common option is a shallow tape. The depth of the tape is from twenty to forty centimeters. In this case, bored piles are used, with a circular cross-section and additional reinforcement. The tape, in this case, rests on a cushion made of sand and gravel, the height of which is about twenty centimeters.

Please note that this foundation option is used if the soil on the site is characterized by high or low heaving. The tape is located in weight, that is, above the zero mark, if the soil is particularly heaving.

Calculation of strip foundations on piles: features of implementation

Before starting the manufacture of a pile-strip foundation, a series of operations should be carried out aimed at determining the width of the strip, the diameter of the piles and the depth of their laying. In addition, you should calculate the number of piles that will evenly distribute the load.

It is preferable if this work is carried out by specialists who have previously dealt with detailed calculations. Since the duration of operation of the entire building directly depends on the correct calculation of these characteristics, it is not recommended to save at this stage.

In the process of calculating a strip foundation on piles, the load that will be placed on it should be taken into account. In addition, the soil should be examined for moisture content, clay and other inclusions.

When making calculations, you should take into account such characteristics as:

materials from which the structure will be constructed;

number of floors and dimensions of the building;

the type of soil on the site and its geological features.

Technology for constructing strip foundations with bored piles

This foundation option is based on the use of bored piles, the bearing capacity of which is more than 1.5 tons. Therefore, for an average-sized building, 40-50 such piles are enough. The installation of such a foundation is done quite quickly and does not require any special costs.

The piles are laid in such a way that their lower part is located lower than the freezing level of the soil. In order to provide additional protection for the piles from moisture and freezing, they are covered with roofing felt. Ruberoid is also capable of reducing soil pressure on piles in severe frost.

Foundations on bored piles are most often constructed using two technologies:

• use of a strip base mounted on piles;
• production of a suspended grillage.

The second option is relevant for soil with very high heaving. The first option involves deepening the monolithic grillage twenty centimeters into the ground.

The installation of a strip foundation on piles involves the following stages of work:

1. Performing calculations for the foundation.

We recommend entrusting this stage to specialists, since in order to carry out calculations yourself, you should re-read a lot of literature related to the soil and its characteristics. In addition, it is necessary to examine the soil for its moisture content. Based on the results obtained, the width of the foundation tape, the depth of piles, the type of piles, and the material from which they will be made are determined.

2. Marking the base for the foundation.

This stage involves preparing the site: clearing it of vegetation, leveling it as much as possible. Next, using a rope and pegs, markings are made for the foundation, and the installation location for bored piles is determined.

3. Drilling wells for piles.

After determining the installation location for each pile, it is necessary to arrange holes for them. The main condition for determining the installation depth of each pile is its placement below the soil freezing depth. You can learn about the depth of soil freezing from its studies or from a special map that indicates this indicator for a certain area.

4. Preparation of wells for installation of piles.

Roofing material must be placed inside the previously prepared well, which is carefully fixed in it. In this case, it is advisable to install roofing felt in two layers. If the condition of the well in the future is quite stable, then there is no need to install a casing pipe. However, if the soil on the site is quite swampy or contains a lot of clay, care should be taken to install casing pipes, which will give the piles greater rigidity. Sand is used to fill the free space between the pipe and the base of the well.

5. Installation of steel frame.

A frame made of steel reinforcement must be lowered into the inside of the pipe or well. Please note that it should not rest against the bottom of the well under any circumstances.

6. Filling wells.

At the next stage, the previously prepared base is filled with high-quality concrete mortar. You should not skimp on foundation mortar, since the durability of the entire house directly depends on its strength. It is preferable to use industrial concrete; if this is not possible, then you should make it yourself using a concrete mixer. Perform the pouring of each pile separately, without allowing interruptions in the process of pouring one pile. To remove air from the concrete and ensure compaction, use a concrete vibrator. Thus, the structure will acquire additional rigidity.

The upper part of the well is not poured, since part of the reinforcement cage must subsequently be connected to the concrete strip. After the concrete solution has hardened, a sand base should be arranged on the surface of the future strip foundation.

7. Making tape.

Next, you need to assemble the formwork. For its manufacture, an edged board is used. A previously prepared reinforcement frame is installed inside the formwork, which is filled with the same concrete solution as the piles. Please note that the use of reinforcement is mandatory, as it increases the resistance of the foundation to high loads and makes it more flexible. In addition, reinforcement is used to connect the grillage to the piles. Next, you should wait at least three weeks until the concrete has completely set, and only then continue work.

Shallow strip foundation on screw-type piles

If we consider which is better - screw piles or strip foundations, then you should familiarize yourself with the advantages of each type of foundation. An excellent combination of the two above options is a strip foundation on screw piles.

Screw piles differ from bored piles in their design. The lower part of the bored pile has blades, with the help of which it is easily screwed into the soil. For the manufacture of supports, steel is used, most often of the cast type. It is possible to weld finished elements together; however, such piles are less durable than cast ones. Pile foundations are characterized by high bearing capacity, so they are quite popular. Adding a ribbon to this option foundation, increases its rigidity and strength.

If the soil is of the clayey, loamy, peat, or swampy type, then a strip foundation with bored piles must be installed on it.

Among the advantages of a strip foundation on piles, we note:

• affordable cost, the piles do not need to be filled with concrete and additional costs for their production;
• the piles are quite easy to transport;
• one day is enough to install screw-type piles, so the process of making the foundation does not take much time;
• the duration of operation of a structure installed on such piles is quite high;
• possibility of installation on soil with high moisture content and heaving;
• the service life of steel supports is at least one and a half centuries;
• there is no need for preliminary preparation of the trench for the piles; they are installed directly into the ground;
• work is carried out both in winter and in summer;
• if the site is uneven, then with the help of piles it is possible to get rid of this disadvantage, without first leveling the site.

However, installation of screw piles on rocky terrain is particularly difficult. Since during the installation process there is a risk of blade breakage. Thus, the bearing capacity of such a foundation is significantly reduced. The foundation on screw piles does not allow building a basement or ground floor under the house. In addition, the sewer system and water supply system require additional insulation. In order to protect the surface of the pile joint from corrosion, they need additional treatment using bitumen mastic.

Additional installation of a strip foundation on a base with screw piles implies the following advantages:

• the possibility of independently constructing a foundation strip;
• ease of work;
• giving the screw structure additional rigidity;
• uniform load transfer to screw piles;
• stability and tendency to deformation of a building built on this type of foundation;
• resistance to groundwater;
• high strength and long service life.

However, arranging a strip foundation involves performing complex operations such as preparing concrete mortar, making reinforcement, installing formwork, pouring, etc. Also, after its manufacture, you should wait about a month so that the concrete gains additional strength.

Therefore, if a building made of stone, brick or blocks is being built on soil with high heaving, then the combination of a strip and pile foundation is an excellent option that will make the foundation a stationary, strong and stable foundation for any structure.

Strip foundation on piles video:

For unstable soils, it is better not to use classic foundations in the form of a strip of reinforced concrete. In order for a house to stand on such a support stably, the technology will have to deepen it too much. And this means an increase in the volume of excavation work and spending on concrete. It would be much more rational to perform a combined pile-strip foundation with your own hands, which absorbed the best aspects of both piles and strip construction.

What is a strip foundation on piles?

In terms of structure, a pile-strip foundation is a structure made of piles dug into the ground to a depth below the freezing point, and a reinforced concrete grillage on them. It combines the advantages of two types of foundation structures. The grillage tape serves to evenly redistribute loads. And the buried pile foundation plays the role of anchors, which prevent the reinforced concrete from above from “floating away” during soil heaving and strong uplift groundwater.

Scheme: 1-reinforced frame, 2-asbestos-cement piles, 3-concrete strip, 4-technical terminals, 5-waterproofing, 6-ventilation holes

A conventional pile-screw foundation is somewhat inferior to the type of supports for houses under consideration in terms of distribution of vertical loads. A reinforced concrete tape laid on piles is more resistant to spot raising or lowering of one of the support pillars. On the other hand, this design outperforms its purely strip counterpart in terms of construction costs, as well as stability on heaving and waterlogged soils.

Types and subtypes of foundation

A strip foundation on piles is ideal in the presence of soils with weak heaving. In such areas it can be used for the construction two-story cottages made of brick. But in general, such a design is more intended for light frame or timber buildings.

However, if the site for the house has a slope, then it will be difficult to do without a pile strip foundation. It will be too expensive to pour a monolithic slab here, and other options will not be able to withstand all the loads that arise in the future.

Based on the depth of immersion of the grillage into the soil, pile foundations with it are divided into two types:

Shallow.

Not buried.

Non-recessed option

In the first case, the tape is immersed in the soil by 20–50 cm, and in the second, it hangs above the ground. Due to its greater strength, heavier buildings can be erected on a foundation with a shallow grillage. However, if the soil is heavily heaving, then the strip part of the structure on piles will simply be destroyed by heaving. It is not made too high, so it is simply not able to withstand strong loads from rising soil.

Advantages and disadvantages

Among the advantages of a pile-strip foundation are:

Sufficiently high installation speed;

Possibility to erect buildings on construction sites with a slope;

A simple technology that makes it easy to build such a foundation with your own hands;

High resistance to movement of heaving soils;

No need to use special equipment.

If the grillage is not buried, then it is not afraid of heaving and moisture in the soil. In terms of service life, this option outperforms its buried counterpart on piles and its shallow-depth strip foundation. It also beats them in terms of cost and the complexity of the work. You will have to dig several times less, the depth of immersion is the same, but you only need to remove the soil under the support pillars. Plus, all construction materials can be delivered to the site without the use of heavy cargo and lifting equipment.

When independently constructing pile-grillage foundations, bored supports made of asbestos pipes are usually used, which are reinforced and filled with concrete inside. It is this option that is considered in the following step by step instructions. In terms of speed of construction, only a foundation made of FBS or screw piles made of steel can compete with such a foundation for a house.

There are only three disadvantages:

The need for additional floor insulation in the cottage;

Inability to use for arranging a basement or basement;

Building weight restrictions.

All types of pile foundations have one common problem - drafts in the underground. In the far north, piles help avoid heating the permafrost layer. At the same time, in other regions, wind freely flowing under a building is a serious problem.

Step-by-step instructions for building a foundation

When preparing to make a pile-strip foundation, you must either plan in advance for high heating costs, or immediately include insulation of the basement-foundation part of the building in the estimate and project. In the second case, you will need moisture-resistant insulation for the walls and cladding, but the home will definitely be warm.

It will be necessary to construct a false wall around the perimeter of the cottage to cover the pile pillars and prevent drafts between them. To do this, you can take facade panels for exterior finishing or corrugated sheets. If you want something more beautiful and elegant, then there are clinker tiles and decorative bricks. There are many finishing materials for the exterior of a building.

The entire process of constructing a belt on piles can be divided into two stages. First, the pile part is made from bored pipes. And then a strip structure is laid on them. You just need to remember to tie them together with reinforcement before pouring the concrete.

In general, the step-by-step instructions for a strip foundation on concrete piles are divided into five steps:

Preparatory and drawing work

Excavation of earth, installation of asbestos cement pipes and their reinforcement.

Pouring permanent asbestos-cement formwork with concrete.

Creation of strip formwork from boards and bars.

Reinforcing the tape on piles and filling it with concrete mortar.

Waterproofing reinforced concrete.

We draw on paper or in the program the future foundation - tape and piles

Marking wells with “stakes” for the piles of the future foundation

Piles must be immersed to a depth below the freezing level of the soil at the construction site. Holes for them will have to be dug 40–50 cm below this mark. The foundation must rest on a stable soil foundation.

After preparing wells with dimensions 10–15 cm wider than the outer diameter of asbestos-cement pipes, a sand cushion is poured at their bottom 30 cm thick. The pipe formwork is installed precisely on this compacted sand. The diameter of the pipes themselves is selected at the rate of 1/3 of the width of the reinforced concrete grillage.

Next, each pile is reinforced with three or four vertical steel rods with a cross-section of 10–12 mm and a length equal to the sum of the heights of the support and the tape on it. They are placed in the pipe at approximately equal distances from each other and from the asbestos-cement walls. To simplify, they can be tied with wire into the desired structure on the ground before installation.

The next stage is pouring the pipes with concrete solution. This is usually done before reinforcing the foundation strip on the piles. But the instructions given may be slightly modified. Then, first, the reinforcement is laid in the grillage and formwork is made for it, and then the whole thing is poured with concrete. The cells of the reinforcing belt are knitted with a size of 30–40 cm, depending on the width and height of the tape.

We fill the piles to the level of the tape reinforcement. The photo shows a situation where the pile was “overfilled” and had to be drilled out to install the strip frame

We dig up the “tape”, add sand, lay down roofing material and knit tape reinforcement

To perform waterproofing, it is enough to take ordinary roofing material and wrap it around the grillage. This is the cheapest option. You can also use bitumen or polymer mastic. On this, the foundation of the house in the form of a strip on stilts is made. In the future, it will only need to be covered with cladding and, if necessary, insulated.

Done - you can lay out the walls

Where to use?

When comparing the pros and cons of using a pile-strip foundation, first of all you need to focus on the material of the cottage walls and the characteristics of the soil. If a dwelling is being built from lightweight building materials and on water-logged soils, then the support discussed above with a grillage raised above the ground is an ideal option. Such a foundation will last for many years and will definitely not be damaged by heaving, and it is not difficult to make. Fortunately, the step-by-step instructions provided allow you to avoid unnecessary mistakes.

At the base of a house being built on a site with weak soil, it is advisable to make a pile-strip foundation with your own hands. The choice of this option is due to the negative impact on the concrete strip, the presence of clay, peat, humus, and groundwater on the site in the upper layer of the earth, creating quicksand.

Under a concrete structure in the form of a tape (grillage), three types of piles are used: ready-made concrete piles, screw piles and bored piles.

Soil category, impact on concrete base

In summer, weak soil in some places under the foundation is washed away, subsidence occurs, and then the foundation is destroyed. With the arrival of cold weather, wet soil freezes and swells, creating pressure on the foundation, which also leads to its destruction.

The problem is solved with the help of piles buried below the freezing line of the soil, resting on a solid layer of earth.

The shallow strip foundation is cast on piles and does not depend on the changing state of the top layer of soil. The number and dimensions of piles and tape dimensions depend on the load and location of the building under construction.

Piles under the tape are made in the bored version, forming a single monolithic structure. The choice of foundation for a house depends on the soil category. For heaving soil, it is advisable to use a pile-tape foundation.

Technology of concrete foundation on stilts for a house

The foundation for a house on stilts can be done on your own, knowing how to make a pile-strip foundation with your own hands in order to avoid mistakes when working independently.

It is important to study the technology and step-by-step instructions for making a foundation. Familiarize yourself with previously built similar structures and ask the contractors about possible problems during the construction of the foundation. Study all the components required for construction.

Construction of a strip foundation with piles

The production of a strip pile foundation can be carried out without the use of expensive equipment by renting the necessary equipment.

The concrete foundation, depending on the purpose of the building being constructed, provides for insulation of piles and tape or is limited to waterproofing. The technological process is reflected in the executive design and, taking into account the preparatory work, includes operations performed sequentially. In the step-by-step instructions for making a pile-strip foundation with your own hands, these operations are reflected:

A house for permanent residence must have a warm foundation, since heat loss will be 30%. Following the instructions will allow you to complete the work efficiently in a short time.

Do-it-yourself foundation for a house

To make a pile-strip foundation with your own hands, it is advisable to have practical experience or work together with a professional.

Before starting work, it is necessary to provide the construction site with electricity and water (there is no centralized - local).

Prepare hand and measuring tools, rent the necessary equipment. Bring materials and components to the site:

• formwork for piles made of asbestos-cement pipes;
• sand and gravel mixture;
• cement;
• reinforcement d = 12 mm and d = 6 mm;
• edged lumber t = 50 mm;
• permanent formwork made of cement bonded particle board with components t = 35 mm;
• insulation made of polystyrene foam boards t = 50 mm;
• expanded clay insulation;
• roofing felt;
• built-up waterproofing;
• hardware.

M400 cement is suitable for making concrete mix

Constructing a pile-strip foundation with your own hands will save money, but will require conscientious study and consistent execution of all technological operations.

Work begins with cleaning the site, removing the vegetation layer, and leveling the site for your home.

They are also planning a ditch to drain groundwater and rainwater from the base of the house.

In addition, a trench is laid out for the tape, its depth is determined taking into account the bearing capacity of the soil.

Before starting work, it is necessary to study the top layer of soil on the site, determine the level of soil freezing and the presence of groundwater. Make an accurate calculation of the size and number of piles for the foundation.

Construction of wells and tapes

We dig and plan the bottom of the trench, controlling the horizontality using a level. On the compacted bottom of the trench we mark and drill holes for the piles. The depth of the well should exceed the depth of soil freezing and penetrate into dense soil by 0.5 - 0.6 m.

We insert formwork into the drilled holes, which should be made of asbestos-cement pipes protruding 0.3 m above the bottom of the trench. At the bottom of the trench, pressing it to the outside, we lay a drainage pipe around the perimeter and lead it into a ditch to drain water.

The pipe is pulled out of the well by 15 cm so that a cushion is formed when pouring

We fill the bottom of the wells and trenches with a drainage layer of sand and gravel, level it and compact it, spilling it with water.

We pull the pipes out of the wells by 0.15 m, so that when concrete is poured, the gravel under the pipes is saturated with the solution, and a cushion is formed to support and hold the piles.

We line the bottom of the trench with a layer of roofing material so that when pouring the concrete does not mix with the drainage layer.

We cut out the roofing material above the holes, leaving open holes for filling with concrete.

Installation of formwork structure

Having prepared the wells and trench for the pile strip foundation, we proceed to the installation of reinforcing frames for the piles and strip. We install connected frames of reinforcement into the wells, which should protrude from the bottom of the trench to the height of the reinforcing frame of the tape.

Along the axis of the walls of the house, we install a reinforcing frame made of mesh on the roofing felt and drainage layer in the trench. The grids are connected to the protruding pile frames and create a single structure.

On both sides of the reinforcing frame we install permanent formwork made of moisture-resistant cement particle board. Inside the outer wall of the formwork we install insulation from polystyrene foam boards. The sides of the formwork are connected to each other by special connections, which determine the width of the foundation strip and hold the formwork walls and insulation in the structure. For more information about pouring the foundation, watch this video:

After assembling the formwork, the entire structure is reinforced on both sides with stops made of edged boards. We use a level to check the exposed formwork for the verticality of the walls and the horizontality of the top edge.

The foundation strip, like the foundation for a house, rests only on piles and is not supported by soil, so it is important that the structure be monolithic. We fill the formwork with concrete grade M300 in one step. First, we fill the wells with concrete, then fill in the tape.

Using a deep vibrator, we compact the concrete in the wells and remove air bubbles. After the concrete mixture has hardened, we dismantle the formwork reinforcement and apply built-up waterproofing to the upper part of the foundation. For a house, a pile-strip foundation is insulated, for which the ground under the building is covered with a layer of expanded clay 0.2 m thick.

A well-insulated foundation will reduce home heating costs by 30%.

Self-construction of a strip foundation on piles will save money and build a reliable, durable foundation for your home.

DIY pile-strip foundation: step-by-step instructions

At the base of a house being built on a site with weak soil, it is advisable to make a pile-strip foundation with your own hands.

Pile-strip foundation belongs to the category of load-bearing structures designed to absorb and transfer all overlying loads to the foundation soil. It consists of a shallow part - a reinforced concrete grillage, and piles that ensure the stability and strength of the entire support system. This type of foundation is characterized by increased suitability for installation in unfavorable geological conditions, and accessibility to independent construction.

Scope of application of pile-strip foundation

The determination of one or another type of foundation is carried out on the basis of engineering geological surveys, the magnitude of the load and the ability of the soil to absorb it. As a rule, the installation of a pile-strip foundation is provided for:

• heterogeneity and multilayered foundation soils;
• multi-storey housing construction using brick and reinforced concrete structures;
• large differences in terrain;
• the presence of moving heaving soils;
• close proximity to groundwater.

But under any conditions, the immersion mark of the pile must be below the seasonal depth of soil freezing.

Calculation of pile-strip foundation

After the construction site has been studied, there is data on the types, thickness and bearing capacity of soils, their moisture content, porosity coefficient, density, the elastic modulus and other indicators of the layers are determined. The main goal of such actions is to determine the grade of concrete in terms of strength, water resistance, frost resistance, calculate the pitch and dimensions of the piles, the dimensions and method of reinforcing the grillage (tape part).

The calculation begins with , acting on the foundation. They are divided into:

• constant: total weight from all overlying structures;
• useful: the weight of people, pieces of furniture, various types of equipment.

To ensure a safety margin for the foundation, the resulting value is multiplied by a factor of 1.3. Next, using specialized programs and established calculation methods, the main calculation of the structure and method of arrangement of the entire structure is carried out. The principle of its implementation boils down to determining the area of ​​the supporting part of the foundation, the load per 1 m2 and comparison with the results of geological soil surveys. To ensure reliability, sufficient strength and durability of the supporting structure, the determination of the required parameters of the foundation elements should be entrusted to a specialist.
Once the design layout has been completed, you can begin preparatory work, and then proceed to the independent installation of piles and grillage.

Preparatory stage

The preparatory work stage comes down to cleaning and leveling the construction site, applying markings using a thread stretched over wooden or metal elements. As a result, the outline of the strip part of the foundation must be placed on the ground, and a recess equal to the depth of its foundation must be selected. The width of the grillage depends on the size and material of the wall itself. For example, for a foam block the width of the tape will be 300 mm, and for brick wall 400-600mm is already needed. As a rule, the depth of the grillage is within 400 mm.

When the main contour is determined, they begin to apply pile markings. The installation locations of the piles are, first of all, the characteristic points of intersection of the walls, and then in accordance with the step determined on the basis of the calculation. In this case, the diameter of the piles should be greater than a third of the width of the grillage.

Pile devices

The technology for constructing piles depends on their type. These can be screw or bored structures. In the first case, the process is not complicated and consists of screwing a metal trunk into the ground. Immersion is carried out manually with the installation of a reference well or mechanized using attachments on a mini-excavator. The use of bored piles is a more labor-intensive process, and therefore will be considered in more detail.
The sequence of installation of a pile-strip foundation is as follows:

• Wells are drilled along the pile markings, for which a hand drill is used; the depth of the well is made taking into account an additional 300 mm sand cushion under the base of the pile; sand must be compacted and well moistened;
• * in order to avoid the collapse of the borehole walls and maintain the homogeneity of the pile body, concreting is carried out after installing asbestos-cement pipes or elements rolled from roofing felt;

• to increase the reliability and load-bearing capacity of the pile, a concrete heel is placed at its base, for which the pipe is filled with concrete by 300-400 mm and raised upward by 200-300 mm, as a result the concrete spreads and the lower part of the pile acquires large dimensions;
• reinforcing cages are installed into the pipe cavity in such a way that the top of the reinforcing bars protrudes for future adhesion to the grillage structure;
• a well-compacted and moistened sand cushion with a thickness of 100-150mm is placed along the bottom of the prepared excavation;
• install formwork for the foundation strip; formwork is an enclosing structure designed to form the required configurations of concrete structures, made of boards, wooden panels, chipboard, laminated plywood;

• start reinforcing the grillage; can be produced either by separate frames connected to each other by working reinforcement, or by forming a spatial structure from individual reinforcing bars; to ensure teamwork between the piles and the strip part, their reinforcement is connected to each other;

• and grillage; ideal if the work is done as quickly as possible in one grip; for denser styling, submersible vibrators are used; in this way the final strength and operational reliability of the supporting structure will be ensured; in natural conditions concrete mixture reaches 70% strength in seven days, after which the formwork can be removed and the construction of walls can begin; and only after 28 days will the concrete gain 100% of its brand strength.

Updated: February 26, 2018 by: zoomfund

A strip foundation buried in accordance with all the rules requires: removal of soil, construction of massive formwork, welding of reinforcement, preparation and pouring of concrete. To carry out the work you will need a large amount of materials, equipment and qualified specialists. You can build a pile-strip foundation for a private cottage on a personal plot or summer cottage on your own, which will reduce costs on all counts. The technology was invented in Finland for frame houses, and it completely justified itself on swampy frozen ground.

Distributing the loads from the above-ground part of the building onto supports with a reinforced grillage reduces the volume of concrete for pouring the buried foundation. The cost of a strip foundation will be 30% more. In addition to saving resources, the combined scheme eliminates the need to dig a deep trench and use complex technology. Monolithic reinforced concrete strip on piles - a stable foundation for buildings made of light materials:

• wood;
• ceramic blocks;
• aerated concrete;
• foam blocks;
• sandwich panels made of chipboard with filler.

The house can be made of logs, solid or laminated timber, cellular or hollow stone. The panels cover a wooden or galvanized frame. Light buildings cannot withstand frost heaving of the soil, so they are installed on a pile-strip foundation, which rests on fixed rocks. This type is also used when there are significant differences in relief.

Prefabricated foundation laying technology

The scheme of a pile foundation with a suspended grillage has found application in conditions of unstable soil, swampy areas and flooded areas. According to the instructions, the monolithic base is poured into the formwork 25–30 cm above the zero mark. This gap prevents the structure from skewing due to winter soil uplift. If the supports are buried below the freezing mark, then the load from swelling acts on them tangentially. when suspended, it is not subject to deformation. An insulated blind area and proper intake prevent storm water from getting under the building.

The structure of the soil and the presence of aquifers are natural factors on which the depth of the foundation depends. Weak types include:

• fine sand (indistinguishable grain fractions);
• sandy loam (10% clay in sand);
• loams (30% clay in sand);
• clay (hard in dry pieces and viscous when wet);
• vegetable (with inclusions of peat).

The saturation of the soil with moisture determines the strength of frost heaving. If drops of water collect between solid particles, then at negative temperatures, in areas of the middle zone, where the lower freezing mark is 1.2–1.5 m, the soil can rise by 15–20 cm. The length of the “support” piles is 2.1 m will allow them to rest against the fixed layer. The above-ground strip foundation will be outside the zone of influence of frost heaving.

The structure and moisture content of rocks at a construction site are determined using a garden or construction auger. According to the instructions, samples are taken in several places from pits with a depth of at least 2 m. If the samples consist of dry sand (fractions over 0.5 mm), gravel or pebble soil, a “hanging” pile foundation is connected to a shallow foundation. The reinforced concrete strip is laid to a depth of 30-40 cm. Sand or sand-gravel mixture (sand-gravel mixture) is first poured into the bottom of the trench.

Installation Guide for Bored Supports

Point supports, which are embedded in the soil layer, are divided into screw and pressed ones. The first are a metal barrel (pipe) with a diameter of 60 to 140 mm with blades at a pointed end. Strip foundations on screw piles are buried below the frost layer, so their length is 1.5–3.5 m. The blades increase the supporting area and make it possible to screw the structure into the ground with your own hands using a vertical gate. The diameter of the pile screw for flooded areas is 500-850 mm.

The cost of a bored foundation depends on the formwork for pouring a reinforced concrete pile. After preparing the pit, a pipe made of asbestos cement, metal, plastic or roofing felt is inserted into it. The internal cavity is reinforced and filled with concrete. The use of waterproofing material as permanent formwork is the most economical method of forming piles:

1. the well is deepened 30 cm below soil freezing using a manual or mechanical drill;

2. sand is poured to the bottom;

3. vertical walls are lined with roofing felt;

4. part of the cardboard formwork, which rises 40 cm above ground level, is tied together with wire;

5. 2-3 rods of corrugated reinforcement 50 cm long above the edge of the roofing felt are inserted into the compacted sand;

6. The internal cavity is filled with concrete, which is pierced several times with a long ramrod to release air;

7. After 7–10 days, the formwork for the grillage is installed.

Do-it-yourself pile-strip foundations from ready-made pipes are built in the same way, although the instructions contain several additional points. To form a stable shoe, part of the mixture is poured into the bottom of the well through a pipe and the mold is raised so that the solution saturates the sand cushion. The pile is fixed vertically until the base hardens. Then the support is reinforced and concreted.

Concrete consumption per 10 m pipe diameter:

• 100 mm – 0.1;
• 200 mm – 0.5;
• 300 mm – 1 m3.

Installation of monolithic tape on piles

The low cost of cellular concrete and the reduction in construction time explain the popularity of large-sized gas silicate and foam blocks. Due to the lightness of the porous material, the load on the base is significantly reduced compared to brickwork of the same volume. The foundation for a house made of foam blocks is mounted using a pile-and-tape scheme.

The number of supports with a cross-section of about 800 cm2 (trunk diameter 30 cm) for the grillage is calculated based on a load of up to 800 kg per piece, if the site is dominated by wet silty sand with a bearing capacity of 1 kg/cm2. A pile on dense layers with a resistance of 2 kg/cm2 will withstand 1600 kg. The total weight of all building structures and internal equipment of the living space is divided by the calculated load indicator with a margin of 30%. The number of piles is distributed on the plan, starting from the intersections of the external walls in increments of 1–2 m.

To fill the bored piles and base tape, moveable concrete is prepared in a ratio of 1:6 using Portland cement M500 and ASG. A plasticizer is added to the mixture to prevent the formation of pits and voids. The solution is mixed in a mechanical mixer, which is installed at the construction site.

Step-by-step instructions for installing a foundation made of bored piles and a reinforced concrete grillage:

1. Markings of load-bearing walls are made on the site;

2. remove the grassy layer around the perimeter of the building;

3. place pegs in the places where the piles are installed;

4. drilling wells;

5. The bottom is compacted with coarse sand;

6. formwork pipes are inserted into the holes;

7. the forms are reinforced and filled with concrete;

8. A welded two-tier tape frame is tied to the upper parts of the rods;

9. install a sealed formwork with a floor 20–30 cm above the ground level, covered with a waterproof film;

10. Place bars under the reinforcement so that it does not come into contact with the wood;

11. Pouring concrete is poured and compacted with a vibrator.

Depending on weather conditions, the mixture hardens in 4–5 weeks. The formwork is removed and a sliding fence made of flat slate is installed using expansion joint technology. The bottom sheet is dug into the ground, and it serves as a limiter for the blind area. The top panel overlaps it and is attached with dowels to the tape.

Nuances of laying the foundation

1. The pile foundation is installed with a support spacing of 1 to 2 m.

2. Wells for pipes are dug 10–15 cm larger than their diameter. You can do the drilling yourself, which will reduce the cost of work.

3. Instead of sand, you can fill the bottom of the pit with ASG.

4. The outside of the pipe formwork is lubricated with bitumen mastic and wrapped with roofing felt.

5. Depending on the weight of the structure and the thickness of the walls, the strip foundation is 30–40 cm wide and up to 70 cm high.

6. If the formwork is installed from the ground, sand is poured into it or polystyrene is laid to raise the level of the monolith. The bedding is removed after 7–10 days.

7. A horizontal frame made of corrugated rods with a diameter of 10–16 mm is welded with vertical reinforcement 6–12 mm.

8. In hot weather, concrete is moistened for the first 5–7 days after pouring; in cold weather, it is sealed with heated water.

Common mistakes:

• Insufficient depth of piles in unstable soil, high degree moisture and frost heaving.
• Incorrect calculation of the number, diameter and installation pitch of foundation piles.
• Failure to maintain the gap between the grillage and the ground level in the case of dispersed soil.
• Lack of continuous waterproofing of the underground part.
• Weak reinforcement of piles and tape of a monolithic grillage.
• Fixed retractable suspended base.
• The use of concrete whose strength does not correspond to its functional purpose.
• Pouring mortar under adverse weather conditions.

Turnkey cost

*Materials, labor, equipment rental, transportation costs.

A team of specialists will help you make the combined foundation of a private house on a difficult site with your own hands. To ensure a strong structure, concrete is mixed from fresh cement according to the instructions on the packaging of a trusted manufacturer.