Pile and ring beam foundation: Pile & Ring Beam | Piling & Structural Services Ltd

Pile-strip foundation

Table of contents

• 1 Features of the combined foundation
• 2 Technology of the pile-strip foundation
  • 2. 1 Marking
  • 2.2 Excavation
  • 2.3 Foundation pile
    • 2.3.1 Well drilling
    • 2.3.2 Reinforcement
    • 2.3.3 Casting
  • 2.4 Foundation strip
    • 2.4.1 Underlay
    • 2.4.2 Footing
    • 2.4.3 Waterproofing
    • 2.4.4 Insulation
    • 2.4.5 Formwork
    • 2.4.6 Reinforcement
    • 2.4.7 Concreting
  • 2.5 Waterproofing

  9 0005 2.6 Insulation

  • 2.7 Backfilling

Combined pile foundation used to enhance the bearing capacity. It is used exclusively on soils with low design resistance to prefabricated loads from the building. It is extremely complex in calculations that are not available to an individual developer.

Features of the combined foundation

For a specific project, the choice of foundation is influenced by the geology and topography of the site. With a height difference of 1 m between adjacent walls of the cottage, strip foundations are ineffective. They are subject to serious lateral loads. Therefore, pile-strip foundation (SLF) is selected on flat areas with a height difference within the specified limits.

Heaving forces are practically not taken into account when designing piles. However, a strip foundation of small depth is forbidden to be used on clay soils without ensuring the elimination of swelling. Otherwise, the soil exerts significant pressure on the sole of the MZLF, the tape may come off the piles, on which there are no such loads.

The bearing capacity of MZLF, even without calculations, is quite sufficient for prefabricated loads of 2-3 storey brick cottages. However, on silty sands, peat bogs, fresh, not naturally compacted, embankments, MZLF will inevitably sink into the soil annually.

Attention: It is for the latter case that the tape is placed on piles that pass through unstable horizons, resting on a layer with a high bearing capacity. Therefore, the MZLF can be reinforced with piles only when organizing drainage, insulating the blind area, the sole, or the entire perimeter of the building.

Pile-strip foundation technology

To reduce the construction budget, pile-strip foundation (SLF) is often built on its own. Concrete is made on site, the capacity of concrete mixers is usually not enough for pouring in one step. Therefore, a pile field is first made, then the MZLF is concreted. When ordering mixers, the structure can be made completely monolithic by laying the mixture in one go into the wells, then into the formwork of the tape.

Attention: Often a pile-strip foundation is called a grillage according to the pile heads. This design does not experience swelling forces, since there is always a distance between the base of the grillage and the ground. Beams only collect loads, distribute them to piles. The technology differs in calculations, operating modes.

Marking

The placement of full-scale axes for SLF uses standard technology, taking into account distances to significant objects:

• reference angle – binding to the red line of the road (3 m to the center of the carriageway of the lane, 5 m to the street of the village), the border of the neighboring site (3 m)
• front facade – perpendicular or parallel to the street
• two side walls – triangle method for finding a right angle (sides 5 m, 3 m, 4 m)
• Diagonal verification – must match to within 1 cm

Attention: The pile-strip foundation is marked with strings / cords along cast-offs 1-1. 5 m from the edge of the trenches. floor support).

Excavation

Depending on the design of the lower floor ceilings, earthworks are carried out in the construction site:

The soil is removed from the site or distributed over the site. For MZLF, special equipment is usually not used.

Attention: At the same stage, perforated tubes are laid in geotextile for near-wall, ring drainage, depending on the level of GWL.

Pile part of the foundation

Bored piles are more difficult to manufacture than screwing in screw structures. Therefore, this technology will be considered. To fill the piles, it is necessary to drill wells to the bearing layer below the freezing mark. Install the formwork, place the reinforcing cage in it, lay the mixture, compact it with a vibrator.

Drilling wells

Due to the fact that manufacturers of motorized drills, hand tools for making holes in the ground produce equipment of 50 cm in diameter, the size of the wells is limited to this value. Depending on the width of the tape, the piles can be arranged in one or two rows. In practice, in individual construction, a single-row scheme is used, since the width of the MZLF does not exceed 60 cm.

For bored piles, there are several types of formwork, depending on the purpose, material:

• roofing material – rolled into a cylinder, the edges are fixed with staples, a budget option that does not provide protection against tangential forces from soil swelling
• asbestos-cement pipe – has additional bearing capacity, but does not provide concrete waterproofing
• polyethylene pipe – has a smooth outer surface, dramatically reduces pull-out loads on the pile, provides waterproofing of reinforced concrete

Attention: Regardless of the material, the pile formwork is usually not removable. This slightly increases the construction estimate, but increases the operational life of the structures.

Reinforcement

To increase the torsion strength of reinforced concrete, piles are reinforced with frames purchased from manufacturers or manufactured at the construction site. The technology has the following form:

• from reinforcement A400 with a periodic profile of 8 – 16 mm, bars are cut along the entire height of the pile + 30 cm for embedding into the tape (they are bent at a right angle in the upper part)
• rods are tied with ring, square, triangular clamps from A200 reinforcement without corrugation 6 – 8 mm in diameter

a Attention: The spacing of the clamps is 30 – 60 cm, it is preferable to fasten them with wire twists rather than welding. Unlike tape, reinforcement of piles with composite reinforcement is allowed.

Casting

For small drum volumes, the piles are cast separately from the belt. To do this, a funnel is installed on the formwork, the mixture is placed inside, compacted with the tip of a deep vibrator.

Normal compaction is evidenced by the cessation of the release of air bubbles, the concealment of large fractions of the filler, the appearance of cement laitance on the surface. The funnel should close immediately after the vibrator tip is removed.

Tape part of the foundation

For the manufacture of MZLF, standard technology is used. The only difference from the classic version is the rigid binding of the pile heads. To eliminate swelling, the perimeter of buildings for seasonal, periodic operation is covered under the sole of the tape with extruded polystyrene foam. For dwellings with constant heating, the heat insulator is laid under the sole, glued to the outer edges of the reinforced concrete structure, and placed under the blind area.

Underlayment

Replacing the heaving soil with crushed stone, sand allows you to partially reduce the forces of heaving under the sole. Non-metallic material is laid in layers (10 – 15 cm), rammed with a sole vibrator. To prevent mutual mixing with the soil, the underlying layer is laid on a geotextile sheet. With a low GWL, a budget sandy foundation pad is used. With high groundwater, crushed stone 5/20 mm is used.

Attention: The width of the underlying layer must be at least twice the size of the MZLF. If crushed stone is used, the surface is leveled with a small amount of sand.

Footing

A 5-7 cm screed of lean concrete is needed to level the surface, eliminate the leakage of cement laitance into the sand, and provide a surface for rolled waterproofing. The width of the footing is also twice the MZLF (coincides with the underlying layer). To save money, a mixture of B7.5 is used, there is no reinforcement of the screed.

Waterproofing

Several types of waterproofing can be used to protect reinforced concrete from getting wet:

• film – usually polyethylene with a thickness of 0. 15 mm or more, is laid or glued on a screed, the edges are launched onto the side walls of the trenches in order to paste over the side edges of them MZLF
• roll material – fused with a bituminous layer on the footing

Attention: The waterproofing must be two layers. The overlap of roll materials is 10 cm minimum.

Insulation

Depending on the heating mode of the dwelling, different schemes of foundation insulation are used:

• permanent heating – expanded polystyrene XPS or XPS under the sole of the tape, blind area + on the outer edge of the structure
• temporary heating – under the entire building, blind area + on the outer surface of the tape
• without heating – the inner side surfaces of the MZLF are pasted over + expanded polystyrene is laid under the whole house, tape, blind area

Caution: Due to heavy loads, low density PSB foam must not be used.

Formwork

Panels are adjacent to each other, aligned vertically, the upper edge is located 5 cm above the design level. To ensure the spatial rigidity of the structure, the formwork is pulled together with studs, reinforced with struts from the inside along the top of the shields, and jibs from the outside to the ground.

Boards are made from multi-layered plywood 10 – 12 mm or edged board 30 – 40 mm thick. The internal surfaces are covered with polyethylene to prevent leakage of the mortar mixture.

Attention: At the same stage, you can lay the vertical thermal insulation by pressing the Styrofoam against the sides of the formwork from the inside. In this case, the distance between the shields should be increased by the thickness of the insulation.

Reinforcement

To compensate for tensile forces that concrete cannot absorb without breaking, longitudinal reinforcing belts must be present in the bottom, upper part of the tape. Reinforcement is made according to the scheme:

• longitudinal rods of the lower, upper belt
• tying them every 30 – 60 cm (corners, straight sections, respectively) with rectangular clamps or horizontal, vertical jumpers
• anchoring at interfaces with L-shaped, U-shaped elements

Vertical rods protruding from piles bent at right angles at different levels. Some of the rods are connected to the lower belt of the MZLF frames, the other – to the upper bars.

Attention: It is forbidden to tie the frame bars with an overlap without bending to the adjacent side in the corners, junctions of internal load-bearing walls. The protective layer of concrete to prevent corrosion of the reinforcement is 1.5 – 7 cm (at the sole, on the sides, respectively).

Concreting

The mixture is placed inside the formwork in one direction, followed by a worker with a deep vibrator, removing air from the concrete, sinking the crushed stone inside. It is recommended to pour in one step, layer-by-layer concreting with an interval of more than 2 hours is prohibited.

After the concrete has been compacted and the setting has begun, shavings, sawdust or sand are placed on the upper edge of the belt. The wet compress is moistened periodically for the first three days.

Waterproofing

After stripping, all accessible concrete surfaces are covered with waterproofing materials according to the following technologies:

• plastering – moisture-resistant mixtures are applied to the surface or applied under pressure to provide a 2 – 4 cm layer without leveling
• coating – is carried out with bitumen, polymer, epoxy mastics in two layers
• pasting – with membranes, films or roll materials in two layers
• bulk insulation – impregnation with penetrating compounds that change, improve the structure of concrete through and through

Attention: Penetrating compounds can be introduced into the concrete during mixing. After that, the surfaces can not be processed, the default design becomes moisture resistant.

Insulation

Expanded polystyrene is glued to the vertical edges of the tape inside/outside, depending on the operating mode of the building. There is a technology of crushable thermal insulation, when the lower layer of insulation is glued to the tape, the upper one simply leans against the first layer covered with a film. It is pressed against the foundation with backfill materials, crushed during swelling, protecting the main contour of the thermal insulation.

Backfilling

It is recommended to fill the sinuses of the trenches with mixtures of AGM, sand, in which heaving is guaranteed to be absent. The thickness of the layer adjacent to the concrete structures must be at least 40 cm. Layered tamping is a must. Without this, the blind area will sag, collapse in the first months of operation.

Thus, the construction technology of the pile-strip foundation combines the production of a pile field, hard embedding of the heads inside the MZLF tape. To eliminate swelling of soils, ring or wall drainage is performed, the blind area, the outer edges of the tape or the entire perimeter of the building are insulated, depending on the mode of operation of the house.

calculation, how to make strapping, installation and reinforcement

Among the various types of foundations used in modern construction, a pile foundation can be especially distinguished. It is used in cases where the soil on the site is mobile, unstable, loose. Or groundwater comes too close to the soil surface.

For example, building a house on sand is not very smart. This is where this type of foundation comes to the rescue, allowing you to build buildings on any type of soil. In this article, we will analyze the features of the pile foundation, and also consider how to build a pile foundation with your own hands.

A pile foundation is a combination of piles that go into the ground and a concrete base on which the building rests.

Concrete base can be:

• solid,
• circular.

Monolithic footing is a type of slab foundation resting on buried piles.

The ring sole is, in fact, a strip foundation, which can be:

• partially buried in the ground,
• is at ground level,
• is raised up a couple of tens of centimeters.

The main load falls on piles that go into the ground to a depth of 1 to 25 meters, depending on the condition of the soil.

The pile foundation is widely used in the construction of one-story buildings. In this case, it is not necessary to bury the piles deep, which makes it possible to install the pile foundation with one’s own hands. In practice, it is known that the construction of multi-storey buildings on sandy soils is also carried out using a pile foundation. In this case, the piles are driven to a sufficiently large depth, allowing you to reach a solid ground.

In general, the principle of the pile foundation is as follows. Buried piles are located above the soil surface, where they are connected using a grillage (foundation sole) into a single structure. Such tying of a pile foundation allows you to reliably protect the house from possible displacements and movements.

Justification and calculation of the pile foundation are made on the basis of survey work carried out at the site. Such work is carried out only by specialists who have special measuring equipment in their arsenal. The fact is that the settlement of the pile foundation depends on many reasons, which can only be calculated by knowing the characteristics of the soil at various depths in a given area.

Types of pile foundations

According to the method of deepening, piles are divided into 4 main types.

Screw piles. Special equipment is required to bury them. Heavy metal piles are used, resembling giant screws. They are screwed into the soil to a certain depth.

The pile material must be coated with a layer of anti-corrosion coating that prevents the destruction and oxidation of metal in the soil.

Driven piles. These are prefabricated pointed poles made of metal or reinforced concrete, which are driven into the soil using special vibrating devices.

Bored piles. This is a type of pile that is poured directly on the construction site. First, a hole of a certain depth and diameter is drilled in the soil. Then a waterproofing material and reinforcing elements are inserted into it, after which the well is poured with concrete. This makes it possible to build a house on a pile foundation independently, without the use of heavy equipment.

This is relevant in cases where the foundation does not require solid penetration. It is enough to drill a hole about 1 meter with a hand drill, and then equip a pile in it.

Submerged piles. They are used in the case when there are ready-made concrete or reinforced concrete pillars, under which holes of given sizes are drilled in the soil. Finished products are immersed in the soil and are piles.

Types of pile foundations by depth level:

• Foundation with retaining piles. Buried piles rest with their bases on a layer of solid soil and are securely fixed on it. This achieves the maximum level of stability of the building.
• Foundation with hanging piles. If it is impossible to reach the level of occurrence of solid layers of soil, then hanging piles are used. They are tightly recessed into the soil, which takes on the main load. The interplay of grillage and hanging piles allows satisfactory results to be obtained in the most unstable soils.

Pile foundation materials

Metal. This is an expensive material used primarily in industrial and commercial construction. It requires the use of expensive equipment.

Concrete and reinforced concrete. Most common pile materials. The installation of a pile foundation from these materials is possible even in private construction, and the cost of such piles is low.

Wood. In places where there is no problem with wood, and the buildings being constructed are also made of wood, such piles are very acceptable. A prerequisite for their use is the impregnation of wood with antiseptics and its reliable waterproofing.

Wooden piles

Pile foundations can be built by yourself. We will analyze such a foundation using the example of building a private garage on loose soil.

First, markings are made along the perimeter of the future building, and then holes for the piles are drilled.

The piles should protrude above the soil surface by approximately one third of the height of the planned strip foundation.