Areas of application and stages of work on the construction of a pile-slab foundation

Buildings in locations with unstable or weak soil conditions are supported by pile-slab foundations. To evenly distribute the weight of the structure and avoid settlement or structural damage, it combines components of slab and pile foundations.

There are usually multiple important phases involved in the construction of a pile-slab foundation. The first step in preparing a construction site is clearing the area and making sure the ground is stable enough to hold construction machinery. After that, the foundation pile locations are marked and dug out to the necessary depth while accounting for the requirements for load bearing and the state of the soil.

After the excavation is finished, piles are driven into the earth. These piles are driven deeply into the ground until they reach a stable layer, or bedrock. They are typically composed of steel or reinforced concrete. By taking this step, you can make sure the foundation can withstand soil movement and support the weight of the building.

A concrete slab is built on top of the piles once they are in place. This slab, which forms the building’s foundation, is strengthened and long-lasting by steel bars. In order to guarantee a level and even surface for the superstructure construction of the building, the slab is meticulously leveled and finished.

To sum up, the pile-slab foundation is a flexible option for building projects with difficult soil conditions. It guarantees the stability and longevity of the building by distributing the weight of the structure evenly and preventing uneven settling. Comprehending the phases entailed in its establishment is imperative to guarantee a prosperous and long-lasting base for any construction endeavor.

Construction device

The foundation is structurally made up of two load-bearing sections:

1. Monolithic slab.
2. Pile field.

The free-standing supports are covered by the upper portion of the load-bearing structure. The following is how the design structure’s weight is dispersed across the ground by the foundation elements:

• 80–85% of the weight is taken by the pile field;
• 15–20% – reinforced concrete slab.

Different kinds of piles are selected based on the starting conditions:

• screw;
• bored;
• driving.

Combined pile-grillage foundation with a monolithic slab

A pile-pile foundation featuring a grillage is an alternative form of prior support structure.

Crucial components:

1. Supports buried in the soil.
2. Grillage combining pile heads.
3. Monolithic slab connecting all elements of the system into a single supporting structure.

This system’s grillage is in charge of connecting the top and bottom portions of the base and distributing loads uniformly.

Both kinds of foundations have essentially the same structure. The pile-slab foundation of one of the structures is completely grounded, and the other has a grillage that keeps the monolith from coming into contact with the ground. In the latter instance, seasonal soil freezing shields the base from forces that could cause it to topple.

When and which one is better to choose?

When it comes to building multi-story buildings and industrial facilities, slab on piles are the preferred method when it comes to the stability and dependability of the load-bearing structure on unstable soils. The resistance of such a structure to horizontal and vertical loads emerging in the soil will vary.

A pile-grillage foundation with a slab can be used in more situations. The following situations can make use of the foundation thanks to the system’s design features:

• the structure has many heavy floors and partitions, which necessitates the need for even distribution of weight on the base;
• the building rests on subsiding and waterlogged soils;
• underground sources on the site are located close to the surface;
• construction is taking place in an area of ​​high seismic activity.

The foundation design features for the site’s severe geological properties are outlined in SP 24.13330.2011.

The pile-slab foundation is a strong option for difficult soil conditions in building construction. This article describes the key steps in the construction process and examines its many uses in both residential and commercial projects. Every stage of the process, from precise pile installation and soil analysis to the casting of the reinforced concrete slab and site preparation, is essential to guaranteeing the stability and longevity of the foundation. Through comprehension of these phases, builders, contractors, and engineers can make well-informed choices to efficiently employ pile-slab foundations, augmenting the structural stability and longevity of building endeavors.

Preparation and design

Prior to design, the site’s attributes are examined, specifically:

• type and physical and mechanical properties of soil;
• degree of heaving of land masses;
• depth of seasonal soil freezing;
• risks of flooding, landslides, etc.d.

Perform design load calculations, taking into account the structure’s operational conditions. Considering the information obtained:

1. Decide on the advisability of using a pile-slab or pile-grillage foundation with a slab.
2. Select building materials (grade of concrete, characteristics of reinforcement, etc.).P.).
3. Determined with the geometric dimensions of the power elements.
4. Calculate the optimal depth of the supports.
5. Calculate risks regarding settlement and various deformations.

Designing entails creating a drawing. The information in the graphic document is as follows:

• dimensions of the structure being built;
• cross sections of all power elements;
• dimensions of supports, slabs, grillage, blind area, ledges;
• location of piles taking into account the pitch;
• elements of waterproofing and thermal insulation;
• reinforcement features;
• utility lines and more.

Attached to the graphic document:

1. Specifications of all structural elements.
2. Installation plan.
3. Table of permissible loads.
4. Notes regarding base features.

Piles-slab foundation drawings:

Construction technologies

Prior to beginning foundation construction It is advised that you become acquainted with the legal specifications outlined in the pertinent documentation:

• SP 24.13330.2011,
• SP 50-102-2003,
• SNiP 2.02.03-85,
• SNiP 2.02.01-83,
• SP 63.13330.2018.

Several technologies are employed in the construction of the foundation type that is being presented.

1. For slab base.
2. For supporting piles.
3. For pile-grillage load-bearing structure.

Marking the site and arrangement of the pit

Along the pile field’s axes, markings are made:

• insert cast-offs into the ground at a distance of 1.5 m from the corners of the structure;
• pull the cords;
• mark the contour with lime mortar.

Fundamentals of digging a pit:

1. The grillage technology does not involve excavation of soil for a monolithic part of the foundation.
2. For a buried slab, dig a pit to the depth of soil freezing (2–2.5 m).
3. For ground and shallow slabs – 0.5 – 1.0 m, respectively, preparing a place for a sand-crushed stone cushion.

Installation of piles

The choice of supports determines the technology used to build a pile field. Regarding pile-slab foundation You can use the following kinds of piles:

• reinforced concrete driving units;
• bored reinforced;
• screw (metal or reinforced concrete).

Steps involved in installing driven piles made of reinforced concrete:

1. Make small recesses in places where power elements are installed.
2. Driving piles using special equipment.
3. Align the supports at the same height.
4. They break the concrete at the top of the pillar, leaving an outlet of reinforced rods for subsequent connection with the upper element of the foundation.

Screw pile installation:

1. Before screwing in the piles, their surface is covered with a waterproofing compound).
2. The piles are screwed in to a certain depth using special equipment (as a rule, the supports are larger in size and it is impossible to properly screw in the elements manually).
3. Align the piles at the same level horizontally (for metal pipes, the upper part with the technological hole is cut off, for reinforced concrete pipes, the concrete is broken to gain access to the rods).
4. Metal pipes are filled with concrete mortar, which will protect the metal from oxidation.

Installation order for bored piles:

• dig trenches in the ground;
• at the bottom of the pit a compacted cushion of sand is arranged;
• they build formwork (often they use sheet roofing felt, which will serve as a waterproofing layer for the supports);
• a reinforcing frame is placed in the well;
• fill the hole with concrete;
• pierce the solution with a rod to remove air bubbles.

In order to provide a stable supporting layer for the load-bearing structure, piles are driven down to the depth of hard rock.

In the video, technology for piling a pile-slab foundation is demonstrated.

Making a grillage

In contrast to a slab, the grillage needs to be a specific height above the ground to prevent frost heaving forces from "tearing" it away from the piles.

Because of their greater strength and extended lifespan, metal grillages or reinforced concrete are recommended for the construction of heavy structures.

Phases involved in building a grillage made of reinforced concrete:

• formwork installation;
• laying a waterproofing layer;
• reinforcement;
• grouting.

Features of reinforced concrete grillage for various types of piles are determined by the need for a rigid bond:

1. Screw metal rods: the heads are recessed into the body of the grillage by at least 5–10 cm.
2. Reinforced concrete pillars: connect the reinforcing frame of the tape with the release of rods from the lower power elements.

Setting up a metallic grillage:

• a frame made of a channel or I-beam is welded onto the pile heads, placing the metal element “on edge”;
• a layer of corrugated sheeting is laid on the lower shelves of the metal frame.

You can install the channel "flat" when installing a grillage with detachable formwork; welding the channel to the heads is not required. In this instance, the concrete has hardened and the wood grillage is disassembled.

How the stove works?

Technological phases of the foundation’s upper monolithic section’s construction:

1. Sand cushion device.
2. Installation of concrete screed (footing) without reinforcement.
3. Laying the waterproofing layer.
4. Installation of formwork (5–7 cm higher than the design mark).
5. Reinforcement.
6. Concreting.
7. After hardening, treat the slab with cold mastic or bitumen primer.

The reinforcement frame of the slab may be connected with free rods of reinforced concrete supports or grillage reinforcement, depending on the type of lower part of the pile-slab foundation.

Characteristics of putting in a monolithic concrete foundation slab on screw piles:

• a channel is welded to the pipe heads as a piping, maintaining one horizontal level;
• welds are cleaned and covered with a layer of paint and varnish;
• a rolled metal frame is welded on top, creating a supporting plane for corrugated sheets;
• formwork is built under the slab (the gaps between the horizontal and vertical planes are sealed with polyurethane foam);
• the reinforcement frame is laid;
• the inside of the formwork is filled with mortar;
• after the concrete has hardened, the slab is coated with a waterproofing compound.

Options for a foundation with grillage that provides damping space beneath the slab include:

1. Installation of permanent foam formwork instead of concrete base. When swelling, the material contracts without exerting pressure on the structural elements of the structure.
2. Installation of panel formwork – option for a suspended grillage (1–1.5 m above the ground), so that the formwork can be removed after the concrete has hardened.

In the video, a slab is installed on piles for a pile-slab foundation.

Cost per linear meter

No developer will choose to set the price in advance because there are numerous variables that affect construction costs. You can concentrate on the average price of a slab foundation linear meter added to the pile and grillage base indicator:

Base type	Cost, rub./m3
Slab on screw piles	12000
Slab on bored piles	13800
Slab on driven reinforced concrete piles	15870
Slab on a pile-grillage foundation (with reinforced concrete flight deck)	17800
Slab on a pile-grillage foundation (with channel strapping)	16800

Common mistakes and tips on how to avoid them

Slab-pile foundation installation is a difficult and labor-intensive procedure best left to the expertise of licensed builders. Wherein the client must guarantee that employees don’t commit frequent errors:

1. Refusal of an additional waterproofing layer when the foundation slab is the floor of the lower floor. To reduce heat loss, experts advise laying a layer of clay between the ground and the sand cushion, and a sheet of foam plastic directly under the slab.
2. Pouring the solution in several stages. The problem is related to the significant volume of concrete required for construction. When the solution is supplied in parts, it gradually begins to harden and as a result, seams are formed, reducing the strength and rigidity of the foundation. As a rule, concrete is fed simultaneously through special chutes, avoiding impacts. The solution is then vibrated to remove air and maximize compaction.
3. The use of heaters to speed up the hardening of concrete. As a result, the slab turns out to be heterogeneous in composition, and the design strength of the base is reduced.

This site contains all of the information you require regarding the layout and building of a pile foundation.

Areas of Application

Stages of Work

A pile-slab foundation is ideal for areas with unstable soil, where traditional foundations might not hold well.

1. **Site Preparation**: Clear the site and excavate to the required depth. 2. **Pile Installation**: Drive or drill piles into the ground until they reach stable soil or bedrock. 3. **Concrete Pours**: Pour concrete into the excavated area around the piles to form the slab. 4. **Curing**: Allow the concrete to cure properly for strength and stability. 5. **Finishing**: Grade and backfill around the foundation to ensure proper drainage and stability.

There are several important steps involved in constructing a pile-slab foundation, which is used in many different types of building projects. Sites with unstable soil conditions or high water tables are best suited for this kind of foundation. It ensures stability and avoids uneven settling by spreading a structure’s weight across several piles.

Before building a pile-slab foundation, the site must be thoroughly inspected. To choose the best location and depth for the piles, engineers consider the characteristics of the soil, the levels of groundwater, and the overall topography. This stage is critical because it affects the stability and longevity of the foundation directly.

The pile installation stage of foundation construction then begins. Usually composed of steel or concrete, piles are driven deeply into the ground until they meet bedrock or stable soil. To guarantee that each pile can sustain the intended load of the structure above, this process necessitates accuracy. It’s a labor-intensive task that requires specific tools and knowledge.

The slab casting stage starts as soon as the piles are firmly in position. In order to create a solid base known as the slab, concrete must be poured over the tops of the piles. To increase the slab’s strength and longevity, reinforcement bars are frequently incorporated into it. Ensuring uniform support throughout the entire structure requires proper slab leveling and curing.

In summary, building a pile-slab foundation is a methodical process that begins with careful planning and results in a sturdy base that can support buildings under a variety of environmental circumstances. Because of its adaptability and efficiency, it’s a top option for regions with unstable soil or high water tables, giving engineers and builders a dependable way to create sturdy, safe structures.

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