Foundation: Main Types and Methods of Installation

Types of Foundations

Modern construction uses the following types of foundations:

• strip (trench) foundations,
• pile foundations,
• slab (solid) foundations,
• column (pier) foundations.

A strip foundation is a monolithic concrete structure poured along the perimeter of a building and under load-bearing walls. It is reliable and relatively simple to install, making it a universal choice. Typically, strip foundations are poured into formwork with reinforcing steel.

A pile foundation uses concrete piles driven into the ground or poured in place. It is used for large buildings on unstable soils, transferring structural loads to deeper, more stable soil layers.

A slab (solid, floating) foundation is a massive reinforced concrete base covering the entire area of the structure. Due to high material consumption, especially in steel and concrete, this type is expensive and used mainly for small, low-rise homes. It suits all soil types and compensates for ground movement. Additionally, the foundation slab can serve as the floor base.

A column foundation consists of vertical supports placed at building corners and points of maximum load on floor slabs. Columns may be made of concrete, cement, brick, or metal. Its low cost and simplicity make it ideal for frame-type and wooden buildings.

Reinforcement of Foundations

Reinforcement in the foundation increases concrete’s load-bearing capacity. Two common methods are used: horizontal and vertical reinforcement.

Horizontal reinforcement uses parallel steel bars to resist pressure caused by uneven loads and soil frost heave.

Vertical reinforcement is used as the primary method in column foundations or as an addition to horizontal reinforcement when the foundation walls form a basement or ground floor.

Primary reinforcement bars range from 10 to 16 mm in diameter, tied together with thinner bars (8–10 mm). Connections can be made using electric arc welding or binding wire (3–4 mm diameter). Proper preparation is essential: rust or oil on the steel reduces bond strength with concrete.

Depth of Foundation Placement

Foundation depth depends on:

• soil type;
• groundwater level;
• building’s structural importance;
• depth of frost penetration;
• structural features (e.g., adjacent foundations, basement presence).

The minimum depth for foundations is 0.5 meters below ground level, assuming soil consists of coarse, medium, or gravelly sand. In other cases, foundations are typically placed below the frost line, but not less than 0.7 meters. A compacted base layer of sand, gravel, or crushed stone should be used as the first foundation layer.

How to Properly Pour a Foundation

After determining depth, digging trenches, and laying the base, install formwork made of nailed boards secured with supports. After placing the steel reinforcement cage, prepare the concrete mix.

Typically, M-200 concrete with medium-grained gravel or clean sand is used. First, mix concrete and sand in a 1:3 ratio, then add water in a 1:0.681 proportion. Mixing in a concrete mixer is recommended.

Professionally installed concrete is poured in one continuous pour. For DIY projects, pouring in sections is more practical. Two methods exist:

• Pour in horizontal layers across the entire formwork area. Ensure layers are not too thin, and avoid aligning layer boundaries with the steel reinforcement bars.
• Pour in separate sections, filling the formwork to full height. Use wooden partitions placed at a 45-degree angle to create stronger inclined joints.

While concrete cures, take the following steps:

• Remove air bubbles by poking the fresh mix with a steel rebar every centimeter.
• Protect the concrete from sunlight using roofing felt or plastic sheeting.
• Moisten the surface for even drying: every four hours for the first three days, and three times daily from day three to eight.

Concrete curing takes 28 days.

How to Level a Foundation to Zero

Leveling a foundation to zero means ensuring all surface points lie on the same horizontal plane. This is best done during concrete pouring.

Well-poured concrete naturally achieves a level surface. However, if corrections are needed, install at least four reference stakes at the foundation’s corners. Use long steel bars or wooden stakes as markers. Mark zero level using a spirit level, then secure a string (shoelace) at the marked height. This string serves as a guide for final leveling.

This is not the only method, but it is simple and effective.