Foundation

Foundation

The lowest part of a building that transfers the load of the structure safely to the ground.

Functions of Foundation

• To distribute loads of the building evenly to the soil.

• To anchor the structure against uplift or sliding.

• To reduce settlement by spreading the load over a large area.

• To provide a level base for construction.

• To resist movement caused by changes in moisture, temperature, or soil pressure.

Foundation Materials

• Concrete

• Reinforced Concrete (R.C.)

• Stone/Rubble Masonry

• Brickwork structures

• Steel

• Timber

Foundation Size Depends on…

• The load of the structure.

• The type of soil (bearing capacity).

• The type of structure (single-story, multi-story, etc.).

• The depth of good bearing strata.

• Local building codes and design standards.

Foundation Size Rule of Thumb

• Foundation width is generally three times the wall thickness (for light buildings).

• The foundation depth should reach firm bearing strata, typically 2–4 ft for small structures.

Foundation Bed

The surface of the ground on which the foundation rests.

Characteristics of a Good Foundation Bed

• Uniform in strength and density.

• Free from organic matter and topsoil.

• Capable of withstanding the load without settlement.

• Properly levelled and compacted.

Preparation Steps

• Remove loose soil and debris.

• Compact the bed using rammers or rollers.

• Lay a blinding layer of lean concrete or sand (usually 3–4 in thick).

• Ensure proper leveling and marking before placing the foundation.

Shallow Foundation

Used when the bearing capacity of soil near the surface is adequate.

• Strip

• Pad

• Raft/Mat

• Combined

Deep Foundation

Used when good bearing soil is far below the surface.

• Pile

• Pier

• Caisson

Strip Foundation

Continuous strip of concrete under load-bearing walls. Common in residential buildings.

Pad Foundation

Isolated square or rectangular concrete block under a column or pier.

Raft (Mat) Foundation

A large concrete slab covering the entire building footprint; distributes load evenly on weak soils.

Combined Foundation

Supports two or more columns close together where pads would overlap.

Pile Foundation

Long, slender columns driven or bored into the ground to transfer loads to deeper strata.

Pier Foundation

Cylindrical columns supporting loads at a deeper level, similar to short piles.

Caisson Foundation

Used for bridges or marine structures, sunk into water-bearing strata.

Short Bored Pile

A type of shallow pile foundation, typically 10–20 ft deep, formed by boring small holes and filling them with concrete.

• The upper soil layer is weak.

• Loads are moderate.

• Excavation is difficult (e.g., near existing structures).

Construction Process

• Bore a hole using an auger (usually 10–20 ft deep).

• Place reinforcement cage (if needed).

• Pour concrete into the borehole.

• Allow to cure before placing load.

Advantages of Short Bored Pile

• Simple and economical for small buildings.

• Minimal vibration and noise.

• Can be constructed in restricted areas.

Piled Foundation

A deep foundation where long columns (piles) transfer loads from the building to deeper, stronger soil or rock layers.g

End-Bearing Piles

Transfer load directly to a strong soil or rock layer.

Friction Piles

Load is transferred through friction along the pile’s surface.

Composite Piles

Combine two materials (e.g., concrete and steel) for cost efficiency.

Driven Piles

Pre-cast and driven into the ground using a pile driver.

Bored Cast In Situ Piles

Holes are drilled, and concrete is cast in place.

Materials Used for Piles

• Concrete (plain or reinforced)

• Steel (H-piles, tubular piles)

• Timber (temporary or small works)

Advantages of Piles

• Suitable for heavy loads.

• Bypasses weak or compressible soils.

• Can be used underwater or near existing structures.

Disadvantages of Piles

• Expensive and requires skilled labor.

• Noise and vibration during driving.

Factors Affecting Foundation Selection

• Soil type and bearing capacity

• Load of the structure

• Water table level

• Type of building (height, purpose)

• Construction cost and time

• Environmental and site conditions