Building construction

Purpose

• Distribute the load

• Make the bearing surface uniform

• Prevent movement

• Increase stability

Ground Level

Super-structure

foundation

Distribute building load to the ground

Size and depth of a foundation is determined by:

Structure and size of building it supports

Nature and bearing capacity of the ground supporting it

The two basic types of

foundations:

Shallow Deep

Deep Foundation

DefinitionIt extends down through unsuitable or unstable soil to transfer building loads to a more appropriate bearing stratum of rock or dense sands and gravels.

Unlike shallow foundations, deep foundations distribute the load of into the ground vertically rather than laterally.

Cases• Weak soils near the surface

• Loads very high

• Soil stratum is not strong or stable

Example: Petronas Twin Towers in Malaysia

The Two Principal Types of Deep Foundations:

Pile Caisson

Pile

Pile Foundation

Definition

A system of end bearing or friction piles, pile caps and tie beams for transferring building loads down to a suitable bearing

Types

Piles may be of treated timber poles but for large buildings, steel H sections, concrete filled pipes, or precast reinforced or prestressedconcrete are more common.

Timber H-Sections Pipe Piles Precast Concrete

Cases

• Stratum of required bearing capacity is at greater depth

• Steep slopes

• Compressible soil

• Water-logged soil

• Soil of made-up type

Slope

Advantages

• Can be used for any type of structure and in any type of soil.

• Can be precast

• Can be used in places where it is advisable not to drill holes

Disadvantages• Must be reinforced

to withstand stresses

• Requires heavy equipment for handling and driving.

• Foundations of adjacent structures are likely to be affected due to the vibrations

Process and Machinery

Piles are driven into the earth by a pile driver, composed of a tall framework supporting machinery for lifting the pile in position before driving, a driving hammer, and vertical rails or leads for guiding the hammer

Pile driver

For driving piles into the ground

Driving Hammer

Drilling rig

Creates holes in the earth sub-surface

Classification of Pile Foundation

Based on Function

End-Bearing Piles Friction Piles

End-Bearing Pile

Depends principally on the bearing resistance of soil or rock beneath their feet for support.

Friction Bearing Pile

Depend principally on the frictional resistance of a surrounding earth mass for support.

Caisson Foundation

Definition

Formed by boring with a large auger or excavating by hand a shaft in the earth to a suitable bearing stratum and filling the shaft with concrete

Auger

Crane

Crane for filling caisson

Cases

• Suitable for underwater foundation where the foundation should be extended up to or below the river bed to obtain stability

• Often used when constructing bridge piers and other such foundations

Advantages

• Extended to large depths

• Cost is relatively less

• There is direct and easy passage to reach the bottom of caisson so any obstruction can easily be removed.

Disadvantages• Precautions should

be taken, otherwise it may lead to fatal accidents.

• Labor cost is high.

• If obstacles like boulders or logs are encountered, then progress becomes slow.

A temporary casing may be required to seal out water, sand or loose fill from the shaft during excavation

The base of a caisson may be enlarged into a bell shape to increase its bearing area and resist uplift from soil expansion. The bell may be excavated by hand or be formed by a bucket attachment to an earth auger that has a set of retractable blades

Some caissons are drilled into a stratum of solid rock in order to gain additional frictional support

Floating Foundation (Shallow)

Definition• Does not use footings

• Support on soft soil

• Consists of a stiff reinforced concrete slab

• Distributes the load by columns to the soil

Why is it called “floating”?Because it

"floats" on the soil.

Cases

• Often seen in warmer climates

Why?

Ground freezing and thawing is less of a concern

No need for heat ducting underneath the floor

• Common in garage floors and mobile home slabs

Process

Install reinforced steel rods or heavy wire mesh

(to prevent floor from cracking and breaking)

Pour concrete

Advantages

• Termites are not a problem

• Inexpensive

• Moisture barrier

• For areas with lower load bearing capacities

Disadvantages• Expansion not

possible

• Lack of underground access

• Exposes the building to flood damage in even moderate rains