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TYPES OF FOUNDATION

TYPES OF FOUNDATION

a) Shallow Foundation System

i) Spread Foundation

ii) Mat / Raft Foundation

b) Deep Foundation System

i) Pile iii) Diaphragham wall

ii) Pile walls iv) Caissons

SHALLOW FOUNDATION

Advantagesa) Cost (affordable)

b) Construction Procedure (simple)]

c) Material (mostly concrete)

d) Labour (doesn’t need expertise)

SPREAD FOOTING FOUNDATION

Also known as a footer or footing It’s an enlargement at the bottom of a column/

bearing wall that spreads the applied

structural loads over a sufficiently large soil

area. Each column & each bearing wall has its own

spread footing, so each structure may include

dozens of individual footings.

SPREAD FOUNDATION

The foundation consists of concrete slabs

located under each structural column and a

continuous slab under load-bearing walls. For the spread foundation system the

structural load is literally spread out over a

broad area under the building Most common type of foundation used due

to their low cost & ease of construction. Most often used in small to medium size

structure with moderate to good soil condition.

Spread footings may be built in different

shapes & sizes to accommodate individual

needs such as the following:

a) Square Spread Footings / Square Footings

b) Rectangular Spread Footings

c) Circular Spread Footings

d) Continuous Spread Footings

e) Combined Footings

f) Ring Spread Footings

a) Square Spread Footings / Pad Foundation

- support a single centrally located column

- use concrete mix 1:2:4 and reinforcement

- the reinforcement in both axes are to

resist/carry tension loads.

PAD FOUNDATION

b) Rectangular Spread Footings

- Useful when obstructions prevent

construction of a square footing with a

sufficiently large base area and when

large moment loads are present

c) Circular Spread Footings

- are round in plan view

- most frequently used as foundation for

light standards, flagpoles and power

transmission lines.

d)Continuous Spread Footings / Strip Foundation

- Used to support bearing walls

e) Combined Footings

- support more than one column

- useful when columns are located too close

together for each to have its own footing

f) Ring Spread Footings

- continuous footings that have been wrapped into a

circle

- commonly used to support the walls above-ground

circular storage tanks.

- The contents of these tanks are spread evenly

across the total base area and this weight is probably

greater that the tank itself

- Therefore the geotechnical analyses of tanks usually

treat them as circular foundations with diameters

equal to the diameter of the tank.

Ring Spread Footings

RAFT FOUNDATION

A foundation system in which essentially the

entire building is placed on a large continuous

footing. It is a flat concrete slab, heavily reinforced

with steel, which carries the downward loads

of the individual columns or walls.Raft foundations are used to spread the load

from a structure over a large area, normally

the entire area of the structure.

MAT/RAFT FOUNDATION

It is normally consists of a concrete slab

which extends over the entire loaded area. It may be stiffened by ribs or beams

incorporated into the foundation. Raft foundations have the advantage of

reducing differential settlements as the concrete slab resists differential movements between loading positions.

They are often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area.

Mat Foundation often considered to be

used when dealing with the following

conditions:a) The structural loads are so high or the soil

condition so poor that spread footings would be exceptionally large. As a general rule of thumb, if spread footings would cover more than 50% of the building footprint area, a mat or some type of deep foundation will usually be more economical.

b) The soil is very erratic & prone to excessive differential settlements. The structure continuity and flexural strength of a mat will bridge over these irregularities.

The same is true of mats on highly expansive soils prone to differential heaves.

c) The structural loads are erratic and thus increase the likelihood of excessive differential settlements. Again, the structural continuity and flexural strength of the mat will absorb these irregularities.

d) The lateral loads are not uniformly distributed through the structure and thus may cause differential horizontal movements in spread footings and pile caps.

The continuity of a mat will resist such movement.

e)The uplift loads are larger than spread footings can accommodate. The greater weight and continuity of a mat may provide sufficient resistance.

f) The bottom of the structure is located below the groundwater table, so waterproofing is an important concern. Because mats are monolithic, they are much easier to waterproof. The weight of the mat also helps resist hydrostatic uplift forces from the groundwater.

DEEP FOUNDATION

Extend several dozen feet below the building

a) Piles

b) Piers

c) Caissons

d) Compensated Foundation

PILES?????

A slender, structural member

consisting steel or concrete or timber. It is installed in the ground to transfer

the structural loads to soils at some

significant depth below the base of the

structure.

PILES

PILES FOUNDATION IS USED WHEN: The soil near the surface doesn’t have

sufficient bearing capacity (weak) to support

the structural loads. The estimated settlement of the soil exceeds

tolerable limits Differential settlement due to soil variability

or non-uniform structural loads is excessive Excavations to construct a shallow foundation

on a firm soil are difficult or expensive.

LOAD CAN BE TRANSFERRED BY PILE

TO THE GROUND BY 2 WAY THAT IS:

a) End Bearing Piles OR

- Pile will transmit load into the firm soil layer of the ground such as rock, gravel, very dense sand

b) Friction Piles

- Pile transmit the load from the structure to the penetrable soil by means of skin friction or cohession between the soil & the embedded surface of the pile.

There 2 type of End Bearing Piles That is Preformed Timber Pile & In-Site-Reinforced Concrete Pile

Friction Pile May Be Used To Support DownWard Load

TYPES OF PILES

a) Concrete Piles

i) Cast-In-Place Concrete Piles

ii) Precast Concrete Piles

iii) Drilled Shafts

b) Steel Piles

I) H-Piles ii) Cylindrical iii) Tapered

c) Timber Piles

d) Composite Piles

CAST IN PLACE CONCRETE PILES

i. Formed by driving a cylindrical steel shell into the ground to the desired depth and cavity of shell is filled with fluid concrete.

ii. The steel shell doesn’t contribute to the load transfer capacity of the pile.

iii. It’s purpose is to open a hole in a ground and keep it open to facilitate the construction of concrete pile. (same function as formwork)

iv. Vigilant quality control & good construction practice are necessary to ensure the integrity of cast-in-place piles.

Among the advantages of Cast-In-Place

Concrete are as follows:

Can sustain hard driving Resistant to marine organism Easily inspected Length can be changed easily Easy to handle and ship

PRECAST CONCRETE PILES

i. Usually have square/circular/octagonal cross sections.

ii. Fabricated in a construction yard from reinforced or pre-stressed concrete.

iii. Disadvantages of this pile are problems in transporting long piles, cutting and lengthening.

iv. It has higher capacity than timber piles.

STEEL PILES

i. It comes in various shapes & sizesii. Steel H-Piles are rolled steel sectionsiii. Steel pipe piles are seamless pipes that can

be welded to yield lengths up to 70m.iv. They are usually driven with open ends into

the soil.v. A conical tip is used where the piles have to

penetrate boulders & rocks.vi. However it needs to be treated before

embedded in corrosive environment.

TIMBER PILES

i. Have been used since ancient times

ii. Length of timber piles depends on types of trees used to harvest the piles,

iii. Common length are 12m

iv. It is susceptible to termites, marine organisms and rot within zones exposed to seasonal changes.

v. Eventhough it’s cheaper but it has low capacity and can’t take hard driving.

TYPES OF PILE CHOSEN DEPENDS

ON FOLLOWING FACTORS:a) What type of pile is readily available

b) Location & type of structure (magnitude of loading)

c) Ground Condition (soil type)

d) Cost

e) Durability

TYPES OF PILE CONSTRUCTION

a) Displacement Piles

- It cause the soil to be displaced radially as well as vertically as pile shaft is driven or jacked into the ground.

b) Non Displacement Piles

- It cause the soil to be removed and the resulting hole filled with concrete or a pre cast concrete pile is dropped into the hole and grouted in.

Displacement Pile

Replacement Pile / Non Displacement Pile

TYPES OF DISPLACEMENT PILES: Can be classified into different types base

on how they are constructed and how they are inserted.

There are 3 types as follows:

a) Totally Preformed Displacement Piles

(precast concrete or steel pile)

a) Driven & Cast-In-Place Displacement Pile

b) Helical Cast-In-Place Displacement Piles

a) Totally Preformed Displacement Piles - Precast Concrete or Steel Pileb) Driven & Cast-In-Place Displacement Pile - This type of pile can be of 2 forms. - The first involves driving a temporary steel tube with a closed end into the ground to form a void in the soil which is then filled with concrete as the tube is withdrawn. - The second type is the same except the steel tube is left in place to form a permanent casing.

c) Helical Cast-In-Place Displacement Piles

- This type of construction is performed using a special type of auger.

- The soil is however compacted, not removed as the auger is screwed into the ground.

- The auger is carried on a hollow stem which can be filled with concrete, so when the required depth has been reached concrete can be pumped down the stem & the auger slowly unscrewed leaving the pile cast in place.

METHOD OF INSTALLATION

a) Dropping Weight or Drop Hammers - commonly used method of insertion of

displacement pilesb) Diesel Hammers - Most suitable to drive pile in non cohesive

granular soilc) Vibratory Hammers or vibratory method of

pile driving - very effective in driving piles through non

cohesive granular soilc) Jacking Method Of Insertion

Diesel Hammer

Rapid controlled explosions can be produced by the diesel hammer.

The explosions raise a ram which is used to drive the pile into the ground.

Although the ram is smaller than the weight used in the drop hammer the increased frequency of the blows can make up for this inefficiency.

This type of hammer is most suitable for driving piles through non-cohesive granular soils where the majority of the resistance is from end bearing.

Vibratory Method of Pile Driving Vibratory methods can prove to be very

effective in driving piles through non cohesive granular soils.

The vibration of the pile excites the soil grains adjacent to the pile making the soil almost free flowing thus significantly reducing friction along the pile shaft.

However the large energy resulting from the vibrations can damage equipment, noise and vibration propagation can also result in the settlement of nearby buildings.

Pile Driving Rig - raise and temporarily support the pile that being driven and to support the pile hammer.

Pile Driving Rig

Dropping Weight / Drop Hammers

A weight approximately half that of the

pile is raised a suitable distance in a guide

and released to strike the pile head. When driving a hollow pile tube the

weight usually acts on a plug at the bottom

of the pile thus reducing any excess

stresses along the length of the tube during

insertion.

Pile Installation Using Drop Hammer

Jacking Method Of Insertion

Jacked Piles are most commonly used in

underpinning structures By excavating underneath a structure short

lengths of pile can be inserted and jacked

into the ground using the underside of the

existing structure as a reaction.

Jacking Method Of Insertion

NON DISPLACEMENT PILES

THERE ARE 4 TYPES THAT IS:

a) Small Diameter Cast-In-Place

b) Large Diameter Cast-In-Place

c) Partially Preformed Piles

d) Grout or Concrete Intruded Piles

PIERS

It’s a vertical bridge support. It’s a foundation for carrying a heavy

structural load which is constructed in site

in a deep excavation.

Among the things to be taken in consideration during construction of pier are as follows:a) Drilling through wet or caving soils may

need use of temporary steel casing. May also require the use of a tremie & a pump to dewater the hole & place concrete. This is more expensive and require a large diameter hole.

b) For the purpose of reinforcing, it’s difficult to get bars to the full depth of the pier with the proper concrete cover in deep holes.Use centralizes. Use large diameter bars versus more bars.

c) Don’t leave holes open for any length of time even in dry condition. Cuttings fall in or etc. Have concrete on site and fill right after drilling and cleaning.

Pier

Pier

Pier

Pumping Water Out Of The Hole For The Excavation Of The Pier

Constructing The Pier Framing

Completed Pier Framing

Post Footing & Detail

Ramp Is Installed

Ramp Is Bolted

Floor DeckingInstallation

Completed Pier

CAISSON FOUNDATION

WHAT IS CAISSONS?

It’s a prefabricated hollow box or cylinder. It is sunk into the ground to some desired

depth and then filled with concrete thus

forming a foundation. Most often used in the construction of bridge

piers & other structures that require foundation beneath rivers & other bodies of water.

This is because caissons can be floated to the job site and sunk into place.

Basically it is similar in form to pile

foundation but installed using different wayused when soil of adequate bearing strength

is found below surface layers of weak

materials such as fill or peat.It’s a form of deep foundation which are

constructed above ground level, then sunk to

the required level by excavating or dredging

material from within the caisson.

A caisson foundation consists of concrete

columns constructed in cylindrical shafts

excavated under the proposed structural

column locations Caissons are drilled to bedrock or deep into

the underlying strata if a geotech eng. find the

soil suitable to carry the building load.

It’s created by auguring a deep hole in the

ground. Then, 2 or more ‘stick’ reinforcing bar are I

inserted into and run the full length of the

hole and the concrete is poured into the

caisson hole. The caisson foundations carry the building

loads at their lower ends, which are often

bell-shaped.

Caissons

TYPES OF CAISSONS

Box Caissons Excavated Caissons Floating Caissons Open Caissons Pneumatic Caissons Sheeted Caissons

Reinforced Concrete Caissons

Caissons

Caisson As One Of The Elements In This Structure

TO BE CONTINUED, NEXT TOPIC