03 Chapter 2 Substructure BFC21002

8/3/2019 03 Chapter 2 Substructure BFC21002

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CHAPTER 2 SUBSTRUCTURE2.1 Introduction2.2 Building foundation - types and functions

2.3 Deep Foundationspun pile, micro pile, bakau pile,bore pile and pile cap

2.4 Shallow Foundation

pad footing, raft foundation,strip foundation

2.5 Column, stump, ground beam


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What is Substructure?

The lowest portion of the building structure.

Usually located below the ground level.

A foundation is a part of the structure which isin direct contact with the ground to which the

loads are transmitted.


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Main functions of the foundations

To distribute the load of the structure overa larger area.

To transmit the load uniformly under thestructure.

To provide a firm, level and strong baseover which the superstructure may beconstructed.


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Main functions of the foundations

To avoid any settlement or othermovement that can cause damage to anypart of the building (a stable foundation

should bear the loads without sinking orsettling more than an inch at the most).

To increase the stability of the structure by

preventing its tilting or overturning againstwinds, earthquakes and unevendistribution of live load (Lateral Stability).


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Load Distribution

Ground Level

Load

45o


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Type of foundation is selected basedon

Loading of the building, big load need bigfoundation such as raft foundation or piling

Types of soil such as peat soil prefer pilingor deep foundation

Economical / financial for number ofbuilding or story (pad footing or pilling)


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The loads that must be transferred fromthe structure to the soil strata supporting it.This also should evaluate the ability of the

soil to support the ultimate loads.

The capability of the structure that willsafely transfer the loads from the

superstructure to the foundation bed.


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The possibility and extent of settlement ofthe soil due to the presence of mines andquarries in the vicinity.

The ability for engineers to fix the depth ofthe foundation.

The ability to determine if the undergroundwater has sulfates or other salts that candegrade the foundation materials.


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Factors That Need To Be Consideredin the Foundation Design

For more safety precaution use factor ofsafety FOS 3

Increase number of bore hole or suffientnumber of borehole so that the result ofthe report is more accurate.

Choose the critical point load for borehole

Every end of the building

Supervise the S.I properly make sure nomistake


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For the safety of the foundation design usethe lowest of bearing capacity value

The engineer must have good enoughdata for the S.I such as previous soilreport, cutting or filling area.

Engineer also must make sure the originalground level and purposed level orformation level while designing thefoundation.


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The correct parameter is important toprevent from foundation failure that mayoccur causing building collapse. It will

cause a big loss of material and evenpeoples life.


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Highland Tower Collapse


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Types of Foundation

Shallow foundation :-

Spread Footings.

Square Pad Footing. Raft Foundation. Deep foundation :-

Pile.

Bored pile.

Micro pile.


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Strip Foundation

This type of foundation is also known aswall foundation or continues spreadfooting foundation.

It uses is to support load bearing wall.


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Continuous Spread Footing


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This type offooting is

commonlyused tosupport the

walls ofabove-groundcircular

storagetanks


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Foundations

Definition:

A foundation is a part of the structure which is in direct contact withthe ground to which the loads are transmitted.

Every structure, whether big or small, needs a foundation.

The foundation carries the load of the building and provides itstability.


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The foundation transmits the loads imposed on the structure to thesoil below it and therefore the type of soil used is very important.

Depending upon whether the soil is stable or loose and unstable

and the type and size of the structure, the foundation is designed aseither shallow or deep.

A stable foundation should bear the loads without sinking or settlingmore than an inch at the most. Even this settlement should be

uniform under the entire building.


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Construction Terminology

The foundation is known as the substructure (under the soilstructure) and the building itself is known as the superstructure(above ground structure).

We can say that the main function of the foundation is to supportthe load of the superstructure and transmit the load evenly to thesoil


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Main Functions

To distribute the load of the structure over a larger area.

To transmit the load uniformly under the structure.

To provide a firm, level and strong base over which thesuperstructure may be constructed.

To avoid any settlement or other movement that can cause damageto any part of the building.


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To increase the stability of the structure by preventing its tiltingor overturning against winds, earthquakes and unevendistribution of live load. (Lateral Stability)


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Figure 1.1 Foundation

Load

Ground Level

450


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Forces pushing downmust equal the forcespushing up -EQUILIBRIUM


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Heave

Subside

If the forces pushing up is greaterthan the forces pushing down thebuilding will be pushed upwards

HEAVE

If forces pushing down is greaterthan the forces pushing up the

building will sink

SUBSIDENCE


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Problems if the rules are notfollowed

The load spreads at about400 through the foundation


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Loads Acting on the Foundation The foundation has to bear more than just the load of the

superstructure.

A load can be defined as anything, which exerts pressure or

thrust on a structure.

The following are the different types of loads that act on thebuilding foundation:

Live Load (Qk) - A live load or imposed load is a movable,temporary or transferable load. This can include moving vehicles,people walking or children jumping.


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Types of loads

Dead Load (Gk)- This load is permanent and immovable. It isthe non- transferable load of the structure itself.

Wind Load (Wk) - This load is applicable when the structure istall.

Snow Load - This load is considered when the structure issituated in snowy, hilly areas.


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Rock or soil Typical bearing value(kN/m2)

Massive igneousbedrock

Sandstone

Shales and mudstone

Gravel, sand and gravel,compact

Medium dense sand

Loose fine sand

Hard clayMedium clay

Soft Clay

10,0002,000 to 4,000

600 to 2,000

600

100 to 300

Less than 100

300 to 600

100 to 300

Less than 75

Typical allowable bearing values


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Types of Soils

The following are the different types ofsoils on which foundations areconstructed:

Soft soils - This soil is compressible andyields when loaded. Examples are clayeysoil and loam. Small buildings or ordinary

structures can be built on these types ofsoils.


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Spreading soils - These are non-cohesivesoils. Examples of this type of soil are sandand gravel.

Hard or rocky soils - These areincompressible and strong soils. They canwithstand heavy loads without yielding.Multistoried buildings and water reservoirs

are designed on such soils.


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Bore Pile

Bakau Pile

Shallow Foundation Strip Footing

Types ofFoundation

Deep Foundation

Pad Footing

Micro Pile

Raft Foundation

Spun Pile


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The type of foundation used is selectedbased on the type of the structure thathas to be built, the type of soil and the

type of material used. They are classified into shallow and

deep foundations.


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Shallow Foundations for low-rise construction

When the foundation is placed just belowthe superstructure, it is known as shallowfoundation.

The purpose of these is to transmit theloads of the superstructure over a widerarea.

These foundations are suitable for smallbuildings.


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A deep foundation is a type of foundation.

-distinguished from shallow foundations by the

depth they are embedded into the ground.

-the common reasons are because of large designloads, a poor soil at shallow depth, or site

constraints (like property lines).

-deep foundations including piles, drilled shafts,caissons, and piers. The naming conventions may

vary between engineering disciplines and firms.


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-Deep foundations can be made out of timber,steel, reinforced concrete and pre-tensioned

concrete.-Deep foundations can be installed by eitherdriving them into the ground or drilling a shaft andfilling it with concrete, mass or reinforced


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Spread/Strip Footings

Also known as footer or simply a footing.

An enlargement at the bottom of a column orbearing wall that spreads the applied structural

loads over a sufficiently large soil area. Typically, each column and each bearing wall

has its own spread footing.


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Characteristic of Spread Footings

Low Cost

Ease of construction

For small-medium size structures withmoderate-good soil.

For large structures with exceptionallygood soil or shallow bedrock.


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Spread footing may be built in differentshapes and sizes to accommodate

individual needs.


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Types of spread footings based onsize and shape

No Types of Spread Footings Applicable

1 Square for a single centrally-located column

2 Rectangular when large moment load are present

3 Circular for light standards, flagpoles etc

4 Continuous for bearing walls

(wall/strip footings)

5 Combined when columns are close together

6 Ring for walls of above-ground circular storage tanks

7 Strap (cantilever footing) when very close to a property line/other structure


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CONSTRUCTION ACTIVITY ON PADFOOTING OR STRIP FOOTING

PEGGING

EXCAVATION WORKS

PROVIDING A MATERIALS

REBAR FORMWORK

CEMENT

SAND

AGGREGATE FORMWORK

EXCAVATE A WORKING SPACES FORBETTER CONSTRUCTION


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REINFORCEMENT INSTALLATION

CONCRETING

MIXING

POURING

CURING

TESTING


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Stepped Foundation (Spread Footings)

This type of foundation is one of the padfoundation types.

When the structure is to be constructed onthe hill slopes, this type of foundation is used.

The foundation trenches are excavated insteps and each step is filled with someconcrete.

Each block of concrete is overlapped by thenext block, and so on.

Square footings usually support a singlecentrally-located column.


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Step no

greater than450 mm

Overlap to be equal to orgreater than the depth of theconcrete foundation


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Square Footings


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Combined Footing Foundation

In this type, the two walls or columns of asuperstructure are provided with a singlecombined footing.

This is designed so that the center of gravity ofthe supporting area is in proportion to the centerof gravity of the tow column loads.

These can be rectangular or trapezoidal in

shape.


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Rectangular Spread Footings

It have plan dimension of B x L, where L isthe longest dimension.

These are useful when obstructions

prevent construction of a square footingwith a sufficiently large base area andwhen large moment loads are present.


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Circular Spread Footings

This foundation are round in plan view.

These are more frequently used asfoundation for light standard, flagpoles,

and power transmission line.

If these foundation extend to a largedepth, they may be have more like a deep

foundation.


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Continuous Spread Footings

This type of foundation is also known aswall foundation or strip foundation.

It uses is to support bearing wall.


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Ring Spread Footings

This footing are continuous footing thatbeen wrapped into a circle.

This type of footing is commonly used to

support the walls of above-ground circularstorage tanks.


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Ring Spread Footing


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Raft Foundation

Also known as Mat Foundation or FloatingFoundation.

Used where heavily constructed loads are

to be distributed over a large surface area. It is used where the soil is marshy, clayey

or soft, with weak bearing capacity.


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This consists of reinforced concreteslabs covering the entire area ofconstruction, like a floor.

Always made of reinforced concrete.

Consideration of using Raft


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Consideration of using RaftFoundation

The structural loads are so high.

The soil condition is so poor.

The bottom of structure is located belowgroundwater table.

Raft foundation are more easier towaterproof.


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Conditions for Mat Foundations

-Structural loads require large area to spreadthe load-Soil is erratic and prone to differentialsettlements

-Structural loads are erratic-Unevenly distributed lateral loads-Uplift loads are larger than spread footings canaccommodate; weight of the mat is a factor

here-Mat foundations are easier to waterproof


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Deep Foundation

In cases where the soil stratum is not

stable or strong, it is necessary to

take the foundation deeper to reachthe stable stratum.

For instance, in cases of river

bridges, it is important to reach soilstratum below the scour depth of the

rivers to prevent settlement.


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Deep Foundation

Spun pile

Micro pile

Bakau pile Bore pile


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Pile Foundation

Pile foundations are the part of a structure used to carry and transferthe load of the structure to the bearing ground located at somedepth below ground surface.

The main components of the foundation are the pile cap and thepiles.

Piles are long and slender members which transfer the load todeeper soil or rock of high bearing capacity avoiding shallow soil oflow bearing capacity

The main types of materials used for piles are wood, steel andconcrete. Piles made from these materials are driven, drilled or

jacked into the ground and connected to pile caps.

Depending upon type of soil, pile material and load transmittingcharacteristic piles are classified accordingly.


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Function of pilesAs with other types of foundations, the purpose of

a pile foundations is: to transmit a foundation load to a solid ground to resist vertical, lateral and uplift load A structure can be founded on piles if the soil

immediately beneath its base does not haveadequate bearing capacity. If the results of siteinvestigation show that the shallow soil isunstable and weak or if the magnitude of theestimated settlement is not acceptable a pilefoundation may become considered. Further, acost estimate may indicate that a pile foundationmay be cheaper than any other comparedground improvement costs.


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Function of piles

As with other types of foundations, the purpose ofa pile foundations is:

In the cases of heavy constructions, it is likelythat the bearing capacity of the shallow soil will

not be satisfactory, and the construction shouldbe built on pile foundations. Piles can also beused in normal ground conditions to resisthorizontal loads. Piles are a convenient methodof foundation for works over water, such as

jetties or bridge piers.


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Classification of pile with respect to load

transmission and functional behaviour

End bearing piles (point bearing piles)

Friction piles (cohesion piles )

Combination of friction and cohesion piles


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End bearing piles

These piles transfer their load on to a firmstratumlocated at a considerable depth belowthe base of the structure and they derive most oftheir carrying capacity from the penetration

resistance of the soil at the toe of the pile.

The pile behaves as an ordinary column andshould be designed as such. Even in weak soil apile will not fail by buckling and this effect needonly be considered if part of the pile isunsupported, i.e. if it is in either air or water.Load is transmitted to the soil through friction orcohesion.


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End bearing piles

But sometimes, the soil surrounding the pile mayadhere to the surface of the pile and causes"Negative Skin Friction" on the pile. This,sometimes have considerable effect on the

capacity of the pile. Negative skin friction iscaused by the drainage of the ground water andconsolidation of the soil. The founding depth ofthe pile is influenced by the results of the siteinvestigate on and soil test.


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End bearing piles


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Friction piles

These piles also transfer theirload to the ground through skinfriction.

The process of driving such pilesdoes not compact the soilappreciably.

These types of pile foundations

are commonly known as floatingpile foundations.


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Spun Pile

Size : 250mm to 1000mm Lengths : 6m, 9m and 12m (Typical)

Structural Capacity : 45Ton to 520Ton

Material : Grade 60MPa & 80MPaConcrete

Joints: Welded

Installation Method :Drop Hammer

Jack-In


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Spun Piles vs RC Square Piles


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Spun Piles vs RC Square Piles

Spun Piles have

Better Bending Resistance

Higher Axial Capacity

Better Manufacturing Quality

Able to Sustain Higher Driving Stresses

Higher Tensile Capacity

Easier to Check Integrity of Pile Similar cost as RC Square Piles


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Bored Piles

Size : 450mm to 2m Lengths : Varies

Structural Capacity : 80Ton to 2,300Tons

Concrete Grade : 20MPa to 30MPa(Tremie)

Joints : None

Installation Method : Drill then Cast-In-Situ

B d il


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Bored piles

Bored piles (Replacement piles) are generallyconsidered to be non-displacement piles a void is formedby boring or excavation before piles is produced.

Piles can be produced by casting concrete in the void.Some soils such as stiff clays are particularly amenable

to the formation of piles in this way, since the bore holewalls do not requires temporary support except cloth tothe ground surface.

In unstable ground, such as gravel the ground requirestemporary support from casing or bentonite slurry.

Alternatively the casing may be permanent, but driveninto a hole which is bored as casing is advanced. Adifferent technique, which is still essentially non-displacement, is to intrude, a grout or a concrete from anauger which is rotated into the granular soil, and henceproduced a grouted column of soil.


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Borepile Cosiderations

Borepile Base Difficult to Clean

Bulging / Necking

Collapse of Sidewall

Dispute on Level of Weathered Rock

Micropiles


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p

Size : 100mm to 350mm Diameter

Lengths : Varies Structural Capacity : 20Ton to 250Ton

Material : Grade 25MPa to 35MPa Grout

N80 API Pipe as Reinforcement

Joints: None

Installation Method :

Drill then Cast-In-Situ

Percussion Then Cast-In-Situ


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Protecting timber piles from decay:a) by pre-cast concrete upper section above water level.


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a) by pre cast concrete upper section above water level.b) by extending pile cap below water level


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Factors to be considered inselecting a pile type

(timber, steel, concrete or composite)

The applied loads

The required diameter

The required length(limit: 18m)

The anticipateddriving conditions The durability of pilematerial in specific

environment

The local availabilityof each pile type

Factors to be considered in selecting pile type


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Advantages & Disadvantages


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g gbakau pile

No Advantages Disadvantages

1 Low construction cost Medium axial loads (100 - 400 kN)

2 Used as waterfront structures Susceptible to decay

3 For light driving conditions

Susceptible to damage when

driving

(in loose sands and soft to medium clays)


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Damage during driving can becontrolled by:

Using lightweight hammers

Using steel bands near butt

Using a steel shoe on the toe

Pre-drilling



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Spun ile


1 Best suited for use as friction piles that Expensive to splice and cut

don't meet refusal during driving

(refusal: pile can't be driven any further, so

it becomes necessary to cut off the portion)

2 Best suited for toe-bearing piles where the Difficult to cut

required length is uniform and predictable

3 Less expensive than steel piles Succeptible to damage during handling

or driving

4 Have a large load capacity Not suited for hard driving conditions


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Bore Pile


1 Less costs of mobilizing and demobilizing a drill rig Dependent on contractor's skills

2 Less noise and vibration Lower unit end bearing capacity

3 Soils excavated can be observed and classified Expensive for full-scale load test

during drilling

4 Size of shafts can easily be changed during const.

5 Can penetrate soils with cobbles, boulders and

many types of bedrock

6 Possible to support each column with one large

shaft (no pile cap)

Drilled Equipments


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Drilled Equipments

Drilling Rigs Truck-mounted drilling rig

For usual shaft, d=500 1200mm and H=6.24m

Specialized rigs A-Shaped Frame Rigs


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Drilling Tools

The helix-shaped flight auger (most commonused)

Effective in most sols and soft rocks

Augers with hardened teeth and pilot stingers Effective in hardpan or moderately hard

rock

Spiral-shaped rooting tools

Help loosen cobbles and boulders

Bucket augers

T ll t tti i li d i l b k t


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To collect cuttings in a cylindrical bucket

Used in running sands

Belling buckets

To enlarge the bottom of the shaft (bells orunder reams)

Core barrels To cut a circular slot,creating a removable

core

Used in hard rock

Multi-roller percussion bits To cut through hard rock

Cleanout buckets To remove final cuttings from hole

Drilled Techniques


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Drilled Techniques

Drilling in Firm Soils Using dry method (open-hole method)

Most common used: simple, economy and

good reability


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Steps: Holes usually advance using conventional

flight auger

Holes remain open without any specialsupport

Check the open hole for cleanliness andalignment

Insert steel reinforcing cage Pour the concrete


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Drilling in Caving (Cave-in) or SqueezingSoils

Caving:

The side of a hole which is collapse beforeor during concrete placement.

Usually in clean sands below thegroundwater table.


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Squeezing: The sides of hole bulging inward during or after

drilling

Usually in soft clays and silts or highly organic

soils.

Most common techniques:

Using casing

Drilling fluid (slurry method) using bentonite clay orattapulgite clay.


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Pile Cap In the British Standard Code of Practice BS 8004, apile cap is defined as a concrete block cast on the head of a

pile, or a group of piles, to transmit the load from the structureto the pile or group of piles.

Generally, pile cap transfers the load form the structures to apile / pile group, then the load further transfers to from soil

External pressures on a pile are likely to be greatest near theground surface. Ground stability increases with depth andpressure. The top of the pile therefore, is more vulnerable tomovement and stress than the base of the pile. Pile caps are

thus incorporated in order to tie the pile heads together so thatindividual pile movement and settlement is greatly reduced.Thus stability of the pile group is greatly increased.


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Foundations relying on driven piles often have

groups of piles connected by a pile cap (a largeconcrete block into which the heads of the pilesare embedded) to distribute loads which arelarger than one pile can bear.

Pile caps and isolated piles are typicallyconnected with grade beams to tie thefoundation elements together; lighter structural

elements bear on the grade beams while heavierelements bear directly on the pile cap.

Pile cap


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Pile cap

Function: To distribute the structural loads to the piles.

To tie the piles together so they can act as a

unit. To laterally stabilise individual piles thus

increasing overall stability of the group

To provide the necessary combinedresistance to stresses set up by thesuperstructure and/or ground movement


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SUMMARY

Importance of Preliminary Study Understanding the Site Geology

Carry out Proper Subsurface Investigation

that Suits the Terrain & Subsoil

Selection of Suitable Pile

Pile Design Concepts


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SUMMARY Importance of Piling Supervision

Typical Piling Problems Encountered

Present Some Case Histories

Documents

03 Chapter 2 Substructure BFC21002