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CHAPTER 2 SUBSTRUCTURE

2.1 Introduction
2.2 Building foundation - types and functions
2.3 Deep Foundation
spun 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

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 is
in 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 over a larger area. • To transmit the load uniformly under the structure. • To provide a firm. level and strong base over which the superstructure may be constructed.

. • To increase the stability of the structure by preventing its tilting or overturning against winds. earthquakes and uneven distribution of live load (Lateral Stability).Main functions of the foundations • To avoid any settlement or other movement that can cause damage to any part of the building (a stable foundation should bear the loads without sinking or settling more than an inch at the most).

Load Distribution Load Ground Level 45o .

big load need big foundation such as raft foundation or piling • Types of soil such as peat soil prefer piling or deep foundation • Economical / financial for number of building or story – (pad footing or pilling) .Type of foundation is selected based on • Loading of the building.

This also should evaluate the ability of the soil to support the ultimate loads.Type of foundation is selected based on • The loads that must be transferred from the structure to the soil strata supporting it. . • The capability of the structure that will safely transfer the loads from the superstructure to the foundation bed.

Type of foundation is selected based on • The possibility and extent of settlement of the soil due to the presence of mines and quarries in the vicinity. • The ability to determine if the underground water has sulfates or other salts that can degrade the foundation materials. • The ability for engineers to fix the depth of the foundation. .

Factors That Need To Be Considered in the Foundation Design • For more safety precaution use factor of safety FOS 3 • Increase number of bore hole or suffient number of borehole so that the result of the report is more accurate. – Choose the critical point load for borehole – Every end of the building – Supervise the S.I properly make sure no mistake .

Factors That Need To Be Considered in the Foundation Design • For the safety of the foundation design use the lowest of bearing capacity value • The engineer must have good enough data for the S. . cutting or filling area.I such as previous soil report. • Engineer also must make sure the original ground level and purposed level or formation level while designing the foundation.

Factors That Need To Be Considered in the Foundation Design • The correct parameter is important to prevent from foundation failure that may occur causing building collapse. It will cause a big loss of material and even peoples life. .

Highland Tower Collapse .

Types of Foundation Shallow foundation :• Spread Footings. • Bored pile. • Raft Foundation. . • Micro pile. Deep foundation :• Pile. • Square Pad Footing.

Strip Foundation • This type of foundation is also known as wall foundation or continues spread footing foundation. • It uses is to support load bearing wall. .

Continuous Spread Footing .

• This type of footing is commonly used to support the walls of aboveground circular storage tanks .

needs a foundation. whether big or small. • Every structure.Foundations Definition: • A foundation is a part of the structure which is in direct contact with the ground to which the loads are transmitted. . • The foundation carries the load of the building and provides it stability.

• The foundation transmits the loads imposed on the structure to the soil below it and therefore the type of soil used is very important. Even this settlement should be uniform under the entire building. the foundation is designed as either shallow or deep. . • A stable foundation should bear the loads without sinking or settling more than an inch at the most. • Depending upon whether the soil is stable or loose and unstable and the type and size of the structure.

Construction Terminology • The foundation is known as the substructure (under the soil structure) and the building itself is known as the superstructure (above ground structure). • We can say that the main function of the foundation is to support the load of the superstructure and transmit the load evenly to the soil .

Main Functions • To distribute the load of the structure over a larger area. level and strong base over which the superstructure may be constructed. • To provide a firm. • To avoid any settlement or other movement that can cause damage to any part of the building. . • To transmit the load uniformly under the structure.

earthquakes and uneven distribution of live load.• To increase the stability of the structure by preventing its tilting or overturning against winds. (Lateral Stability) .

Load Ground Level 450 Figure 1.1 Foundation .

EQUILIBRIUM .Forces pushing down must equal the forces pushing up .

Heave If the forces pushing up is greater than the forces pushing down the building will be pushed upwards – HEAVE Subsid e If forces pushing down is greater than the forces pushing up the building will sink – SUBSIDENCE .

Problems if the rules are not followed The load spreads at about 400 through the foundation .

A live load or imposed load is a movable. .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. temporary or transferable load. people walking or children jumping. This can include moving vehicles. • The following are the different types of loads that act on the building foundation: • Live Load (Qk) .

It is the non. . • Wind Load (Wk) .Types of loads • Dead Load (Gk).This load is permanent and immovable.transferable load of the structure itself. • Snow Load . hilly areas.This load is considered when the structure is situated in snowy.This load is applicable when the structure is tall.

000 600 100 to 300 Less than 100 300 to 600 100 to 300 Less than 75 Typical allowable bearing values . compact Medium dense sand Loose fine sand Hard clay Medium clay Soft Clay 10.000 2. sand and gravel.000 600 to 2.000 to 4.Rock or soil Typical bearing value (kN/m2) Massive igneous bedrock Sandstone Shales and mudstone Gravel.

This soil is compressible and yields when loaded. Small buildings or ordinary structures can be built on these types of soils.Types of Soils The following are the different types of soils on which foundations are constructed: • Soft soils . . Examples are clayey soil and loam.

They can withstand heavy loads without yielding. • Hard or rocky soils . . Multistoried buildings and water reservoirs are designed on such soils.• Spreading soils . Examples of this type of soil are sand and gravel.These are incompressible and strong soils.These are non-cohesive soils.

Shallow Foundation Types of Foundation Strip Footing Pad Footing Raft Foundation Spun Pile Deep Foundation Micro Pile Bakau Pile Bore Pile .

the type of soil and the type of material used. • They are classified into shallow and deep foundations. .• The type of foundation used is selected based on the type of the structure that has to be built.

.Shallow Foundations – for low-rise construction • When the foundation is placed just below the superstructure. it is known as shallow foundation. • The purpose of these is to transmit the loads of the superstructure over a wider area. • These foundations are suitable for small buildings.

. and piers. -the common reasons are because of large design loads. -distinguished from shallow foundations by the depth they are embedded into the ground. a poor soil at shallow depth. -deep foundations including piles. The naming conventions may vary between engineering disciplines and firms. caissons. or site constraints (like property lines). drilled shafts.A deep foundation is a type of foundation.

-Deep foundations can be made out of timber. reinforced concrete and pre-tensioned concrete. -Deep foundations can be installed by either driving them into the ground or drilling a shaft and filling it with concrete. mass or reinforced . steel.

Spread/Strip Footings • Also known as footer or simply a footing. • An enlargement at the bottom of a column or bearing wall that spreads the applied structural loads over a sufficiently large soil area. . each column and each bearing wall has its own spread footing. • Typically.

• For large structures with exceptionally good soil or shallow bedrock. .Characteristic of Spread Footings • Low Cost • Ease of construction • For small-medium size structures with moderate-good soil.

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.• Spread footing may be built in different shapes and sizes to accommodate individual needs.

Types of spread footings based on size 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 .

CONSTRUCTION ACTIVITY ON PAD FOOTING OR STRIP FOOTING • PEGGING • EXCAVATION WORKS • PROVIDING A MATERIALS – REBAR – FORMWORK – CEMENT – SAND – AGGREGATE • FORMWORK – EXCAVATE A WORKING SPACES FOR BETTER CONSTRUCTION .

• REINFORCEMENT INSTALLATION • CONCRETING – – – – MIXING POURING CURING TESTING .

• Each block of concrete is overlapped by the next block. • The foundation trenches are excavated in steps and each step is filled with some concrete. • Square footings usually support a single centrally-located column. and so on. . • When the structure is to be constructed on the hill slopes. this type of foundation is used.Stepped Foundation (Spread Footings) • This type of foundation is one of the pad foundation types.

Step no greater than 450 mm Overlap to be equal to or greater than the depth of the concrete foundation .

Square Footings .

the two walls or columns of a superstructure are provided with a single combined footing.Combined Footing Foundation • In this type. . • This is designed so that the center of gravity of the supporting area is in proportion to the center of gravity of the tow column loads. • These can be rectangular or trapezoidal in shape.

.These are usefull when columns are located too close together for each to have its own footing.

. • These are useful when obstructions prevent construction of a square footing with a sufficiently large base area and when large moment loads are present. where L is the longest dimension.Rectangular Spread Footings • It have plan dimension of B x L.

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flagpoles. .Circular Spread Footings • This foundation are round in plan view. • These are more frequently used as foundation for light standard. and power transmission line. they may be have more like a deep foundation. • If these foundation extend to a large depth.

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• It uses is to support bearing wall.Continuous Spread Footings • This type of foundation is also known as wall foundation or strip foundation. .

Ring Spread Footings • This footing are continuous footing that been wrapped into a circle. • This type of footing is commonly used to support the walls of above-ground circular storage tanks. .

Ring Spread Footing .

Raft Foundation
• Also known as Mat Foundation or Floating
Foundation.
• 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.

• This consists of reinforced concrete
slabs covering the entire area of
construction, like a floor.
• Always made of reinforced concrete.

Consideration of using Raft
Foundation
• The structural loads are so high.
• The soil condition is so poor.
• The bottom of structure is located below
groundwater table.
• Raft foundation are more easier to
waterproof.

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weight of the mat is a factor here -Mat foundations are easier to waterproof .Conditions for Mat Foundations -Structural loads require large area to spread the load -Soil is erratic and prone to differential settlements -Structural loads are erratic -Unevenly distributed lateral loads -Uplift loads are larger than spread footings can accommodate.

it is important to reach soil stratum below the scour depth of the rivers to prevent settlement. it is necessary to take the foundation deeper to reach the stable stratum.Deep Foundation • In cases where the soil stratum is not stable or strong. • For instance. in cases of river bridges. .

Deep Foundation



Spun pile
Micro pile
Bakau pile
Bore pile

Pile Foundation


Pile foundations are the part of a structure used to carry and
transfer the load of the structure to the bearing ground located at
some depth below ground surface.
The main components of the foundation are the pile cap and the
piles.
Piles are long and slender members which transfer the load to
deeper soil or rock of high bearing capacity avoiding shallow soil of
low bearing capacity
The main types of materials used for piles are wood, steel and
concrete. 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 transmitting
characteristic piles are classified accordingly.

Function of piles
As 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 have
adequate bearing capacity. If the results of site
investigation show that the shallow soil is unstable
and weak or if the magnitude of the estimated
settlement is not acceptable a pile foundation may
become considered. Further, a cost estimate may
indicate that a pile foundation may be cheaper
than any other compared ground improvement
costs.

Piles are a convenient method of foundation for works over water. and the construction should be built on pile foundations. it is likely that the bearing capacity of the shallow soil will not be satisfactory. Piles can also be used in normal ground conditions to resist horizontal loads.Function of piles As with other types of foundations. such as jetties or bridge piers. the purpose of a pile foundations is: • In the cases of heavy constructions. .

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 .

.End bearing piles • These piles transfer their load on to a firm stratum located at a considerable depth below the base of the structure and they derive most of their carrying capacity from the penetration resistance of the soil at the toe of the pile. Load is transmitted to the soil through friction or cohesion. if it is in either air or water. Even in weak soil a pile will not fail by buckling and this effect need only be considered if part of the pile is unsupported. i.e. • The pile behaves as an ordinary column and should be designed as such.

End bearing piles • But sometimes. This. Negative skin friction is caused by the drainage of the ground water and consolidation of the soil. sometimes have considerable effect on the capacity of the pile. the soil surrounding the pile may adhere to the surface of the pile and causes "Negative Skin Friction" on the pile. . The founding depth of the pile is influenced by the results of the site investigate on and soil test.

End bearing piles .

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• The process of driving such piles does not compact the soil appreciably. . • These types of pile foundations are commonly known as floating pile foundations.Friction piles • These piles also transfer their load to the ground through skin friction.

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9m and 12m (Typical) Structural Capacity : 45Ton to 520Ton Material : Grade 60MPa & 80MPa Concrete Joints: Welded Installation Method : –Drop Hammer –Jack-In .Spun Pile • • • • • • Size : 250mm to 1000mm Lengths : 6m.

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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 .

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 .

and hence produced a grouted column of soil. • Piles can be produced by casting concrete in the void. • In unstable ground. but driven into a hole which is bored as casing is advanced. Alternatively the casing may be permanent. such as gravel the ground requires temporary support from casing or bentonite slurry. A different technique. which is still essentially non-displacement. Some soils such as stiff clays are particularly amenable to the formation of piles in this way. is to intrude.Bored piles • Bored piles (Replacement piles) are generally considered to be non-displacement piles a void is formed by boring or excavation before piles is produced. since the bore hole walls do not requires temporary support except cloth to the ground surface. a grout or a concrete from an auger which is rotated into the granular soil. .

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Borepile Cosiderations… • •Borepile Base Difficult to Clean • •Bulging / Necking • •Collapse of Sidewall • •Dispute on Level of Weathered Rock .

Micropiles • 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. b) by extending pile cap below water level .

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concrete or composite) The anticipated driving conditions The durability of pile material in specific environment The local availability of each pile type . steel.Factors to be considered in selecting pile t The required diameter The required length (limit: 18m) The applied loads Factors to be considered in selecting a pile type (timber.

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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)   .Advantages & Disadvantages bakau pile No Advantages Disadvantages 1 Low construction cost Medium axial loads (100 .

• Damage during driving can be controlled by: –Using lightweight hammers –Using steel bands near butt –Using a steel shoe on the toe –Pre-drilling .

Advantages & Disadvantages Spun ile No 1 Advantages Best suited for use as friction piles that Disadvantages 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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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)   .Advantages & Disadvantages Bore Pile No Advantages Disadvantages 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.

d=500 – 1200mm and H=6.24m – Specialized rigs – A-Shaped Frame Rigs .Drilled Equipments • Drilling Rigs – Truck-mounted drilling rig • For usual shaft.

• Drilling Tools  The helix-shaped flight auger (most common used) – 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 .

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 . Bucket augers – To collect cuttings in a cylindrical bucket – Used in running sands  Belling buckets – To enlarge the bottom of the shaft (bells or under reams)  Core barrels – To cut a circular slot.

economy and good reability .Drilled Techniques • Drilling in Firm Soils – Using dry method (open-hole method) – Most common used: simple.

• Steps: – Holes usually advance using conventional flight auger – Holes remain open without any special support – Check the open hole for cleanliness and alignment – Insert steel reinforcing cage – Pour the concrete .

• Usually in clean sands below the groundwater table.• Drilling in Caving (Cave-in) or Squeezing Soils – Caving: • The side of a hole which is collapse before or during concrete placement. .

. – Most common techniques: • Using casing • Drilling fluid (slurry method) using bentonite clay or attapulgite clay.– Squeezing: • The sides of hole bulging inward during or after drilling • Usually in soft clays and silts or highly organic soils.

Pile caps are thus incorporated in order to tie the pile heads together so that individual pile movement and settlement is greatly reduced. a pile 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 structure to the pile or group of piles. then the load further transfers to from soil External pressures on a pile are likely to be greatest near the ground surface.Pile Cap In the British Standard Code of Practice BS 8004. Thus stability of the pile group is greatly increased. pile cap transfers the load form the structures to a pile / pile group. Ground stability increases with depth and pressure. Generally. . is more vulnerable to movement and stress than the base of the pile. The top of the pile therefore.

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Pile caps and isolated piles are typically connected with grade beams to tie the foundation elements together. lighter structural elements bear on the grade beams while heavier elements bear directly on the pile cap.Foundations relying on driven piles often have groups of piles connected by a pile cap (a large concrete block into which the heads of the piles are embedded) to distribute loads which are larger than one pile can bear. .

– To tie the piles together so they can act as a unit.Pile cap • Function: – To distribute the structural loads to the piles. – To laterally stabilise individual piles thus increasing overall stability of the group – To provide the necessary combined resistance to stresses set up by the superstructure and/or ground movement .

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 .

SUMMARY • Importance of Piling Supervision • Typical Piling Problems Encountered • Present Some Case Histories .