Foundation for high rise

TYPES OF FOUNDATION

Phases of foundation design

Soil report

• Project site

• Geology

• Tectonics

• Geological specialties

• Hydro geology

• Hydrogeological specialties

• Ground water investigations

• Ground water

• Building pit

• Foundation

• Uplift / Buoyancy

• Interaction with neighboring structures

• Displacement

• Ground risk

Important Engineering parameters

• Strength

• Compressibility

• Shear stress • Iso shear lines upto 1/3 of applied force

• Pressure bulb

UBC (Clay)

• Very stiff boulder clays and hard clays • 420–650 kN/m2

• Stiff and sandy clays • 220–420 kN/m2

• Firm and sandy clays • 110–220 kN/m2

• Soft clays • 55–110 kN/m2

• Very soft clays • <55 kN/m2

UBC (Sand)

• Compact graded sands and gravels • 430–650 kN/m2

• Loose graded sands and gravel • 220–430 kN/m2

• Compact sands of consistent grade • 220–430 kN/m2

• Loose sands of consistent grade • 110–220 kN/m2

• Silts • 55–110 kN/m2

Plate Load Test

• Increment of 1/5 of anticipated Ultimate load

• Deflection measured upto 2mm in 24 hrs

Types of Foundations

Shallow Foundations versus Deep Foundations

Foundations

Shallow Foundations Deep Foundations

Spread Footings Mat Foundations Driven Piles Drilled Shafts Auger Cast Piles

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Mat/Raft Foundation

A foundation system in which essentially the entire building is placed on a large continuous footing.

Usually large concrete slab supporting many columns.

Commonly used as foundation for silos, chimneys, large machinery.

It is a flat concrete slab, heavily reinforced with steel, which carries the downward loads of the individual columns or walls.

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Mat Foundation

The spread footings cover over 50% of the foundation area because of large column loads.

The soil is soft with a low bearing capacity.

Hydrostatic uplift resistance is needed etc.

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Serviceability criteria

Raft foundation

• Bossinesq’s Theory

• Construction joints for raft • Large differential settlement

Design stresses in raft foundation

SETTLEMENTS OF FOUNDATIONS

NO SETTLEMENT * TOTAL SETTLEMENT DIFFERENTIAL SETTLEMENT

Uniform settlement is usually of little consequence in a building, but differential settlement can cause severe structural damage

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Types of Mat Foundations

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To Design Mat Foundation:

• Determine the capacity of the foundation

• Determine the settlement of foundation

• Determine the differential settlement

• Determine the stress distribution beneath the foundation

• Design the structural component of the mat foundation using the stress distribution obtain from 4.

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2). Settlement of foundation

The settlement tends to be controlled via the following:

Use of a larger foundation to produce lower soil contact pressures.

Displaced volume of soil (flotation effect); theoretically if the weight of excavation equals the combined weight of the structure and mat, the system "floats" in the soil mass and no settlement occurs.

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Bridging effects attributable to

• a. Mat rigidity.

• b. Contribution of superstructure rigidity to the mat.

By IS Code – 2950 (Part-1)

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Foundation type Expected maximum settlement, mm

Expected differential settlement, mm

Spread 25 20

Mat 50 20

Construction: Unrestricted Site

Bench and/or Angle of Repose Must have perimeter clearance Considerations

Bank Erosion Water Diversion Safety Storage of Backfill (& cost)

Most likely - least expensive

Benched Excavation

Solder Beam & Lagging

Sheet Pile Options

Slurry Wall

Steps Layout

Excavate the soil

Interject Slurry to

prevent Collapse as

Excavation Continues

Install Reinforcing

Place Concrete

(replaces the slurry mix)

Tieback Installation

Rotary Drill Hole

Insert & Grout Tendons

Tendons Stressed & Anchored

Bracing

Crosslot

Rackers

Tiebacks

Bank Requiring a Retention System

Retention System Depends On:

Proximity to Buildings

Type of Soil

Water Table Level

Temporary or Permanent

Contractor Preference

Cost - KEY Consideration

REINFORCEMENT DETAILS OF MAT FOUNDATION

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MAT FOUNDATION WITH REINFORCED BARS

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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

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.

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

Pile foundation

• Raft unstable with increasing height

• Transfer load to ground with adequate factor of safety

• Differential settlement • Pile positioning

• Pile geometry

Design stress on pile foundation

CHOICE OF PILE • Availability • Location & type of structure • Ground Condition (soil type) • Cost • Durability

TYPES OF PILE CONSTRUCTION

Displacement Piles

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

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

West’s Shell Pile

Franki Pile (Driven Cast in situ / Driven cased Pile)

TYPES OF DISPLACEMENT PILES:

• Totally Preformed Displacement Piles • (precast concrete or steel pile)

• Driven & Cast-In-Place Displacement Pile

• Helical Cast-In-Place Displacement Piles

Totally Preformed Displacement Piles

- Precast Concrete or Steel Pile

Driven & Cast-In-Place Displacement Pile

Uncased

Cased

TYPES OF PILES

• Concrete Piles • Cast-In-Place Concrete Piles

• Precast Concrete Piles

• Drilled Shafts

• Steel Piles • H-Piles

• Cylindrical

• Tapered

• Timber Piles

• Composite Piles

CAST IN PLACE CONCRETE PILES

Formed by driving a cylindrical steel shell into the

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

It’s purpose is to open a hole in a ground and keep it open to facilitate

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

Advantages of Cast-In-Place

Can sustain hard driving

Resistant to marine organism

Easily inspected

Length can be changed easily

Easy to handle and ship

PRECAST CONCRETE PILES

• Usually have square/circular/octagonal cross sections.

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

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

• It has higher capacity than timber piles.

STEEL PILES

• It comes in various shapes & sizes

• Steel H-Piles are rolled steel sections

• Steel pipe piles are seamless pipes that can be welded to yield lengths up to 70m.

• They are usually driven with open ends into the soil.

• A conical tip is used where the piles have to penetrate boulders & rocks.

• However it needs to be treated before embedded in corrosive environment.

Helical Cast-In-Place Displacement Piles

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

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

• Dropping Weight or Drop Hammers • commonly used method of insertion of displacement piles

• Diesel Hammers • Most suitable to drive pile in non cohesive granular soil

• Vibratory Hammers or vibratory method of pile driving • very effective in driving piles through non cohesive granular soil • excites the soil grains adjacent to the pile making the soil almost free flowing • result in the settlement of nearby buildings.

• Jacking Method Of Insertion

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 f the pile thus reducing any excess stresses along the length of the tube during insertion.

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.

NON DISPLACEMENT PILES

• Small Diameter Cast-In-Place

• Large Diameter Cast-In-Place

• Partially Preformed Piles

• Grout or Concrete Intruded Piles

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.

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

Piled Raft Foundation

Behavior of raft

Pile Foundation

Combined Pile Raft Foundation (CPRF)

• Load transfer • skin friction

• end bearing

• contact pressures of the raft foundation

• The piles are used up to their ultimate bearing capacity • higher than the permissible design value for a comparable single pile

• Qualified understanding of the soil-structure interactions.

CPRF

Combined pile raft action

Case study

Area 5400sqm Height 76.8m 3 basements

Raft: 900sqm & 2.5m ht 32 piles 1.2m dia 10.5 to 16.5m