Foundation for High Rise
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Transcript of Foundation for High Rise
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