Foundation

Introduction Types of Soils and Characteristics Construction of Foundation Types of Foundations
Foundations
Rakesh J. Pillai
National Institute of Technology Warangal
January 29, 2015
Rakesh J. Pillai NITW
Foundations

Outline
1 Introduction
Foundation
Loads on Foundations
Settlements of Foundations
2 Types of Soils and Characteristics
3 Construction of Foundation
Foundation Construction
4 Types of Foundations
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Foundation
Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Foundation
Introduction
Foundation
Function of a foundation is to transfer the structural loads
from a building safely into the ground
Foundations should rest on soil with suﬃcient strength and
competent to carry the massive loads coming from buildings
A variety of soils, rocks and water conditions may be
encountered below the ground surface; hence foundation
design is a highly specialized ﬁeld of civil engineering
Foundations

Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Dead load
Live load
Wind load
Earthquake load
Uplift pressures (eg. foundations on expansive soils and
marine foundations)
Foundations

Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Deformations of the foundation soil is called settlement
Should be with in permissible limits
Two types of settlements:
Uniform settlement - All parts of the building settles uniformly
Diﬀerential settlement - Some portion settles more than other
portion
Figure : (a) No settlement, (b) Uniform settlement, (c) DiﬀerentialRakesh J. Pillai NITW
Foundations

Types of Soils and characteristics
Loads from buildings are transfered through foundation to the
soil underground
Soils usually classiﬁed based on the particle size
Boulders and cobbles (large size particles)
Gravel - coarse grained particles with size > 5 mm
Sand - particle size varies from 5mm - 0.075mm (load transfer
by friction)
Silt - particle size varies from 0.075mm - 0.002mm
(intermediate behaviour of sand and clays)
Clay - particle size < 0.002 mm (load transfer by cohesion)
Peat - organic, not suitable for foundations
Foundations

Sand and Clays
Sand
Sand is cohensionless and the
resistance is oﬀered by the internal
friction between the particles
Clay
In the case of clay, cohesion between
the particles oﬀers the resistance
Foundations

Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Construction of Foundation
3 important steps before construction of foundations
Excavation: It is an important step in construction of
foundation; should be excavated to a level where suﬃcient
bearing capacity of soil is available. A variety of machines are
used for excavation (Dozers, Backhoes)
The sides of excavation to be protected from caving
Benching
Sheeting (solder beams, slurry walls, sheet piles etc.)
Bracing (cross-slot, rakers, tie backs etc.)
De-watering using well-points and sumps
Each of these steps explained in following slides
Foundations

Excavation
Machines for excavation - dozers,
backhoe
Machines for taking out soil -
bucket loaders, scrapers
For hard strata - Power shovels,
tractor mounted rippers,
pneumatic hammers
For harder strata - drop balls,
hydraulic splitters, blasting
(a) Dozer and (b) Backhoe
Foundations

Protection from Caving
Benched Excavation
Used when there is no
restriction or when plenty of
space is available
Slopes provided less than angle
of repose and benches are
provided in between, for
greater depths
Less expensive and commonly
used
Foundations

Sheeting - Solder beams and lagging
Foundations

Sheeting - Sheet piles (long
structural section with
vertical inter-locking system
that creates a continuous
wall)
Made of diﬀerent materials
(steel is commonly used)
Available in diﬀerent cross
sections (shape)
Foundations

Bracing - Diﬀerent types
Crosslot bracing
Rakers
Tiebacks
Foundations

Tieback Installation
A Rotary drill hole
B Insert and grount tendons
C Tendons stressed and
anchored
Foundations

Dewatering
Process of removing water and/or lowering the water table
within the construction site
Purpose of dewatering is to provide a dry working platform
If water table is above the working platform there are three
options:
Keep water out
Let water in and then remove it using a pump system
Combination of the above two
Foundations

Dewatering
Watertight Barrier Walls
Barrier must reach an
impervious strata to keep
the water out
Diﬀerent types
Slurry walls
Sheeting (sheet piles are
widely used)
Barrier should resist the
hydrostatic pressure
Foundations

Foundation Types
Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Foundation Types
Type of Foundations
Two types
Shallow foundations
Deep foundations
Based on whether the load transfer is at deeper depths or
shallower depths
The depth of load transfer depends on:
Soil strength
Ground water conditions
Foundation loads
Construction methods
Impact on adjacent property
Foundations

Shallow Foundation
Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Shallow Foundation
Shallow Foundations
Requirements
Suitable soil bearing capacity
Undisturbed soil or engineered ﬁll
Basic types or conﬁgurations
Column footings or isolated footings (spread footings and
stepped footings)
Wall or strip footings
Other types
Column footings with tie beams
Combined footing
Raft (or Mat) footing
Foundations

Shallow Foundation
Shallow Foundations
Strip footing is continuous and
takes load directly from the
load bearing walls
Column footings or isolated
footings support and take load
from a single column
sometimes the c/s area is
increased with depth to
form a spread footing
sometimes the c/s area is
increased in steps to form
stepped footing
Combined strip and isolated footing
Foundations

Shallow Foundation
Shallow Foundations
Combined footing is when
two columns are provided on
the same footing (usually
provided when the spacing
between the columns are
less)
In the case of raft or mat
foundation, a single
foundation (in the form of
mat) is provided for all the
columns of the building
Mat foundation
Foundations

Deep Foundation
Outline
1 Introduction
Foundation
Foundation Types
Shallow Foundation
Deep Foundation
Foundations

Deep Foundation
Deep Foundation
Deep foundations transfer the building load deep in to the earth
Piles, Cassions, Well foundations
Foundations

Deep Foundation
Deep Foundation
Diﬀerent Types of Piles
Based on Load Transfer
Friction piles - load transferred by the frictional resistance between
the pile and the soil
End bearing piles - load transferred to a hard strata through the end
of pile (point loading)
Based on construction method (for concrete piles)
Precast Driven piles - piles are casted in a yard, brought to the site
and driven in to the soil (by hammer blows or other methods)
Bored cast-in situ piles - a bore (hole) of required diameter and
depth is dug and the reinforcement and concrete is placed to form
the pile
Driven cast-insitu piles - a casing is driven initially and the
reinforcement and concrete is placed after taking out soil inside the
casing
Foundations

Deep Foundation
Deep Foundation
Pile material
Steel (H - piles or steel pipe piles)
Concrete (cast-in situ or precast)
Timber
Composite
Foundations

Deep Foundation
Deep Foundation
Precast steel (H piles) and concrete piles
Foundations

Deep Foundation
Thank You !!!
Foundations

Foundation

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