SUPREME KNOWLEDGE FOUNDATION
GROUP OF INSTITUTIONS
MANKUNDU, HOOGHLY
RECENT TRENDS IN CIVIL ENGINEERING PRACTICES
– A GEOTECHNICAL OVERVIEW
25th September 2014
Suvendu Dey
Chief Engineer (Civil)
M. N. Dastur & Company (P) Ltd., Kolkata
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOIL INVESTIGATION
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
WHY INVESTIGATE ?
Bearing capacities may be better than anticipated and a different
foundation design could have saved a few lakhs of rupees. Often, a
thorough soil investigation may show that moving a unit just a few
metres on the site can avoid faulty underlying material.
Bearing capacity and settlement potential of the
soil needs to be ascertained to determine whether
the stability of foundations can be obtained. This is
required because foundation failures in structures
are practically irreparable.
A client would especially want to know what types of foundations and
other construction details are likely to be required so that he can
figure his cost to build. The client would also like to know the
additional cost for land development, if any, due to any problem or
condition of the sub-soil.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
MAJOR COMPONENTS OF SOIL INVESTIGATION
For an industrial plant, the field work for a
typical soil investigation may consist of the
following major components :
• Boreholes/Drillholes
• Standard Penetration tests in boreholes
• Trial Pits
• Plate Load Tests – Routine/Cyclic
• Block Vibration Tests
• Collecting samples of soil/rock/water
• Static (Dutch) Cone Penetration Tests
• Dynamic Cone Penetration Tests
• Electrical Resistivity Tests
• Pressuremeter Tests
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOME RECENT ADVANCEMENTS
Although the testing methodology remains
largely unchanged, huge advancement has been
brought about in equipment and machinery,
leading to more efficiency and accuracy as well
as saving in time.
Some traditional tests have been replaced by
state-of-the-art testing methods that are more
scientific and universally acceptable.
• Downhole and crosshole seismic tests
• Thermal Resistivity Tests
• Mackintosh Probe
• Hand/Pocket Penetrometers
• Piezocones
• Vibrating Wire Piezometers
• Vacuum sampling of water/soil-water solutions
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Piezocone
Mackintosh Probe
Pocket Penetrometer
Suvendu Dey
VW Piezometer
SKFGI, MANKUNDU
25.09.2014
FOUNDATIONS
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
TYPES OF FOUNDATIONS
Deep Foundation
Shallow Foundation
Resting on soil at a shallow level
with adequate bearing capacity
Piles
Any foundation system must
satisfy certain essential criteria
such as strength, settlement and
serviceability.
Hard Stratum
Taken down to deeper level to rest on
stratum with higher bearing capacity
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SHALLOW FOUNDATIONS
Foundations are designed to have an
adequate load carrying (bearing) capacity
with limited settlement. Failure of a shallow
foundation may occur in two ways :
(a) by shear failure of the soil supporting
the foundation
(b) by excessive settlement of the soil
supporting the foundation
Other design considerations include sliding, overturning, scour etc.
Foundation failure may occur due to error in design, faulty construction,
low grade materials, poor workmanship, force majeur etc.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Shallow Foundations (cont’d…)
Typical Bearing Capacity Failure
Suvendu Dey
SKFGI, MANKUNDU
Settlement Crack
25.09.2014
Shallow Foundations (cont’d…)
Typical Foundation Settlements
Overturning Failure
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
PILE FOUNDATIONS
A pile is a relatively small diameter shaft which is driven or installed into
the ground by suitable means.
Piles may be classified into different categories based on the following :
• Load Transfer Mechanism and Functional Behaviour
• Method of Installation
• Pile Material
• Orientation
• Shape
• Cross-section
• Special Types
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Pile Foundations (cont’d…)
PilePile
Classification
Types
Load
Load
Transmission
Transmission
Installation
Installation
Method
Method
Material
Material
Orientation
Orientation
Cross CrossSection
Section
Shape
Shape
Special
Special
Types
Types
End Bearing
End
Bearing
Bored
Bored
Timber
Timber
Vertical
Vertical
Cylindrical
Cylindrical
Circular
Circular
Micropiles
Micropiles
Friction
Friction
Driven
Driven
Steel
Steel
Batter/
Batter/
Raker
Tapered
Tapered
Square
Square
Suction
Suction
Under
Under
Reamed
Hexagonal/
Hexagonal/
Octagonal
Octagonal
Others
Others
Bearing&&
Bearing
Friction
Friction
Tension&&
Tension
Anchor
Anchor
Concrete
Concrete
Prestressed
Prestressed
Precast
Precast
H or
or II
Section
Section
Cast -in-situ
Cast-in-situ
Annularor
Annular
or
Pipe
Pipe
Composite
Composite
Pile Classification
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Pile Foundations (cont’d…)
Load Transfer Mechanism
Imposed Load (P)
Pile Cap
Pile
Skin Friction (Pf)
End bearing (Pb)
P = Pf + Pb
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOME RECENT ADVANCEMENTS
Use of high end software to analyse and design
foundations with precision.
Use of state-of-the art equipment, machinery
and construction techniques to ensure quality
and minimise human errors.
Use of high grade Portland/Pozzolonic cements, with or without
plasticisers and high grade reinforcing steel.
Introduction of customised courses and change
in curriculum in engineering institutions to better
equip the modern day engineer.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Piling equipment and process have seen a sea
change over the years.
The once popular conventional tripod rig is fast
giving way to high powered, mechanised,
hydraulic rotary rigs.
These rigs are powerful, versatile and speedy.
They are self erecting and can sink pile bores of
even upto 100 m. They have telescopic kellies,
are easily retractable and can be quickly ferried
from one point to the other.
They come with a host of attachments to suit the
suit conditions and piling methodology.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Driven Pile Rig
Bored Cast-in-Situ Piling Rig
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Cutting Tools
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Another fairly recent development has been the
advent of Continuous Flight Auger (CFA) piles.
The process involves one continuous operation,
without alternate lowering or raising, with the
help of an auger of the required length.
These are quick to install and are very useful in
favourable sub-soil conditions and within
reasonable depths (say 30 m).
This method is gradually gaining popularity in
our country.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
PILE TESTS
No matter how accurately soil investigation and pile design are done, the
ground never ceases to throw up surprises. Pile foundations installed at
site must be tested to verify their load carrying capacities . The most
common pile load tests that are carried out, include :
 Initial Load Tests
 Routine Load Tests
COMPRESSION
Load tests, initial or routine, are
conducted to verify the following load
carrying capacities of a pile :
TO
VERIFY
 Vertical Compression
 Vertical Tension
 Horizontal Shear
TENSION
Suvendu Dey
SKFGI, MANKUNDU
SHEAR
25.09.2014
Pile Tests (cont’d…)
Static Load Test by Maintained Load Method
Suvendu Dey
SKFGI, MANKUNDU
Kentledge for Pile Load Test
25.09.2014
SOME RECENT ADVANCEMENTS
Although carrying out load tests on piles are quite common, it has
become imperative these days to check the pile health parameters too.
The advent of non-destructive, integrity tests have
given the engineers a tool to assess parameters
such as condition of the pile shaft, soundness of pile
concrete, proper base contact, diameter and length
of pile etc.
The most common is the Sonic Integrity Test (SIT).
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
An even more recent advancement has been
the introduction of dynamic or high strain
tests on piles.
An impact force is applied axially by a pile
driving hammer resulting in a large strain
impact to the top of the pile. The test method
is used to provide data on strain or force and
acceleration, velocity or displacement of a
pile under impact force.
The data are used to estimate the bearing
capacity and integrity of a pile as well as
hammer performance, pile stresses and soil
dynamic characteristics.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOIL IMPROVEMENT
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOIL IMPROVEMENT – WHAT & WHY
Vast areas of India, particularly in the marine and alluvial environment,
consist of weak and problematic soils. These have low shear strength
and high compressibility, often accompanied with swelling properties.
Important/settlement sensitive structures cannot be placed on them
without pile foundations or appropriate ground treatment measures.
Although piles are an easy solution, the cost often
becomes prohibitive. Also, for large area loading
like material stockpiles, storage tanks etc, that can
tolerate more displacements, providing piles do
hurt the pocket of the client and the credibility of
the designer.
Thus, there is ample scope and need to utilise
alternative solutions that are technically and
economically viable. An appropriate improvement
technique not only serves the purpose, but, often
works out economical too.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOIL IMPROVEMENT – LOOKING BACK
The earliest known improvement adopted by man was to excavate a
portion of the existing loose/soft soil and refill it with compaction. With
time, he learnt to reject undesirable soil and replace it with competent
borrowed earth from nearby sources.
Over the ages, man learnt to reinforce the
ground beneath his dwelling house by driving
relatively stiffer members into the ground.
From tree trunks/logs to holes filled with
stones, and later, inserting metal pipes/rods
into the ground, man has used them all! He
even learnt to apply different techniques to suit
different sub-soil conditions etc.
Today, man has at his disposal state-of-the-art methods for shallow and
deep soil improvement along with natural or synthetic fibres to reinforce
the ground.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
SOME RECENT ADVANCEMENTS
Soil Nailing is an in-situ soil reinforcement technique that is used to
stabilise natural slopes, cut or excavation, walls in stiff cliffs, granular
soils and also soft rocks.
The nails are installed perpendicular to the
surface of the slope in such a way as to
create a stable mass of soil. This process
creates a single block of earth that is stable
and able to hold back the soil behind.
Soil nailing works in tension as well as with
bending and shearing forces. Lateral earth
forces are picked up in both tension and
bending stress in the nail. Generally, the soil
nails increase the bonding of the soils
through their ability to carry tensile loads.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Rapid Impact Compaction (RIC), also known as Dynamic Compaction,
imparts energy by dropping a 5.0 ton weight from a height of about 1 m
onto a foot. Energy is delivered at a rate of 35 to 65 blows per minute.
The foot, measuring about 1.5 m in
diameter, is maintained in contact with the
ground to allow efficient and safe transfer of
energy.
Potential applications for RIC include
compaction of loose soils (cohesionless and
semi-cohesive) to improve bearing capacity
and reduce settlements.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Geosynthetics constitute a group of fabrics made from synthetic
polymers such as polypropylene, polyester, polyethylene, polyamide and
PVC, or natural fibres including cotton, jute, coir and bamboo. They find
wide application in separation, reinforcement, drainage and filtration
To be effective in reinforcement of soil,
sufficient deformation has to be allowed
so as to enable the tensile strength of
the fabric to come into play. This makes
them particularly suitable in soft clay
deposits that are by nature susceptible
to large deformations.
These days, the major application areas
of geosynthetics are roads, railways,
embankments in soft soils, drainage,
retaining walls, erosion control etc.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Compaction Grouting involves injection of thick consistency soil-cement
grout, under pressure, into the soil mass, consolidating, and thereby
densifying the surrounding soils in-place by pressure densification.
Improved compaction of displaced soils and
greater uniformity of the treated soil mass is
achieved. A secondary benefit is that the
grout columns add strength along the
vertical axis, as grout compressive strengths
exceed those of the surrounding soils.
Chemical Grouting is done for soils with
medium to low permeability (k<10-4 m/sec).
Sodium silicates are commonly used, which
reacts to form sodium carbonate and silica,
that remain in the voids as grout.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Vibro-compaction is a deep compaction
ground treatment technique for in-situ
densification of granular soils by means of a
vibrating probe, or vibroflot.
The vibroflot consists of a vibrator,
connected to an upper follow tube. The
vibrator houses an electric motor in the
upper part, to drive an eccentric weight in
the lower compartment. Capable of
generating 1500 to 1800 rpm, the vibrator
develops a centrifugal force of 30 to 50 t,
creating vibrations in a horizontal plane.
Under the influence of vibration, loose particles are rearranged into a
more compact state, improving the engineering properties of the treated
profile. Consequently, the bearing capacity of the treated soil is
increased and the settlement potential reduces.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Stone Columns are being increasingly used for improvement of soft
ground to increase bearing capacity and reduce settlement. The
technique has been successfully applied to foundations of buildings,
embankments, storage tanks and other light/medium loaded structures.
Stone columns are essentially a
system of soil reinforcement with
additional advantage of providing
a drainage path. Hence the ground
treated by stone columns can be
improved further by preloading.
Two approaches are commonly
used, a wet top feed method and a
dry bottom feed method.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Some Recent Advancements (cont’d…)
Prefabricated Vertical Drains (PVD) with preloading is one of the most
effective means to improve bearing capacity and reduce settlements in
soft clay deposits. This method facilitates accelerated consolidation of
soft and saturated clay deposits employing a superimposed surcharge
with the help of predetermined artificial drainage paths. The basic
phenomenon involved is one of three-dimensional consolidation.
The introduction of synthetic
drains has replaced the existing
system of using sand drains and
sand wicks.
This technique is widely used
for large area loading like
material stockpiles, tanks, silos,
bunkers etc and is also known
to have been applied for
airstrips and runways.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
I have only touched the tip of the iceberg.
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014
Thank you for your time
Suvendu Dey
SKFGI, MANKUNDU
25.09.2014