1. Ingeniería

GEOTECHNICAL ENGINEERING II
MODULE – I
CHAPTER – 2
Site investigation and soil exploration
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SYLLABUS - Module I
2. Site investigation and soil exploration:
objectives - planning - reconnaissance - depth
and lateral extent of explorations -methods of
subsurface exploration - test pits - Auger borings
- rotary drilling –Types of soil samples-split
spoon samplers- Standard penetration testhand cut samples- boring log - soil profilegeophysical methods (in brief).
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
2
OBJECTIVES OF SOIL INVESTIGATION
● Determination of
– The nature of the deposits of soil
– The depth and thickness of the various soil strata and
their extent in the horizontal direction
– The location of ground water and fluctuations in GWT
– Engineering properties of the soil and rock strata by
conducting laboratory tests
– In-situ properties of soil by performing field tests
● Obtaining soil and rock samples from the various strata
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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Geotechnical
Investigation
Reconnaissance
Preliminary
Investigations
Detailed
Investigations
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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RECONNAISSANCE
● Inspection of the site and study of the topographical
f t
features
p and other relevant records.
● Studyy of maps
● Collect details about proposed constructions
● Collect
C ll t already
l d existing
i ti
d t and
data
d then
th
examine
i
f
for
soils and geological conditions
● Collect details required for economic designs
● Helps in deciding future programme of site
investigations, scope of work, methods of
exploration to be adopted, types of samples to be
taken and the laboratory testing and in
in-situ
situ testing.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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Study of Maps
● Study of maps from Survey of India or
Geological survey of India to get information
regarding faults, folds, cracks, fissures, etc.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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Folds
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Faults
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Aerial photography
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Satellite images
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
PRELIMINARY INVESTIGATIONS
● To determine the depth, thickness, extent and
composition
iti off each
h stratum
t t
att the
th site.
it
● The depth of bed rock and the ground water
table is also determined.
● Generally in the form of test pits and few borings
● Tests are conducted with cone penetrometers
and sounding rods to obtain information about
the strength and compressibility of soils.
● Geoph
Geophysical
sical methods are used
sed for locating the
boundaries of different strata.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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Detailed
Investigations
Direct
Method
¾Trial Pits
¾Trenches
¾Auger Boring
¾Shell and Auger Boring
¾Wash Boring
¾Percussion Drilling
¾Rotary Drilling
Semi-direct
methods
Indirect
methods
(Borings)
Geophysical methods
¾Seismic Method
¾
¾Electrical
Resistivity Method
Soundings or penetration tests
¾Standard Penetration Test (SPT)
¾Static Cone Penetration Test (SCPT)
¾D
¾Dynamic
i C
Cone P
Penetration
t ti T
Testt (DCPT)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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DIRECT METHOD
TEST PITS
● Usually made for supplementing other methods or for
minor structures
● Visual inspection of soil
● Personal feeling of soils
● Co
Collection
ec o o
of so
soil sa
samples
p es
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SEMI DIRECT METHODS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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AUGER BORING
● For soils with sides of the hole can remain unsupported
in dry state.
state
● Hand operated – 3 to 5 m depths
● Power driven – up to 50 m depth
HAND OPERATED AUGERS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
MACHINE
OPERATED
AUGERS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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SHELL AND AUGER BORING
● Shell used for soil with sides of
the
hole
cannot
remain
unsupported.
● B
Boring
i is
i always
l
started
t t d first
fi t with
ith
augering and the shell is used for
advancing the bore hole.
● Shell raised above the bottom of
the hole and allow it to fall freely.
p
of the drop
p cuts the
The impact
soil and pushes the soil in to the
tube.
● After filled, shell is withdrawn
and emptied.
emptied
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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WASH BORING
● For soils which auger
boring is not suitable
● For soils not mixed with
gravel and boulders
● For collecting samples,
samples
replace drill bit with
samplers
l
● Change of rate of
progress and change of
colour of wash water
indicate change in soil
strata
t t
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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PERCUSSION DRILLING
● Heavy drill bit suspended
from a drill rod or a cable
and is driven by repeated
blows
● Water is added to
facilitate the breaking of
stiff sol or rock
● Not suitable for loose
sand and is slow in
plastic clays
p
y
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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PERCUSSION
DRILLING
TOOLS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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ROTARY DRILLING
● Fast in rocks
● Drill bit fixed to the lower end
of a drill rod is rotated by
power
● Bentonite slurry
y is forced
under pressure through the
drill rod and it comes up along
the cutting soil
● Rock cores can be obtained by
using
g suitable diamond drill
bits and core barrels
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ROTARY DRILLING
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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DEPTH OF EXPLORATION
● Governed by the depth of the
influence zone which depends
on the type of structure,
intensity of loading,
loading shape and
disposition of the loaded area,
th soilil profile
the
fil and
d the
th physical
h i l
characteristics of the soil.
● The depth upto which the
stress increment due to
superimposed
loads
can
produce significant
p
g
settlement
and shear stress is known as
the “Significant
g
Depth”.
p
PRESSURE BULB
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
GUIDELINES FOR DEPTH OF EXPLORATION
Sl. No.
TYPE OF FOUNDATION
DEPTH OF EXPLORATION
((i))
Isolated Spread Footing
g or Raft
1.5 B
(ii)
Adjacent Footings with clear spacing < 2B
1.5 L
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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ADJACENT ROWS OF FOOTINGS
Sl.
No.
TYPE OF FOUNDATION
DEPTH OF
EXPLORATION
(iii) Adjacent Rows of Footings with clear spacing < 2B
Adjacent Rows of Footings with clear spacing > 2B, but < 4B
Adjacent Rows of Footings with clear spacing P 4B
45B
4.5
3B
15B
1.5
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
PILE AND WELL FOUNDATIONS
Sl. No.
TYPE OF FOUNDATION
DEPTH OF EXPLORATION
((iv))
Pile and Well Foundation
1.5 x Width of Structure from the bearing
g
level (Toe of pile or bottom of well)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ROAD CUTS
Sl. No.
(v)
TYPE OF FOUNDATION
Road Cuts
DEPTH OF EXPLORATION
Bottom width of the cut (B)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
FILLS
Sl. No.
(vi)
TYPE OF
FOUNDATION
Fills
DEPTH OF EXPLORATION
2 m below GL or height of fill (H) whichever is greater
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SOWERS AND SOWERS (1970) FORMULA
● Empirical Relationship for Multistoreyed Buildings
D = C (S)
0.7
where
D = Depth of exploration
C = Constant
= 3 for Light steel buildings
& Narrow concrete bldgs
= 6 for Heavy
Hea Steel bldgs & Wide Concrete bldgs.
bldgs
S = No. of storeys
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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Spacing of Borings
● The number and spacing of bore holes or trial pits will
depend upon the extent of the site and nature of
structures coming on it.
● For a compact building site covering an area of about
0.4 hectre, one bore hole or trial pit in each corner and
one in the centre.
● For smaller buildings,
buildings one bore hole or trial pit in the
centre.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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Sl. No. Nature of project
Spacing
1.
Highways
300 to 600 m
2.
Earth dams
30 to 60 m
3.
3
Borrow
o o p
pits
s
30 to
o 120
0m
4
4.
Multi-storey
Multi
storey buildings
15 to 30 m
5
5.
Single storey factories
30 to 90 m
m.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SAMPLES
● DISTURBED SAMPLES
– REPRESENTATIVE SAMPLES
•
•
•
•
GRAIN SIZE ANALYSIS
ATTERBER LIMITS
SPECIFIC GRAVITY
CHEMICAL ANALYSIS
– NON
NON-REPRESENTATIVE
REPRESENTATIVE SAMPLES
• Mixture of materials from various strata or some
mineral constituents lost
● UNDISTURBED SAMPLES
•
•
•
•
SHEAR STRENGTH PARAMETERS
CONSOLIDATION PARAMETERS
IN-SITU DENSITY AND WATER CONTENT
COEFFICIENT OF PERMEABILITY
● BLOCK OR CHUNK SAMPLES
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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SAMPLERS
● Based on Mode of operation
– Open Drive Samplers
• Thick wall type – Split Spoon Sampler (SPT
S
Sampler)
l )
• Thin wall type
yp – Shelby
y Tube Sampler
p
((UDS
Sampler)
– Stationary Piston Sampler
– Rotary Sampler
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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SPLIT SPOON SAMPLER
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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THIN WALLED SAMPLER
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SEALING METHODS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
PISTON SAMPLER
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
OSTERBERG PISTON SAMPLER
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ROTARY SAMPLER
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
BLOCK OR CHUNK SAMPLES
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
39
SAMPLER PARAMETERS
● Inside Clearance (CI)
– Should be between 1 to 3 %
– All
Allows for
f
elastic
l ti expansion
i
off
the soil as it enters the tube,
reduces frictional drag on the
sample from the wall of the tube.
● Outside Clearance (Co)
– The outside clearance should not
be much greater than the inside
clearance.
– This facilitates the withdrawal of
the sampler from the ground.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
41
SAMPLER PARAMETERS
● Area Ratio (Ar)
− Should be kept as low as possible.
− ≤ 20% for stiff formations and ≤10% for soft sensitive clays.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
42
University Questions
● Comment on the area ratios of the following samples:
Outer Dia (mm)
Inner Dia (mm)
(i) Split spoon sampler
50
25
(ii) Drive tube
100
90
(iii) Shelby tube
50
47
Solution :
Outer Dia
(mm)
Inner Dia
(mm)
Area Ratio
(i) Split spoon sampler
50
25
300 %
(ii) Drive tube
100
90
23.46 %
(iii) Shelby
Sh lb tube
t b
50
47
13 17 %
13.17
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
43
Rock Coring Parameters
Core Recovery =
Length of the core recovered
Total Core Run
R n Length
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
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