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2. engineering

INDIRECT METHODS
SOUNDING OR PENETRATION TESTS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
STANDARD PENETRATION TEST (SPT)
● Reference can be made to IS 2131 – 1981 for details on SPT.
● It iss a field
e d test
es to
o es
estimate
a e the
e pe
penetration
e a o resistance
es s a ce o
of so
soil.
● It consists of a split spoon sampler 50.8 mm OD, 35 mm ID,
min 600 mm long and 63.5
63 5 kg hammer freely dropped from a
height of 750 mm.
● Test is performed on a clean hole 50 mm to 150 mm diameter.
diameter
● Split spoon sampler is placed vertically in the hole, allowed to
freely settle under its own weight or with blows for first 150
mm which is called seating drive.
● The
Th number
b off blows
bl
required
i d for
f the
th nextt 300 mm penetration
t ti
into the ground is the standard penetration number N
● N value is termed as Refusal if 50 blows for any 150 mm
penetration or 100 blows for 300 mm penetration or 10
successive blows produce no advance.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
STANDARD PENETRATION TEST (SPT)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
N
Denseness
φ
0-4
Very Loose
< 28°
4 - 10
Loose
28° - 30°
10 - 30
Medium
30° - 36°
30 - 50
Dense
36° - 42°
> 50
V
Very
Dense
D
> 42°
42
CORRELATIONS OF
SPT VALUES FOR
COHESIONLESS
SOILS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
CORRELATIONS OF SPT VALUES FOR
COHESIVE SOILS
qu ≈
N
0.075
kN
N / m2
N
Consistency
qu (kN/m2)
0-2
Very soft
< 25
2–4
Soft
25 – 50
4–8
Medium
50 – 100
8 – 15
Stiff
100 – 200
15 – 30
Very Stiff
200 – 400
> 30
Hard
> 400
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
CORRECTIONS FOR SPT VALUE
● Correction for Overburden Pressure
For Cohesionless soils,
soils
⎡
2000 ⎤
N′ = ⎢0.77 log10
⎥ N ≤ 2N
q
⎣
⎦
where q is Effective overburden pressure in kN/m2.
● Correction for Dilatancy
For fine sand and silt below water table,
table
N′′ = 15 + 0.5 ( N′ − 15)
for
N′ > 15
N′′ = N′
for
N′ ≤ 15
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ADVANTAGES
● Relatively quick & simple to perform
● Equipment
E i
t & expertise
ti for
f test
t t is
i widely
id l available
il bl
p
soil sample
p
● Provides representative
● N is correlated with most properties of soil such as
friction angle,
angle undrained cohesion,
cohesion density etc.
etc
● Provides useful index
compressibility of soil
for
relative
strength
● Able to penetrate dense & stiff layers
● Results reflect soil density, stress strain behavior
● Numerous case histories available
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
&
DISADVANTAGES
● Requires the preparation of bore hole.
● Dynamic
D
i effort
ff t is
i related
l t d to
t mostly
tl static
t ti performance
f
g
g energy
gy are not uniform
● Standards regarding
● If hard stone is encountered, difficult to obtain reliable
result.
result
● Test procedure is tedious and requires heavy equipment.
● Not possible to obtain properties continuously with
depth.
depth
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
PROBLEMS
● A SPT is conducted in a sand deposit at a depth of 20 m.
Water table is at ground level. If N value is 40, find the corrected N
value. Saturated Unit weight of sand is 19 KN/m3. Take γw = 10 kN/m3.
Solution
Correction for overburden pressure
γ’ = γsat - γw = 19 – 10 = 9 kN/m3
q = Eff. Overburden pressure = γ’ D = 9 x 20 = 180 kN/m2
⎡
2000 ⎤
N′ = ⎢0.77 log10
N
⎥
q ⎦
⎣
= 0.77 x log10 (2000/180) x 40
= 0.805 x 40 = 32.2 ≅ 32 < 2 N
Correction for dilatancy
N′′ = 15 + 0.5 ( N′ − 15)
= 15 + 0.5 x ((32 – 15))
= 23.5 ≅ 23
$Corrected N Value
= 23
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
● A SPT is conducted in a sand deposit at a depth of 20 m.
Water table is at 8m below ground level. If N value is 40, find the corrected N
value. Unit weight of sand above water table is 18 KN/m3 and saturated unit
weight of sand below water table is 19 KN/m3. Take γw = 10 kN/m3.
Solution
Correction for overburden pressure
γ’ = γsat - γw = 19 – 10 = 9 kN/m3
q = Eff. Overburden pressure = γ1 D1 + γ’ D2 = 18 x 8 + 9 x 12 = 252 kN/m2
⎡
2000 ⎤
N′ = ⎢0.77 log
g10
⎥N
q
⎣
⎦
= 0.77 x log10 (2000/252) x N
= 0.693 N < 2 N
= 0.693 x 40 = 27.7 ≅ 27
Correction for dilatancy
N′′ = 15 + 0.5 ( N′ − 15)
= 15 + 0.5 x (27 – 15)
= 21
$Corrected N Value
= 21
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
● A SPT is conducted in a sand deposit at a depth of 20 m.
Water table is at 25m below ground level.
level If N value is 40,
40 find the
corrected N value. Unit weight of sand above water table is 18 KN/m3
and saturated unit weight of sand below water table is 19 KN/m3. Take
γw = 10 kN/m3.
Solution
Correction for overburden pressure
q = Eff.
Eff Overburden
O b d pressure = γ1 D1 = 18 x 20 = 360 kN/m
kN/ 2
⎡
2000 ⎤
N′ = ⎢0.77 log10
N
⎥
q ⎦
⎣
= 0.77 x log10 (2000/360) x N
= 0.573 N < 2 N
= 0.573 x 40 = 22.9 ≅ 22
There is no correction for dilatancy as the water table is below SPT depth
$Corrected N Value
= 22
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
CONE PENETRATION TEST (CPT)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
STATIC CONE PENETRATION TEST (SCPT)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
CONE PENETROMETERS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Advantages and Disadvantages
● Advantages of SCPT are
– Continuous
C ti
resistance
i t
with
ith depth
d th is
i recorded.
d d
– Static resistance is more appropriate
pp p
to determine static
properties of soil.
– Can
C be
b correlated
l t d with
ith mostt properties
ti off soil.
il
● Disadvantages
g of SCPT are
– Not very popular in India.
– If a small rock piece is encountered, resistance shown is
erratic & incorrect.
– Involves handling heavy equipment.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
LOCATION OF WATER TABLE
● Soil strength is usually reduced
below water table.
● Foundations below the water
table will be uplifted by the
water pressure.
● For soils with high permeability,
GWT is generally determined
by directly measuring to the
stabili ed water
stabilized
ater level
le el in the
bore hole after 24 to 48 hours.
● For soils with low permeability,
permeability
install a piezometer with a
porous base and a removable
top cap in the bore hole. GWT
is measured periodically until
the water level stabilizes.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
BORE LOG
● The data obtained
from bore holes,
site observations
and
laboratory
results
and
presented in a
chart form known
as Bore logs
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
BORE LOGS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SOIL PROFILE
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SOIL INVESTIGATION REPORT
● Introduction gives the scope
● Description of the proposed structure,
structure location and
geological conditions of the site
● Details
D t il off the
th field
fi ld exploration
l ti programme
● Details of the methods of explorations
● General description of the sub soil conditions
● Details of the Lab tests
● Depth of ground water table and changes in water levels
● Discussion of the results
● Recommendations about type of foundations, All. Soil
pressure or pile
il capacity,
it etc.
t
● Conclusions
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
OTHER IN-SITU TESTS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
VANE SHEAR TEST (VST)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
FIELD VANE S
SHEAR TEST
S
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
FIELD VANE SHEAR TEST
● Best suited for the determination of shear
strength of saturated cohesive soils,
especially sensitive clays, susceptible for
sampling
p g disturbances.
● Torque required to cause the failure is
measured.
D
T = πDH × τ × + 2 ×
2
D/2
∫ 2πr dr r τ
0
πD 2
πD 3
T=
H×τ+
×τ
2
6
τ=
T
⎛H D⎞
πD 2 ⎜ + ⎟
⎝2 6⎠
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
PROBLEM
● A vane used to test a deposit of soft clay, required a
torque 75 N.m.
N m The vane dimensions are D = 100 mm,
mm
and H = 200 mm. Find the value of undrained shear
strength of soil.
Solution
T
75 ×103
=
τ=
= 0.02046 N / mm 2
⎛H D⎞
⎛ 200 100 ⎞
πD 2 ⎜ + ⎟ π ×100 2 ⎜
+
⎟
6 ⎠
⎝2 6⎠
⎝ 2
= 20.46 kN/m2
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
GEOPHYSICAL METHODS
● Technique of determining subsurface materials or stratification of
soils and rocks by measuring some physical property of the
materials, viz. magnetism, density, electrical resistivity or
combination of these properties, and through correlations.
● Mechanical
M h i l Wave
W
M
Measurements
t
– Crosshole Tests (CHT)
– Downhole
D
h l Tests
T t (DHT)
– Spectral Analysis of Surface Waves
– Seismic
S i i Refraction
R f
i
– Suspension Logging
● Electromagnetic Wave Techniques
– Ground Penetrating Radar
– Electromagnetic Conductivity
– Electrical Resistivity
– Magnetometer Surveys
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Advantages and Disadvantages
● Advantages
– Non
N destructive
d t ti
– Fast and economical testing
g
– Theoretical basis for interpretation
– Applicable
A li bl to soils
il and
d rocks
k
g
● Disadvantages
– No samples or direct physical penetration
– Models assumed for interpretation
– Affected by
y cemented layers
y
or inclusions
– Results influenced by water, clay and depth
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SEISMIC REFRACTION METHOD
● General soil types & depth of different strata are judged.
● Shock or seismic waves are created by detonating small
charges of explosives or by mechanical blows on a plate
near the
th surface.
f
● Four basic wave types: Compression (P), Shear (S),
Rayleigh (R), and Love (L).
Amplitude
S R
Oscilloscope
Source
Time
P
Receiver (Geophone)
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
EQUIPMENT
Seismograph
Spectrum Analyzer
Portable Analyzer
Velocity Recorder
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SEISMIC REFRACTION METHOD
● Seismic waves have
different velocities in
different types of soil or
rock.
rock
● The waves are refracted
when they cross the
boundary
between
different types of soil.
● Radiating
g waves are
picked up and time of
travel
from
source
recorded by geophones
or seismometers.
seismometers
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
SEISMIC REFRACTION METHOD
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
DETERMINATION OF SOIL LAYERS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
Limitations of Seismic Refraction Test
● Cannot be used where a hard layer overlies a soft layer
● C
Cannott be
b used
d in
i area covered
d by
b concrete
t or asphalt
h lt
pavement which represent hard layer
● Frozen surface layer also may give results similar to the
situation of a hard layer over a soft layer.
layer
● Discontinuities such as a rock fault or earth cuts, dipping
or irregular under ground rock surface and existence of
thin layers of varying materials may cause misinterpretation of test data.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ELECTRICAL RESISTIVITY METHOD
● Based on the measurement and
recording of changes in the mean
resistivity or apparent specific
resistance of various soils.
● Significant variations in resistivity
can be detected between different
types of soils, above and below
water table,, between unfissured
rocks and soils.
● Four metal spikes are driving in ground along a straight line at equal
distances to serve as electrodes
y, flows through
g the soil between the two outer
● Current I from a battery,
electrodes, producing an electrical field within the soil.
● Potential difference E between the two inner electrodes is then
measured.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ELECTRICAL RESISTIVITY METHOD EQUIPMENTS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ELECTRICAL RESISTIVITY METHOD
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
ELECTRICAL RESISTIVITY MEASUREMENTS
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
UNIVERSITY QUESTIONS
● Briefly explain (i) Objectives of soil exploration;
(ii) Reconnaissance survey in soil exploration.
exploration
● Explain in detail Auger and Shell boring methods of site
exploration. What are its advantages and limitations?
● Explain (i) Wash Boring; (ii) Rotary Drilling.
Drilling What are its
advantages and limitations?
● List out the factors, which affect the spacing between
the bore holes.
● What is meant by significant depth of exploration? Give
guidelines, which enable the determination of the depth
of exploration.
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
●
●
●
●
●
●
●
UNIVERSITY QUESTIONS
What are the various types of samples?
Why
y undisturbed samples
p
are necessary?
y
Briefly explain the methods of obtaining undisturbed
p
samples.
Bring out the role of preservation and handling of samples
in sub-surface
sub surface exploration.
What is a bore hole? Distinguish between thin-wall and
thick-wall samplers.
samplers
Explain the working of a piston sampler with sketches.
D fi IInside
Define
id Cl
Clearance and
dO
Outside
t id Cl
Clearance as
applied to sampler. What are its significance?
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
UNIVERSITY QUESTIONS
●
●
●
●
●
●
●
What are penetration and sounding tests? Under what
you recommend these tests?
conditions do y
What is Standard Penetration Test? Explain the test setup
procedure of conducting
g the test. What are the
and the p
corrections to the observed SPT (N) value?
Discuss the merits and demerits of SPT in the sub-surface
investigation.
Briefly discuss any two methods of determining the ground
water table.
Prepare a typical soil exploration report for the construction of
a multi-storied commercial building.
Explain Seismic Refraction Method of exploration. What are its
limitations?
Explain Electrical Resistivity method of exploration. What are
it lilimitations?
its
it ti
?
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode
PLATE LOAD TEST
Dr. K. M. Kouzer, Associate Professor in Civil Engineering, GEC Kozhikode