A very Good Presentation on Standard Penetration Test of Soil Mechanics.

1. PRESENTED BY:
Saif Khan
Saif Ul Islam
Saleem Sajjad Naqvi
Sana Fatima
Sana Fatima Ali
10-CES-56
10-CES-57
10-CES-58
10-CES-59
10-CES-60
Geotechnical Engineering
Standard Penetration Test
JAMIA MILLIA ISLAMIA
NEW DELHI-25

2. INTRODUCTION
Especially for
Most commonly
cohesion less soils,
used In-situ test
which cant be easily
sampled

3. USEFUL IN
FINDING
OUT

4. INSTRUMENTS
1. DRILLING EQUIPMENT FOR BOREHOLES:
Any drilling equipment is
acceptable that provides
a reasonably clean hole,
which is at least 5 mm
larger than the sampler or
sampling rods, and less
than 170 mm diameter.

5. INSTRUMENTS
2. SPLIT – SPOON SAMPLER
It is a sampler for obtaining a
disturbed sample of soil and
consists ofoDriving shoe : Made of tool-stee
about 75 mm long
oSteel Tube : 450 mm long, split
longitudinally in two halves
oCoupling : 150 mm long,
provided at the top
oCheck Valve
o4 Venting Ports : 10 mm
diameter

6. INSTRUMENTS
3. DRIVE – WEIGHT ASSEMBLY
• Hammer of 63.5 kg
• A driving Head (Anvil)
• A guide permitting a free fall of
0.76 m and over lift capability
of at least 100 mm.

7. INSTRUMENTS
4. CATHEAD
• Operating at approximately
100 rpm
• Equipped with suitable rope
and overhead sheave for
lifting drive-weight

8. 5) HAMMER
a) Safety Hammer
•
Closed system
•
Delivers approximately 60%
of the maximum free fall
energy
•
Highly variable energy
transfer

9. b) Donut Hammer
• Open system
• Delivers approximately
45% of the maximum
free fall energy
• Highly variable energy
transfer

10. c) Automatic Hammer
• Safest system
• Delivers approximately
95 - 100% of the
maximum free fall
energy
• Consistent and effective
energy transfer
• Increased production

11. PROCEDURE
1.DRILLING OF BOREHOLE
New Picture Effects
• Drill the borehole to the desired sampling
depth and clean out all disturbed material.
• The equipment used shall provide a clean
borehole, 100 to 150 mm in diameter, for
insertion of the sampler to ensure that the
penetration test is performed on undisturbed
soil.
• Casing shall be used when drilling in sand,
soft clay or other soils in which the sides of
borehole are likely to cave in.

12. PROCEDURE
2.Driving the Casing
• Where casing is used, it shall not be driven
below the level at which the test is made or
soil sample is taken.
• In the case of cohesion less soils which
cannot stand without casing, the
advancement of the casing pipe should be
such that it does not disturb the soil to be
tested or sampled; the casing shall
preferably be advanced by slowly turning
the casing rather than by driving, as the
vibration caused by driving may alter the
density of such deposits immediately below
the bottom of the borehole.

13. PROCEDURE
3. ASSEMBLING EQUIPMENT
• Attach the split-spoon sampler to the drill rod
and lower into the hole until it is sitting on the
undisturbed material.
• Attach the drive weight assembly.
• Lift the 63.5 kg hammer approximately 0.76 m
and allow it to fall on the anvil delivering one
seating blow.
• Mark the drill rod in 3 successive .15 m
increments to observe penetration.

14. PROCEDURE
New Picture Effects

15. PROCEDURE
4. PENETRATION TESTING
New Picture Effects
• Raise and drop the hammer 0.76 m successively
by means of the rope and cathead, using no
more than two and one forth wraps around the
cathead.
• The hammer should be operated between 40
and 60 blows per minute and should drop freely.
• Record the number of blows for each .15 m of
the penetration.
• The first 0.15 m increment is the "seating" drive.

16. PROCEDURE
• The sum of the blows for second and third
increment of 0.15 m penetration is termed
"penetration resistance or "N-value".
• If the split spoon sampler is driven less than 45
cm (total), then the penetration resistance shall
be for the last 30 cm of penetration (if less than
30 cm is penetrated, the logs should state the
number of blows and the depth penetrated).
• If the no. of blows for 15cm drive exceeds 50, it
is taken as a refusal and the test is discontinued.
• Tests shall be made at every change in stratum
or at intervals of not more than l-5 m whichever
is less. Tests may be made at lesser intervals if
specified or considered necessary.

17. PROCEDURE
• The intervals be increased to 3 m if in between
vane shear test is performed.( as per IS:21311963) .
• The entire sampler may sometimes sink under
its own weight when very soft sub-soil stratum
is encountered.
• Under such conditions, it may not be necessary
to give any blow to the split spoon sampler and
SPT value should be indicated as zero.

19. PROCEDURE
Ne4. Handling Sample
w Picture Effects
• Bring the sampler to the surface and open it.
Remove any obvious contamination from the
ends or sides and drain excess water. Carefully
scrape or slice along one side to expose fresh
material and any stratification.
• Record the length, composition, colour,
stratification and condition of sample.
• Remove sample and wrap it or seal in a plastic
bag to retain moisture. If the sample can be
removed relatively intact, wrap it in several
layers of plastic and seal ends with tape.

20. CORRECTIONS
DILATANCY CORRECTION
• Silty fine sands and fine sand below the water
table develop pore pressure which is not easily
dissipated.
• Pore pressure increases the resistance of the soil
thus, Penetration Number (N) also increases
• This correction is applied when observed value
of N exceeds 15

21. CORRECTIONS
DILATANCY CORRECTION
• Terzaghi and Peck (1967) recommended the
following correction-

22. CORRECTIONS
OVERBURDEN PRESSURE CORRECTION
• In granular soils, overburden pressure affects the
penetration resistance
• If two soils, having same relative density but
different confining pressures are tested, the one
with a higher confining pressure gives a higher
penetration number as the confining pressure in
cohesion less soils increases with the depth, the
penetration number for soils at shallow depths is
underestimated and that at greater depths is
overestimated.
• For uniformity, the N- values obtained from field
tests under different effective overburden
pressures are corrected to a standard effective
overburden pressure.

23. CORRECTIONS
1. GIBBS AND HOLTZ’ CORRECTION (1957)

24. CORRECTIONS APPLIED
2. PECK, HANSEN AND THORNBURN’S CORRECTION

25. CORRECTIONS APPLIED
3. PECK AND BAZARAA’S CORRECTION
• One of the most commonly used corrections
• According to them,

26. FACTORS
COMMENTS
Attitude of operators
Blow counts for the same soil using the same rig can
vary, depending on who is operating the rig, and
perhaps the mood of operator and time of drilling.
Overdrive sampler
Higher blow counts usually result from an overdriven
sampler.
Sampler plugged by gravel
Higher blow counts result when gravel plugs the
sampler, resistance of loose sand could be highly
overestimated.
Plugged casing
High N-values may be recorded for loose sand when
sampling below groundwater table. Hydrostatic
pressure can cause sand to rise within the casing.

27. FACTORS
COMMENTS
Inadequate cleaning of the SPT is only partially made in original soil. Sludge may be
borehole
trapped in the sampler and compressed as the sampler
is driven, increasing the blow count (This may even
prevent sample recovery.)
Not seating the sampler
spoon on undisturbed
material
Incorrect N-values obtained.
Driving of the sample spoon
above the bottom of the
casing
N-values are increased in sands and reduced in
cohesive soils.
Failure to maintain sufficient The water table in the borehole must be at least equal
hydrostatic head in boring
to the piezometric level in the sand, otherwise the sand
at the bottom of the borehole may be transformed into
a loose state thereby decreasing the blow counts

28. FACTORS
COMMENTS
Overwashing ahead of
casing
Low blow count may result for dense sand since
overwashing loosens sand.
Drilling method
Drilling technique (e.g., cased holes vs. mud
stabilized holes) may result in different N-values for
the same soil.
Free fall of the drive weight
is not attained
Using more than 1-1/2 turns of rope around the
drum and or using wire cable will restrict the fall of
the drive weight.
Not using correct weight
Driller frequently supplies drive hammers with
weights varying from the standard by as much as 10
lbs.

29. FACTORS
COMMENTS
Weight does not strike the
drive cap concentrically
Impact energy is reduced, increasing N-values.
Not using a guide rod
Incorrect N-value obtained.
Not using a good tip on the
sampling spoon
If the tip is damaged and reduces the opening or
increases the end area the N-value can be increased.
Use of drill rods heavier than
standard
With heavier rods more energy is absorbed by the
rods causing
an increase in the blow count.

30. CORRELATIONS BETWEEN SPT AND SOIL PROPERTIES
- Relative Density
- Effective Stress Friction Angle
- Unconfined Compressive Strength
*Some correlations require the raw N-values whereas others use the
corrected N-values.

31. Relative Density

32. Unconfined Compressive Strength Of Cohesive Soils

35. ADVANTAGES
• Relatively quick and simple to perform.
• Provides a representative soil sample.
• Provides useful index of relative strength and
compressibility of the soil.
• Able to penetrate dense layers, gravel, and fill.
• Numerous case histories of soil liquefaction during past
earthquakes are available with SPT N-values. The method
based on this history can reflect actual soil behaviour
during earthquakes, which cannot be simulated in the
laboratory.

36. • The SPT is an in situ test that reflects soil density,
soil fabric, stress and strain history effects, and
horizontal effective stress, all of which are
known to influence the liquefaction resistance
but are difficult to obtain with undisturbed
samples.
The SPT equipment is rugged, and the test can be
performed in a wide range of soil conditions.
There are numerous correlations for predicting
engineering properties with a good degree of
confidence.

37. DISADVANTAGES
• The SPT does not typically provide continuous data,
therefore important data such as weak seams may be
missed.
• Limited applicability to cohesive soils, gravels, cobbles
boulders.
• Somewhat slower than other sample methods due to
sample retrieval.
• In addition to overburden pressure and relative density the
SPT N-value is also a function of soil type, particle size, and
age and stress history of the deposit

38. • Due to considerable differences in apparatus and procedure,
significant variability of measured penetration resistance can
occur. The basic problems to consider are change in effective
stress at the bottom of the borehole, dynamic energy
reaching the sampler, sampler design, interval of impact,
penetration resistance count.
• Samples that are obtained from the SPT are disturbed.
• The greatest disadvantage to SPTs is the lack of reproducibility
of the test results
• Drilling disturbance, mechanical variability, and operator
variability all can cause a significant variation in test results.
• Another disadvantage to SPTs is that progress is slower than
other in place tests because of incremental drilling, testing,
and sample retrieval, and SPTs may be more expensive than
other in place tests.

39. PRECAUTIONS
• The drill rods should be of standard specification and should not be
in bent condition.
• The split spoon sampler must be in good condition and the cutting
shoe must be free from wear and tear.
• The drop hammer must be of the right weight and the fall should be
free, frictionless and vertical.
• The height of fall must be exactly 750 mm. Any change from this
will seriously affect the N value.

40. • The bottom of the borehole must be properly cleaned
before the test is carried out. If this is not done, the test
gets carried out in the loose, disturbed soil and not in the
undisturbed soil.
• When a casing is used in borehole, it should be ensured
that the casing is driven just short of the level at which
the SPT is to be carried out. Otherwise, the test gets
carried out in a soil plug enclosed at the bottom of the
casing.
• When the test is carried out in a sandy soil below the
water table, it must be ensured that the water level in the
borehole is always maintained slightly above the ground
water level. If the water level in the borehole is lower
than the ground water level, ‘quick' condition may
develop in the soil and very low N values may be
recorded.

41. Thank You