For full course visit our website : https://www.machenlink.com/course/foundation-engineering/ Description: This test (IS: 2131 – 1981) is performed in a clean hole, 100 to 150 mm in diameter. A casing or drilling mud is used to support the sides of the hole. This test is most commonly used for cohesionless soil which can not be easily sampled. Useful for determining the relative density and the angle of shear resistance. It can also be used to determine the unconfined compressive strength of cohesive soil. The test shall be made,… At every change in stratum At intervals not more than 1.5 m If the number of blows for 150mm exceeds 50 it is taken as a refusal and the test is discontinuous For full course visit our website : https://www.machenlink.com/course/foundation-engineering/ Follow #MachenLink Facebook: https://www.facebook.com/machenLink/ Linkedin: https://www.linkedin.com/company/machenlink/ Twitter: https://twitter.com/MachenLink

1. FOUNDATION
ENGINEERING
Standard
Penetration
Test

2. MachenLink
STANDARD PENETRATION TEST (SPT)
• This test (IS : 2131 – 1981) is performed in clean hole, 100 to 150 mm in
diameter.
• A casing or drilling mud is used to support the sides of the hole.
63.5 𝑘𝑔 Drop
hammer repeatedly
falling 75 𝑐𝑚
Anvil
Drill rod
Split – barrel (drive)
sampler [thick hollow
tube:
O.D.= 50.8 𝑚𝑚
I.D. = 35 𝑚𝑚
L= 456 to 762 mm
• This test is most commonly used for cohesionless soil which can
not be easily sampled.
• Useful for determining the relative density and the angle of shear
resistance.
• It can also be used to determine the unconfined compressive
strength of cohesive soil.
• Test shall be made,…
• At every change in stratum
• At intervals not more than 1.5 m
30 blows per
minute
Whichever is less

3. MachenLink
STANDARD PENETRATION TEST (SPT)
63.5 𝑘𝑔 Drop
hammer repeatedly
falling 75 𝑐𝑚
Anvil
150 𝑚𝑚
Drill rod
Split – barrel (drive)
sampler [thick hollow
tube:
O.D.= 50.8 𝑚𝑚
I.D. = 35 𝑚𝑚
L= 456 to 762 mm
First Increment
30 blows per
minute
• This test (IS : 2131 – 1981) is performed in clean hole, 100 to 150 mm in
diameter.
• A casing or drilling mud is used to support the sides of the hole.
• This test is most commonly used for cohesionless soil which can
not be easily sampled.
• Useful for determining the relative density and the angle of shear
resistance.
• It can also be used to determine the unconfined compressive
strength of cohesive soil.
• Test shall be made,…
• At every change in stratum
• At intervals not more than 1.5 m
Whichever is less

4. MachenLink
STANDARD PENETRATION TEST (SPT)
150 𝑚𝑚
Split – barrel (drive)
sampler [thick hollow
tube:
O.D.= 50.8 𝑚𝑚
I.D. = 35 𝑚𝑚
L= 456 to 762 mm
150 𝑚𝑚
First Increment
Second Increment
150 𝑚𝑚 Third Increment
SPT (𝑁𝑜) = the number of blows required for 300mm penetration
If the number of blows for 150mm exceeds 50 it is taken as
refusal and the test is discontinuous
• This test (IS : 2131 – 1981) is performed in clean hole, 100 to 150 mm in
diameter.
• A casing or drilling mud is used to support the sides of the hole.
• This test is most commonly used for cohesionless soil which can
not be easily sampled.
• Useful for determining the relative density and the angle of shear
resistance.
• It can also be used to determine the unconfined compressive
strength of cohesive soil.
• Test shall be made,…
• At every change in stratum
• At intervals not more than 1.5 m
Whichever is less

5. MachenLink
SPT CORRECTIONS
Overburden pressure correction
Let 𝑁𝑜 is observed value of SPT for 1st correction factor and 𝑁𝑐
corrected value for overburden pressure then,
𝑵 𝒄 = 𝑵 𝒐 ×
𝟑𝟓𝟎
𝝈′ + 𝟕𝟎
𝜎′
≯ 280 𝑘𝑁/𝑚²
𝜎′ = effective overburden pressure at the test level
If 𝜎′
> 280 𝑘𝑁/𝑚², then overburden pressure correction is not required.
The ratio 𝑁𝑐 𝑁𝑜 should lie between 0.45 & 2.
𝑁𝑐 𝑁𝑜 > 2If,
𝑁𝑐 should be divided by 2 to obtain the design value used in finding
the bearing capacity of soil.
In granular soil, overburden pressure affects the penetration resistance.
Higher the confining pressure, higher will be penetration resistance.
Cohesionless soils of
same relative density
Penetration number
increase with depth
as confining pressure
increase.
𝑁𝑜 - Overestimated
𝑁𝑜 - Underestimated

6. MachenLink
Water table correction/ fine correction/ dilatancy
• If water table is present at or above the test level then water table correction is required. If 𝑤 𝑇 is below the test
level then it is not required.
The corrected value for overburden pressure is further corrected for presence of water table,
• The pore water pressure is developed due to presence of water table
• In fine soil during dynamic action of hammer the pore water resistance is developed.
SPT CORRECTIONS
𝑵 𝒘 = 𝟏𝟓 +
𝟏
𝟐
𝑵 𝒄 − 𝟏𝟓
The correction is required when 𝑁𝑐 is greater than 15.
If 𝑁𝑐 is less than 15, then water table correction is not required.
Let 𝑁𝑐 be the corrected value for overburden pressure and 𝑁 𝑤 be the corrected value for water table, then

7. MachenLink
Penetration Resistance and empirical correlation for Cohesionless Soil
Penetration
resistance N (Blows)
Approx. 𝜙 (degrees) Density index % Description Approx. moist
density 𝑡/𝑚3
− 25 − 30 0 Very loose 1.12 − 1.6
4 27 − 32 15 Loose 1.44 − 1.84
10 30 − 35 35 Medium 1.76 − 2.08
30 35 − 40 65 Dense 1.76 − 2.24
50 38 − 43 85 Very dense 2.08 − 2.4
− 100
CORRELATION OF SPT (N) WITH ENGINEERING PROPERTIES
The value of SPT number depends upon,…
Relative density → For cohesionless soil
Unconfined compressive strength → For cohesive soil

8. MachenLink
CORRELATION OF SPT (N) WITH ENGINEERING PROPERTIES
Penetration resistance N
(blows)
Unconfined compressive
strength 𝑡/𝑚2
Saturated density 𝑡/𝑚3 Consistency
0 0 Very soft
2 2.5 1.6 − 1.92 Soft
4 5 1.76 − 2.08 Medium
8 10 Stiff
16 20 1.92 − 2.24 Very stiff
32 40 Hard
Penetration Resistance and empirical correlation for Cohesive Soils