DETERMINATION OF UNCONFINED COMPRESSIVE STRENGTH OF SOIL in Foundation Engineering INTRODUCTION TERMINOLOGY APPARATUS SOIL SPECIMEN & ITS TYPES THEORY RELEVANCE OF THE EXPERIMENT PROCEDURE VIDEO OBSERVATION DISCUSSION REMARKS

1. DETERMINATION OF
UNCONFINED COMPRESSIVE
STRENGTH OF SOIL
ASHISH NAYYAR(CO18212)
JAPTYESH SINGH(CO18229)
JOBANPREET SINGH(CO18232)
NISCHAY SINGH(CO18237)
RATTANBIR SINGH(CO18243)
SARTHAK PUNJ(CO18248)
in FOUNDATION ENGINEERING
Submitted to:
MOHAMMAD SAKIB PERWEZ KHAN SIR

2. INDEX
 INTRODUCTION
 TERMINOLOGY
 APPARATUS
 SOIL SPECIMEN & ITS TYPES
 THEORY
 RELEVANCE OF THE EXPERIMENT
 PROCEDURE
 VIDEO
 OBSERVATION
 DISCUSSION
 REMARKS

3. INTRODUCTION
[as per IS code 2720(Part X) ]
 The maximum load that can be transmitted to the subsoil by a foundation
depends upon the resistance of underlying soil to the shearing deformation
and compressibility. An axial load is applied at a constant rate of strain
without any lateral support to the soil specimen and is increased until failure
occurs.
 The compressive load per unit area required to fail the soil specimen under
such conditions is called the unconfined compressive strength of the soil.
 This test is applicable for determining strength of cohesive soils.
 In this presentation we shall demonstrate the unconfined compressive test as
per IS code 2720 Part 10.

4. TERMINOLOGY
For the purpose of this standard, the following definitions shall
apply: -
 Unconfined Compressive Strength, qu, it is the load per unit area at which
an unconfined cylindrical specimen of soil will fail in the. axial compression
test.
 If the axial compression force per unit area has not reached a maximum
value even at 20 % axial strain, qu shall be taken as the value obtained at
20% axial strain.

5. APPARATUS
1. Unconfined Compression apparatus,
(loading frame) proving ring type.
2. Proving capacity 1 KN
3. Dial gauge accuracy 0.01 mm
4. Weighing balance
5. Oven
6. Stopwatch
7. Sampling Tube
8. Split Mould (38 mm diameter, 76 mm long)
9. Sample extractor
10. Knife
11. Vernier Calliper
12. Large Mould
13. Stopwatch
14. Grease

6. APPARATUS USED
1. Unconfined Compression apparatus,
a) to apply compressive load at constant rate of strain
 Can be any of the following: (provided All these loading devices shall have sufficient capacity and strain
control.)
 Platform weighing scale equipped with a screw-jack activated yoke
 Hydraulic loading device;
 Screw jack with a proving ring; and
 Any other loading device.
b) loading frame.
c) Also includes gear for different loading.
2. proving ring type
a) with Proving capacity 1 KN
 For relatively weak soil with qu less than 100 KPa (1 kg/cm2) load shall be measurable to 1 KPa (0.1 kg/cm2).
For soils with qu equal to or greater than 100 KPa (1 kg/cm2) load shall be measurable to the nearest 5 KPa
(0.05 kg/cm2). The calibration of the proving ring shall be checked frequently, at least once a year.

7. 3. Dial gauge
 Axial deformation of the sample shall be measured with a dial gauge having a least count of 0.01 mm
and travel to permit not less than 20 percent axial strain.
4 Bearing plates
 Instrumented by clutch with help of electric motor
5. Weighing balance
 Suitable for weighing soil specimens specially. Specimens of less than 100 g shall be weighed to the nearest
0.01 g whereas specimens of 100 g or larger shall be weighed to the nearest 0.1 g.
6. Oven
 Thermostatically controlled, with interior of noncorroding material capable of maintaining the temperature at
110°C + - 5°C
7. Stopwatch
 Timing device to indicate the elapsed testing time to the nearest second may be used for establishing the rate
of strain.

8. 8. Split mould (38 mm diameter, 76 mm long)
9. Vernier Calliper
•Suitable to measure physical dimensions of the test specimen to the nearest O-1 mm.
10. Sampling Equipment
•Sampling Tube
•Sample extractor
11. Miscellaneous Equipment
•Specimen trimming and carving tools,
•remoulding apparatus,
•Large mould
•Knife
•water content cans,
•data sheets, etc, as required.
•Grease or oil

9. SOIL SPECIMEN
The soil specimen to be used for test shall be
depend on the purpose for which it is tested and
may be compacted, moulded or undisturbed.

10. SPECIMEN SIZE
 The specimen for test shall have a minimum
diameter of 38 mm and the largest particle
contained within.
 The test specimen shall be smaller than 1/8 th of
the specimen diameter.
 If after completion of test on undisturbed sample,
it is found that larger particles than permitted for
the particular specimen size tested are present.
 The height to diameter ratio shall be within 2 to
2.5.
• Measurements of height and diameter shall
be made with Vernier callipers or any other
suitable measuring device to the nearest 0.1
mm.

11. TYPES OF SPECIMEN
UNDISTURBED SPECIMEN
REMOULDED SPECIMEN
COMPACTED SPECIMEN

12. UNDISTURBED SPECIMEN
Undisturbed specimens shall be prepared from large undisturbed
samples.
 Undisturbed sample shall be prepared from the drive sampling tube.
The ejecting device shall be capable of ejecting the soil core from
the sampling tube within the same direction of travel during which
the sample entered the tube and with negligible disturbance of the
sample. Conditions at the time of removal of the sample may dictate
the direction of removal but the principle concern should be to stay
the degree disturbance negligible.
NOTES:
 Three specimens obtained by trimming and carving from
undisturbed soil samples shall be tested.
 When the sample is ejected horizontally, a curved plate
may be provided to butt against the sampling tube such
that the ejected specimen slips over it freely, This will avoid
bending of the specimen and facilitate bringing specimen
to vertical position in many cases.

13.  The specimen shall be handled carefully to stop disturbance, change in cross section or loss of
water. If any type of disturbance is likely to be caused by the ejection device the sample tube shall
be split lengthwise or be cut off in small sections, to facilitate removal of the specimen without
disturbance.
 The specimen shall be of uniform circular cross-section with ends perpendicular to the axis of the
specimen.
 Specimen of required size could also be carved from large undisturbed specimens.
Tube specimen may be tested without trimming except for squaring of ends
 Where the prevention of the possible development of applicable capillary forces is required the
specimens shall be sealed with rubber membranes, thin plastic coatings or with coating of grease
or sprayed plastic immediately after plastic immediately after preparation and through the whole
testing cycle.
 Representative sample cuttings taken from the tested specimen shall be used for determination
of water content.

14. REMOULDED SPECIMEN
The specimen could also be prepared either from a failed undisturbed specimen or from a
disturbed soil sample. Just in case of failed undisturbed specimen, the fabric shall be wrapped
during a thin rubber membrane and thoroughly worked with the fingers to assume complete
remoulding. Care shall be taken to avoid entrapped air, to get uniform density, to remould to
an equivalent void ratio as that of undisturbed specimen and to preserve the natural water
content of the soil.

15. COMPACTED SPECIMEN
 When compacting disturbed material, it shall be
done employing a mould of circular cross
section. Compacted specimen could also be
prepared at any predetermined water content
and density.
 After the specimen is made, the ends shall be
trimmed perpendicular to the long axis and
faraway from the mould. Representative sample
cuttings shall be obtained or the whole specimen
shall be used for the determination of water
content after the test.

16. THEORY
The load per unit
area at which a
cylindrical specimen
of a cohesive soil fails
fails in compression
is called UCS (qu).
qu = P/A
where P = axial load
at failure
A = Corrected area
= A0/ (1-Ε),
where A0 is the initial
cross-sectional area
of the specimen,
Ε = axial strain =
(Change in length)/
(Original Length)
The undrained shear
strength (Su) of the
soil is equal to one
half of the UCS i.e.
Su = qu / 2.

17. RELEVANCE OF THE EXPERIMENT
 To determine the shear strength of a soil triaxial shear test is
conducted. Also, it’s quick and straightforward to perform.
 The consistency of clay is often determined using the worth
of unconfined compressive strength of soil.
 This should be evaluated as unconfined compression test is
inappropriate for dry sands or crumble clays because the
materials would disintegrate without some land of lateral
confinement.
 Shear strength of a soil the foremost important engineering
property. To settle on the simplest material for the
embankment, one has got to conduct strength tests on the
samples selected.
 If it’s not evaluated then it’ll be needed to conduct the
bearing capacity test within the field which isn’t always
possible.
Sl
No.
Consistency of
Clay
Unconfined Compressive Strength (KN/m2)
1 Very Soft < = 25
2 Soft 25 – 50
3 Medium 50 – 100
4 Stiff 100 – 200
5 Very Stiff 200 – 400
6 Hard > = 400

18. PROCEDURE
 The soil specimen is prepared at the desired water
content and density in the large mould.
 The sampling tube into the large mould is pushed
and the sampling tube which is filled with the soil is
removed.
 The soil sample in the sampling tube is saturated.
 The split mould is lightly coated with a thin layer of
grease.
 The sample is extracted out of the sampling tube
by a suitable method into the split mould, using
the sample extractor and the knife.
 The two ends of the specimen are trimmed off in
the split mould.
 The mould with the specimen is weighed.
 The specimen is removed from the split mould by
splitting the mould into two parts.

19. PROCEDURE
 The length and diameter of the specimen is
measured with Vernier callipers.
 The specimen is placed on the bottom plate of the
compression machine.
 The upper plate is adjusted to make contact with the
specimen.
 The dial gauge and the proving ring gauge is
adjusted to zero.
 The compression load is applied to cause an axial
strain at the rate of ½ to 2% per minute.
 The dial gauge reading is recorded and the proving
ring after every 60 seconds for a strain between 6%
to 12% after every 2 minutes or so beyond 12%.
 The test is continued until failure surfaces have
clearly developed or until an axial strain of 20% is
reached.
 The angle between the failure surface and the
horizontal is measured if possible.

21. OBSERVATION
Elapsed
Time
(minutes)
Compression
Dial reading
Lc=0.01mm
Strain
E=𝛿L/L
(%)
Area (cm2),
Ac= A0/ (1-Ε)
Proving ring dial
reading
1 Div=1Kg
Axial Load(P)
(Kg)
Compressive
Stress(P/Ac)
(Kg/cm²)
0 0 0 11.35 0 0 0
0.5 100 1.32 11.50 1 1 0.09
1.0 200 2.69 11.66 2 2 0.17
1.5 300 3.95 11.82 3 3 0.25
2.0 400 5.26 11.98 5 5 0.42
2.5 500 6.53 12.15 7 7 0.53
3.0 600 7.9 12.32 9 9 0.73
3.5 700 9.21 12.50 11 11 0.83
4.0 800 10.53 12.69 12 12 0.95
4.5 900 11.34 12.97 13 13 1.01
5.0 1000 13.16 13.07 14 14 1.07
5.5 1100 14.47 13.27 14 14 1.06
6.0 1200 15.79 13.43 13 13 0.96

22. Result
 The Unconfined Compressive Strength of Soil is 1.07 Kg/cm².
Graph

23. DISCUSSION
A graph is drawn between compressive stress and strain. The maximum
stress from the curve gives the value of unconfined compressive strength,
qu. If no maximum value of stress is out there, the strain at 20% strain is
taken as unconfined compressive strength. This test provides an immediate
value of the compressive strength of soil in the remoulded condition, it is
carried out within a short time to ensure that no drainage of water is
permitted into or out of the specimen.
In very plastic soils the axial stress does not readily reach a maximum value.

24. REMARKS
 The type of soil in this test depends on the purpose for which it is tested and
may be compacted, remoulded or undisturbed. The specimen has minimum
diameter of 38 mm. Compacted specimen could also be prepared at any
predetermined water content and density.
 Due to lack of stopwatch the readings taken may include some error.
Moreover, the specimen was already prepared so nothing can be said much
about the type of soil specimen.
 Both the ends of the sample are shaped so that it should sit properly on the
bottom plate of loading frame. Rate of loading of the sample should be
constant. Readings should be taken with proper attention so as to have
accurate results. Reading should be taken perpendicularly so as to remove
parallax.
 Unconfined Compressive Strength Test is a special type of Unconsolidated
Undrained (UU) test that is commonly used for clay specimen. It is special in
case of triaxial compression test.

25. REPORT
Unconfined compressive strength (UCS) test was carried out on the
undisturbed soil sample collected from the site in tube sampler. The soil
sample obtained had a diameter of 38 mm and the height of the sample
was trimmed to 76 mm to attain height to diameter ratio of 2 in accordance
with IS 2720 part 10. The value of unconfined compressive strength (q) of the
soil sample was determined in a conventional compression testing
machine at a constant strain rate of 0.6 mm/min in accordance with IS 2720
part 10. The sample was tested upto the breaking/failure load or 20% axial
deformation of the sample, whichever occurred earlier.
UCONFINED COMPRESSION TEST CARRIED OUT AT STATE
INFORMATION COMMISSION (SECTOR-3 PANCHKULA)

26. CALCULATION
Sample Calculation for sample collected from BH-1 (depth 12 m)
 A = initial area of the sample = 11.3 cm²
 Ac= Corrected area of the sample
=A (1-{change in length of specimen during testing/original
length of specimen})
 Original length of specimen 76 mm
 Final length of specimen = 60.8 mm
 Strain in sample at failure = (76-60.8)/76 =20%
Ac=14.1 cm²
Load = 36.1 kg
q=Load/ Ac =2.56 kg/cm²
Undrained Shear strength (Cs) = q /2 = 1.28 kg/cm²

27. THANK YOU