Page 18 - Grp3-Soil magazine (Final-Vid ver)

I
F
N
D
E
N
U

)
O
C
N
S
S
E
N
O
I
O
C

R
P
M
B
(
(B) UNCONFINED COMPRESSION
(B) UNCONFINED COMPRESSION
H
C

G
S
T
T

(
U
E
S
T
E
R
T
S
N
STRENGTH TEST (UCS)
)
STRENGTH TEST (UCS)
The setup is like triaxial system (refer to
figure 4), this shears a specimen under
axial load with no confining pressure,
σ3=0. Hence, failure envelope is
horizontal. However, this test limited to
cohesive soil only.
Formulas:
Initial area of sample, Ao=(π x d2)/4
Cross-section of sample at failure,
Ac=Ao/(1-ε) Figure 3(a): Graph of Shear Stress vs Normal Stress with
Normal stress, σ=F/A no confining pressure, σ3=0
Strain, ε=∆L/L
Major principal stress, σ1=σf
Stress at failure, σf =P/Ac
Cohesion, cu=qu/2
The unconfined compressive strength (qu)
is taken as the maximum load attained
per
unit area, or the load per unit area at 15%
axial strain, whichever occurs
first during the performance of a test.
UCS Test Procedure

Figure 3(a) & (b): Mohr-Coulomb Plot of UCS Test

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