Data and analysis
Student should be able to :
Measure the shearing resistance and shear force parameter ( c&
ϕ ) of cohesive soils which may be undistributed or remolded
The unconfined compressive strength ( ) is the load
per unit area at which the cylindrical specimen of a
cohesive soil falls in compression.
Where P= axial load at failure, A= corrected area
is the initial area of the specimen, =
axial strain = change in length/original length.
The untrained shear strength (s) of the soil is equal to
the one half of the unconfined compressive strength,
Unconfined Compression Testing Machine (Spring Type)
Unconfined Compression Testing Machine (Proving Ring Type)
Load and deformation dial gauge
Sample trimming equipment
1. Excavate a hole in 1 meter depth to get 3 sample of cohesive soil at
suitable site location.
2. Make sure that the samples are in undistributed conditions. Bring the
samples to the laboratory for the further test.
3. Extrude the soil sample from tube sampler. Cut a soil specimen so that
ratio ( L/d ) is approximately between 2 and 2.5.
4. Measure the exact diameter ( d ) ang ( L ) of the specimen. Record to date
5. Weigh the sample and record the mass on data sheet.
6. Calculate the deformation ( ∆L ) corresponding to 15% strain ( ɛ ) .
Strain ( ɛ ) = ∆L / Lo
Where Lo = Original spacimen length ( as measured in step 4 )
7. Carefully place the specimen in the compression device and center it on
the bottom plate. Adjust the device so that the upper plat attached with the
specimen and set the load and deformation dials to zero.
8. Apply the load so that the device produces an axial strain at a rate of
1.0mm per minute, and record the load and deformation dial readings on
the data sheet at starting from 10, 25, 50, 75, 100 devisions on the
9. Keep applying the load until ( 1 ) the load ( load dial ) decreases on the
specimen significantly, ( 2 ) the load holds constant for at least four
deformation dial readings, or ( 3 ) the deformation is segnificantly past
15% strain that was determined in step 6.
10.Draw a sketch to depict the simple failure.
11.Remove the sample from compression device and obtain a sample for
water content determination. Determine the water content.
DATA AND ANALYSIS
1. Convert the dial readings to the appropiate load and length units,
and enter these values on the data sheet in the deformation and
total load columns.
2. Compute the sample cross-sectional area, Ao = π / 4 x (d)2
3. Compute the strain , ɛ = ∆L/Lo
4. Compute the corrected area, A’= Ao /1-ɛ
5. Using A’ , compute the specimen stress , sc = ό = P/A’
6. Compute the water content , w%
7. Plot the stress versus strain on graph paper. Show qu as the peak
stress ( or at 15% strain ) of the test.
8. Draw Mohr’s circle qu step 7 and show the undrained shear
su = c ( or cohesion ) = qu / 2
Clearly more work is needed to quantify the reductionof unconfined
compressive strength in saturatedrocks. From the data collected for
this paper atentative rule of thumb could be proposed for
thepreliminary estimations needed when working withgeomechanics
• well indurated strong rocks:
UCSsat/UCSdry = 0,80-0,90
• cemented medium strength rocks:
UCSsat/UCSdry = 060-0,70
• soft argillaceous rocks:
UCSsat/UCSdry = 0,30
The perimeter purpose of this test is to determine the unconfined
compressive strength which is then used to calculate the
unconsolidated untrained shear strength of the soil under unconfined
conditions. According to the ASTM standard, the unconfined
compressive test strength ( qu) is defined as the compressive stress at
which an unconfined cylindrical specimen of soil will fail in a sample
compression test. The unconfined compressive strength 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.
To determine the unconfined compressive strength which is then used
to calculate the unconsolidated untrained shear strength of the soil
under unconfined conditions.
1. Donald Mcglinchey, Characterisation of bulk solids, 2005, CRC Press DT Afrika.
2. Mazlan Mohammad Abdul Hamid, Standard aggregate sieve analysis TEST, ASTM
International - Standards Worldwide, (July 2008) ASTM C136-06, retrived from
3. Norliza Muhammad, concrete laboratory,(2006). Gradation Test. (2007), Norliza Muhammad,