1. Unconfined Compression Test ASTM D-2166 /02
Experiment No. 8
Unconfined Compression Test
ASTM D-2166 /02
Soil Mechanics Lab CE 350
Unconfined Compression

2. Unconfined Compression
Soil Mechanics Lab CE 350
Unconfined Compression

3. Unconfined Compression
Content
Objective
Definitions
Required Apparatus
Data and calculations
Determination of Shear Strength Parameters
Applications
Soil Mechanics Lab CE 350
Unconfined Compression

4. Unconfined Compression
Objective
Determine the shear strength of cohesive soil.
Soil Mechanics Lab CE 350
Unconfined Compression

5. Unconfined Compression
Definitions
the unconfined compression test is considered a form of triaxial test in which the major principal stress is equal to the applied axial stress and the minor principal stress is equal to zero.
The unconfined compressive strength, qu, is defined as the maximum compressive stress at failure
Soil Mechanics Lab CE 350
Unconfined Compression

6. Unconfined Compression
REQUIRED APPARATUS
Unconfined compression device (electrically driven strain-controlled device is recommended). Specimen trimmer (if undisturbed sample is tested).
Remolding device (if remolded sample is tested).
Dial gage for measuring
axial deformation.
Caliper for measuring
specimen dimensions.
Timer.
Balance, sensitive to 0.01 g.
Soil Mechanics Lab CE 350
Unconfined Compression

7. REQUIRED MEASUREMENTS
Diameter specimen, D0
Length of specimen, L
Initial moisture content, wi
Final moisture content, wf
Total specimen weight before testing, Wi
Total specimen weight after test, Wf
Vertical deformation gage reading at time, ti
Proving ring reading at time, ti
Soil Mechanics Lab CE 350
Unconfined Compression

8. Unconfined Compression
SAMPLE PREPARATION
Undisturbed Sample
Remolded Sample
Soil Mechanics Lab CE 350
Unconfined Compression

9. Unconfined Compression
Aspect Ratio
2 < H/D < 3
H/D < 3 To prevent buckling action
H/D > 2 To prevent fraction between load plate and surface of specimen
Soil Mechanics Lab CE 350
Unconfined Compression

10. DATA AND CALCULATIONS Ac = Ao/(1-Δh/Lo) qu = P/Ac
Deformation. dial reading
(div.)
Deformation dh (mm)
Load ring reading
Strain
(dh/h)
Corrected area
Axial force (P)
(N)
Axial stress qu (N/cm2) R1
R1*C1 R2
dh/h
R2*C2
Ac = Ao/(1-Δh/Lo)
qu = P/Ac
Soil Mechanics Lab CE 350
Unconfined Compression

11. PRESENTATION OF RESULTSqu
Peak
Constant
Soil Mechanics Lab CE 350
Unconfined Compression

12. Unconfined Compression
Mohr’s Circle qu qu qu
Soil Mechanics Lab CE 350
Unconfined Compression

13. Unconfined Compression
Mode Of Failure
Shapes of Specimens at Failure
Brittle Failure
Semi Plastic
Plastic
Soil Mechanics Lab CE 350
Unconfined Compression

14. Unconfined Compression
Applications
Prediction of soil behavior
Estimation of bearing capacity
Estimation of bearing capacity of pils
Estimation of lateral earth pressure
Soil Mechanics Lab CE 350
Unconfined Compression