Unconfined Compression Test 1r1934

MOHAMMAD YUNUS SALEHI I11007770 EXPERIMENT 4: UNCONFINED COMPRESSION TEST

Theory: Purpose: The primary purpose of this test is to determine the unconfined compressive strength, which is then used to calculate the unconsolidated undrained shear strength of the clay under unconfined conditions. According to the ASTM standard, the unconfined compressive strength (qu) is defined as the compressive stress at which an unconfined cylindrical specimen of soil will fail in a simple compression test. In addition, in this test method, 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. Significance: For soils, the undrained shear strength (σu) is necessary for the determination of the bearing capacity of foundations, dams, etc. The undrained shear strength (σu) of clays is commonly determined from an unconfined compression test. The undrained shear strength (σu) of a cohesive soil is equal to one-half the unconfined compressive strength (qu) when the soil is under the ɸ = 0 condition (ɸ= the angle of internal friction). The most critical condition for the soil usually occurs immediately after construction, which represents undrained conditions, when the undrained shear strength is basically equal to the cohesion (c).This is expressed as:

σu = c = qu/2 strength ( s), is given by s = c + σ tan ɸ

Calculation: Proving ring calibration = 0.944 (kn/div) Ao = Initial height of the specimen Ho = Initial height of the specimen Undisturbed: Ao = (3.14/4) x 37² = 1074.665 mm² Ho = 77 mm, D = 37 mm, Weight = 0.1775 Disturbed: Ho = 77 mm, D = 37 mm, Weight = 0.1725

Deformation dial , ∆H(mm) (1)

Undisturbed 0 0.78 1.56 2.32 3.1 3.85 Disturbed 1 1.91 2.84 3.75 4.68 5.6

Unit strain, Ɛ(mm/mm) (2)= ∆H/Ho

Cross sectional area , A(mm²) (3)=Ao/(1- Ɛ)

Proving ring dial(mm) (4)

Applied axial load ,P(kn) (5)=(4 ) X proving ring calibration

Load per unit area (kn/mm²) (6)=(5)/(3)

0 0.01 0.02 0.03 0.04 0.05

1074.665 1085.52 1096.597 1107.902 1119.443 1131.226

0 25 49 75 97 115

0 23.6 46.256 70.8 91.568 108.56

0 0.022 0.042 0.064 0.082 0.096

0.013 0.025 0.037 0.049 0.061 0.073

1088.82 1102.221 1115.955 1130.037 1144.478 1159.293

20 38 58 80 97 105

18.88 35.872 54.752 75.52 91.568 99.12

0.017 0.033 0.049 0.067 0.08 0.086

Undisturbed:

Load per Unit Area vs. Unit Strain 100 90 Load (kn/mm²) x 10ˉ²

80 70 60 50 load

40 30 20 10 0 0.01

0.02

0.03 Strain (mm/mm)

qu = 0.096 kN/mm² C = qu /2 = 0.096/2 = 0.048

0.04

0.05

Disturbed:

Load per Unit Area vs. Unit Strain 100 90 Load (kn/mm²) x 10ˉ²

80 70 60 50 load

40 30 20 10 0 0.013

0.025

0.037

0.049

Strain (mm/mm)

qu = 0.086 kN/mm² C = qu /2 = 0.086/2 = 0.043

0.061

0.073

Discussion:

Conclusion: