Unconsolidated Undrained Test

Unconsolidated Undrained Test related to Geo-technical Engineering.

1. Welcome To Our Presentation 1

2. Presentation Topic : unconsolidated undrained Test Group N0: 02 Name & Id: Md. Shahedul Islam Siddikh-14306071 Md. Mozzkkirul Islam-15106029 Saiful Islam Bappy - 15106140 Mst . Mousumy Akter - 15106144 Saiful Islam Sajjad-15106156 S.M. Ferose Iqbal - 15206005 2

3. Types of Triaxial Tests Is the drainage valve open? yes no C onsolidated sample U nconsolidated sample Under all-around cell pressure  c Step 1 Is the drainage valve open? yes no D rained loading U ndrained loading Shearing (loading) Step 2 CD test CU test UU test

4. What is UU test?? UU (unconsolidated undrained ) test is type of triaxial test. In this test: The confining pressure is not zero. We need to test at least three samples at different confining pressure to obtain the Mohr- Coulobm failure circles. This is also a quick test, as it is undrained . The test can be performed in any type of soil.

5. Definitions, Objectives and Applications Objective To determine the shear strength of the soil by Unconsolidated Undrained test. Equipment • Triaxial Machine • Specimen preparation equipment • Sample extruder • Balance oven Right-circular cylindrical specimen of cohesive soil;

6. Equipment set up

7. Significance and Applications • A quick test to obtain the shear strength parameters of both fine and coarse grained soils. • The test is not applicable when the rate of construction is slow allowing consolidation of soil. • Hence the test is representative of soils in construction sites where the rate of construction is very fast and the pore waters do not have enough time to dissipate. • Total stress parameters are obtained as portion of load applied is also received by the water. • Quick results. Economical testing. The designs using UU parameters are mostly conservative.

8. Test Procedure Remolded specimens are prepared in the laboratory If testing undisturbed specimens retrieved from the ground by various sampling techniques, trim the samples into regular triaxial specimen dimensions (2.8” x 5.6”) There will be a significant variation in strength of undisturbed and remolded samples Measure the diameter and length of the specimen to be tested If curing the sample (treated soils), wrap the samples in a geotextile and then a zip bag. Place the sample in a humidity room maintained at a relative humidity of 90%.

9. Test Procedure 6. Prior to testing, avoid any moisture loss in the sample, place on a triaxial base (acrylic). The ends of the sample are assumed to be frictionless . 7. The triaxial cell is placed above the sample and required confinement is applied simulating the effect of surrounding soil at that depth 8.The rate of strain is maintained at 1.2700 mm/min as per ASTM specifications. 9.The data acquisition system collects real time data and the test is stopped when there is a drop observed in the strain versus load plot.

10. Equation of Ā Skempton’s pore water pressure parameter Ā was defined in Eq : Ā = Δud / Δσd at failure, the parameter Ā can be written as Ā = Āf = ( Δ ud )f / ( Δσ d)f The general range of Āf values in most clay soils is as follows:  Normally consolidated clays: 0.5 to 1  Overconsolidated clays: -0.5 to 0 Major principal stress at failure (total): σ 3 + ( Δσ d ) f = σ 1  Major principal stress at failure (effective) : σ 1 - ( Δσ u ) f = σ' 1  Minor principal stress at failure (total): σ 3  Minor principal stress at failure (effective): σ 3 - ( Δσ u ) f = σ' 3 In these equations, ( Δσ u ) f = pore water pressure at failure. The preceding derivations show that σ 1 - σ 3 = σ' 1 - σ' 3

11. Mohr’s circles

12. Test-1

13. Test-2

14. Test-3

15. Conclusion: The tests were completed on progressively denser soil samples . The undrained shear strength for a dry compacted soil specimen may range to over 50 psi. The first two tests had values of 45.9 psi ad 42.35psi. While the third value is 55.39 psi, due partial saturation of the sample, the results may not be valid.

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