Category: Soil Mechanics

Why φu ≠ 0 in Unconsolidated-Undrained Triaxial Testing

For partly saturated soils, the Mohr failure envelope is curved at low confining pressures.

The curved part is due to presence of undissolved air voids, which is compressible.

As the air voids compress with increasing confinement, the envelope continues to become flatter.

When all air is dissolved in the pore water, the specimen is completely saturated, and the envelope becomes horizontal.

The undrained shear strength obtained at full saturation depends on the initial degree of saturation.

References:

P.V.Lade (2016). Triaxial Testing of Soils: John Wiley & Sons.

Sedimentation of silt & clay particles

Classification of fine soil is basically depends on sedimentation process of silt and clay, which consists of different particle size. Silt is bigger compared to clay, so it will settle faster than clay. Head (2006) provides approximation on terminal velocity for each particle size, based on the so called Stokes’ Law.

Particle Terminal velocity [mm/s] Approximate diameter [µm]
Coarse silt 1 35
Medium silt 0.1 12
Fine silt 0.01 3.5
Clay 0.001 1.2

From the provided value, the time required for the particles to settle for certain depth can be estimated using usual relationship between velocity and depth.

References:

K.H.Head (2006). Manual of Soil Laboratory Testing, Volume 1 Soil Classification and Compaction Tests, 3rd Edition: CRC Press

Malaysian Standard for Geotechnical Engineering

Mostly, when it is necessary to refer for standards for conducting laboratory works, field works or design, Malaysian civil engineer will refer British Standard.

However, two important by-laws that are related to civil engineering work, clearly stated that Malaysian Standard should be referred, instead of British Standard.

1.Uniform Building By-Laws (UBBL) (1984)

257. In these By-laws where there is any reference to the British Standard Specifications or British Code of Practice and there is, whether on the date of the coming into operation of these By-laws or subsequently, a corresponding Malaysian Standard Specification or Malaysian Code of Practice in respect of that subject, the Malaysian Standard Specification or Malaysian Code of Practice shall be deemed to have superseded the British Standard Specification or British Code of Practice respectively and shall be deemed to apply.

2.Earthworks By-Laws (EBBL)

Unlike UBBL, EBBL is not uniform, as any local authority can make their own EBBL. In case for State of Kedah, they have decide to have uniform law for the whole state in Undang-Undang Kecil Kerja Tanah (Pihak Berkuasa Tempatan Negeri Kedah) 2016.

” Jika ada dikeluarkan suatu Tataamalan Piawaian Malaysia yang bersamaan selepas mula berkuatkuasanya Undang-Undang Kecil ini, maka ia hendaklah menggantikan British Standards Code of Practice mengenai hal perkara yang sama dan hendaklah dipatuhi: Dengan syarat bahawa ia tidak menyentuh pelan dan spesifikasi yang telah diluluskan di bawah British Standards Code of Practice atau kerja tanah yang dijalankan di bawahnya. “

Table below shows equivalence between British Standard/Eurocode and Malaysian Standard:

No. British Standard / Eurocode Malaysian Standard Remarks
1 BS 1377-1:2016 Methods of test for soils for civil engineering purposes. General requirements and sample preparation MS 1056-1:2005 (Confirmed:2013) Soils For Civil Engineering Purposes – Test Method – Part 1: General Requirements And Sample Preparation (First Revision) Soil Laboratory
2 BS 1377-2:1990. Methods of test for soils for civil engineering purposes. Classification tests MS 1056-2:2005 (Confirmed:2013)  Soils For Civil Engineering Purposes – Test Method – Part 2: Classification Tests Soil Laboratory
3 BS 1377-3:2018. Methods of test for soils for civil engineering purposes. Chemical and electro-chemical testing MS 1056-3:2005 (Confirmed:2013)  Soils For Civil Engineering Purposes – Test Method – Part 3: Chemical And Electro – Chemical Tests Soil Laboratory
4 BS 1377-4:1990. Methods of test for soils for civil engineering purposes. Compaction-related tests MS 1056-4:2005 (Confirmed:2013) Soils For Civil Engineering Purposes – Test Method – Part 4: Compaction-Related Tests Soil Laboratory
5 BS 1377-5:1990. Methods of test for soils for civil engineering purposes. Compressibility, permeability and durability tests MS 1056-5:2005 (Confirmed:2013) Soils For Civil Engineering Purposes – Test Method – Part 5: Compressibility, Permeability And Durability Tests Soil Laboratory
6 BS 1377-6:1990. Methods of test for soils for civil engineering purposes. Consolidation and permeability tests in hydraulic cells and with pore pressure measurement MS 1056-6:2005 (Confirmed:2013) Soils For Civil Engineering Purposes – Test Method – Part 6: Consolidation And Permeability Tests In Hydraulic Cells And With Pore Pressure Measurement Soil Laboratory
7 BS 1377-7:1990. Methods of test for soils for civil engineering purposes. Shear strength tests (total stress) MS 1056-7:2005 (Confirmed:2013) Soils For Civil Engineering Purposes – Test Method – Part 7: Shear Strength Tests (Total Stress) Soil Laboratory
8 BS 1377-8:1990. Methods of test for soils for civil engineering purposes. Shear strength tests (effective stress) MS 1056-8:2005 (Confirmed:2013) Soils For Civil Engineering Purposes – Test Method – Part 8: Shear Strength Tests (Effective Stress) Soil Laboratory
9 BS 1377-9:1990. Methods for test for soils for civil engineering purposes. In-situ tests MS 1056: Part 9:2005 Soils For Civil Engineering Purposes – Test Method – Part 9: In-Situ Tests Soil Laboratory
10 BS 5930:2015. Code of practice for ground investigations MS 2038:2006   Site Investigations – Code Of Practice Geotechnics –Site Investigations
11 BS 6031:2009. Code of practice for earthworks. MS 1754:2004 (Confirmed:2015) Earthworks – Code Of Practice Geotechnics – Slope stability
12 BS 8004:2015. Code of practice for foundations. MS 1756:2004 (Confirmed:2015) Foundations – Code Of Practice Geotechnics – Shallow and deep foundations
13 BS 8002:2015. Code of practice for earth retaining structures. Not Available Geotechnics – Earth Retaining Structures
14 MS EN 1990:2010 (National Annex) Malaysia National Annex To Eurocode – Basis Of Structural Design
15 BS EN 1990:2002+A1:2005. Eurocode. Basis of structural design. MS EN 1990:2010 Eurocode – Basis Of Structural Design Geotechnics – Slope stability, Shallow and deep foundations, Earth Retaining Structures
16 MS EN 1997-1:2012 (National Annex) Malaysia National Annex To Eurocode 7: Geotechnical Designs – Part 1: General Rules
17 BS EN 1997-1:2004+A1:2013. Eurocode 7. Geotechnical design. General rules MS EN 1997-1:2012 Eurocode 7: Geotechnical Design – Part 1: General Rules Geotechnics – Slope stability, Shallow and deep foundations, Earth Retaining Structures
18 MS EN 1997-2:2016 (National Annex) Malaysia National Annex To Eurocode 7: Geotechnical Design – Part 2: Ground Investigation And Testing
19 BS EN 1997-2:2007. Eurocode 7. Geotechnical design. Ground investigation and testing MS EN 1997-2:2015 Eurocode 7: Geotechnical Design – Part 2: Ground Investigation And Testing Soil Laboratory   Geotechnics –Site Investigations

References:

  1. Uniform Building By-Laws (UBBL) (1984)
  2. Undang-Undang Kecil Kerja Tanah (Pihak Berkuasa Tempatan Negeri Kedah) 2016

Easier method for determining Plastic Limit

Easier method for determining Plastic Limit had been introduced by Feng (2000). By utilizing this method, there is no necessity to conduct rolling test, as for this test, the result might be dependent on the operator.

This new method can be simplified as follows:

  • Plot results from fall cone method in log scale for both x- and y-axes. X-axis represents penetration (mm) and y-axis represents water content (%).
  • Construct the best straight line from the points.
  • Extend the straight line to y-axis. The point where the line cross y-axis (when penetration = 1mm) is known as C.
  • Measure the slope of the line, m.
  • Plastic Limit, PL = C(2)^m.

Example are as shown in figure below (Budhu, 2010):

References:

  1. Budhu, M. (2010). Soil Mechanics and Foundations: John Wiley and Sons.
  2. Feng, T. W. (2000). Fall-cone penetration and water content relationship of clays. Geotechnique, 50(2), 181–187.