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The influence of membranes on tests of coarse-grained materials at low cell pressures

The influence of membranes on tests of coarse-grained materials at low cell pressures
The influence of membranes on tests of coarse-grained materials at low cell pressures
In triaxial tests on small specimens of sands/silts and clays, cell pressures are usually greater than 100 kPa and membranes are relatively thin (~0.3 mm). In such tests the influence of the membrane on the stresses on the specimen is small and is usually ignored. Where cell pressures and/or the specimen strength are low the influence of the membrane increases. In such circumstances membrane corrections may be applied assuming right cylinder deformation and thin wall or circular hoop behaviour. However, there are circumstances in which these methods of membrane correction are invalid. For example when the material tested has a large particle size relative to the specimen diameter (e.g. D100 approaches 1/6 of the specimen diameter) membranes behave neither as thin walls nor as circular hoops. Tests on railway ballast fall into this category; the large particles require larger specimens and thicker membranes. The thickness of these membranes is more significant as a proportion of specimen diameter and may have a greater influence on the stresses on the specimen. Furthermore, tests are often carried out at low cell pressures to replicate field conditions where membrane influence is greater. The influence of the membrane in such tests is investigated by means of discrete element method simulations using spherical particles in a face centred cubic packing. The membrane is modelled as an array of points surrounding the specimen and connected elastically. Using a closed form solution for the packing used, the influence of the membrane on initial specimen strength is quantified for differing membrane properties. Furthermore, as a first step to developing a way to correct for membrane influence on large grain sized physical specimens, parameters are identified that correlate to membrane influences.
9781138027077
Le Pen, L.
4a38e256-d113-4bba-b0d4-32d41995928a
Harkness, J.
026f02e8-41d9-403f-83be-0d880058ecf1
Zervos, A.
9e60164e-af2c-4776-af7d-dfc9a454c46e
Powrie, W.
600c3f02-00f8-4486-ae4b-b4fc8ec77c3c
Le Pen, L.
4a38e256-d113-4bba-b0d4-32d41995928a
Harkness, J.
026f02e8-41d9-403f-83be-0d880058ecf1
Zervos, A.
9e60164e-af2c-4776-af7d-dfc9a454c46e
Powrie, W.
600c3f02-00f8-4486-ae4b-b4fc8ec77c3c

Le Pen, L., Harkness, J., Zervos, A. and Powrie, W. (2014) The influence of membranes on tests of coarse-grained materials at low cell pressures. International Symposium on Geomechanics from Micro to Macro, Cambridge, United Kingdom. 31 Aug - 03 Sep 2014. 6 pp .

Record type: Conference or Workshop Item (Paper)

Abstract

In triaxial tests on small specimens of sands/silts and clays, cell pressures are usually greater than 100 kPa and membranes are relatively thin (~0.3 mm). In such tests the influence of the membrane on the stresses on the specimen is small and is usually ignored. Where cell pressures and/or the specimen strength are low the influence of the membrane increases. In such circumstances membrane corrections may be applied assuming right cylinder deformation and thin wall or circular hoop behaviour. However, there are circumstances in which these methods of membrane correction are invalid. For example when the material tested has a large particle size relative to the specimen diameter (e.g. D100 approaches 1/6 of the specimen diameter) membranes behave neither as thin walls nor as circular hoops. Tests on railway ballast fall into this category; the large particles require larger specimens and thicker membranes. The thickness of these membranes is more significant as a proportion of specimen diameter and may have a greater influence on the stresses on the specimen. Furthermore, tests are often carried out at low cell pressures to replicate field conditions where membrane influence is greater. The influence of the membrane in such tests is investigated by means of discrete element method simulations using spherical particles in a face centred cubic packing. The membrane is modelled as an array of points surrounding the specimen and connected elastically. Using a closed form solution for the packing used, the influence of the membrane on initial specimen strength is quantified for differing membrane properties. Furthermore, as a first step to developing a way to correct for membrane influence on large grain sized physical specimens, parameters are identified that correlate to membrane influences.

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More information

Submitted date: 26 August 2014
Published date: September 2014
Venue - Dates: International Symposium on Geomechanics from Micro to Macro, Cambridge, United Kingdom, 2014-08-31 - 2014-09-03
Organisations: Faculty of Engineering and the Environment

Identifiers

Local EPrints ID: 369838
URI: http://eprints.soton.ac.uk/id/eprint/369838
ISBN: 9781138027077
PURE UUID: 7ace26ef-ff16-4601-8489-e6bef726b072
ORCID for L. Le Pen: ORCID iD orcid.org/0000-0002-4362-3895
ORCID for J. Harkness: ORCID iD orcid.org/0000-0001-7598-0080
ORCID for A. Zervos: ORCID iD orcid.org/0000-0002-2662-9320
ORCID for W. Powrie: ORCID iD orcid.org/0000-0002-2271-0826

Catalogue record

Date deposited: 20 Oct 2014 08:11
Last modified: 11 Jul 2020 00:29

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