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LABORATORY TESTING RELATED TO UNLOADING MODULUS OF SOFT CLAY

Hasselberg, Sofia LU (2018) In TVGT-5000 VGTM01 20181
Geotechnical Engineering
Department of Construction Sciences
Abstract
The unloading modulus, together with the permeability, are responsible for the swelling process of a soil that is subjected to unloading. Studies to examine the unloading modulus of clay has previously been performed and several relationships describing this parameter has hence been developed. The methods to study the unloading modulus has previously been both laboratory studies and field measurements. The laboratory studies has generally focused on using incremental loading (IL) oedometer tests.
This master thesis has three aims:
• Examine if the storage time of the samples will affect the obtained unloading modulus for soft clay.
• To investigate if modified CRS-tests can be used in order to determine the unloading modulus of soft... (More)
The unloading modulus, together with the permeability, are responsible for the swelling process of a soil that is subjected to unloading. Studies to examine the unloading modulus of clay has previously been performed and several relationships describing this parameter has hence been developed. The methods to study the unloading modulus has previously been both laboratory studies and field measurements. The laboratory studies has generally focused on using incremental loading (IL) oedometer tests.
This master thesis has three aims:
• Examine if the storage time of the samples will affect the obtained unloading modulus for soft clay.
• To investigate if modified CRS-tests can be used in order to determine the unloading modulus of soft clay in the same extent as IL-tests.
• Investigate if one set of model parameters, obtained from PLAXIS 2D and restricted to the Soft soil creep model, can describe the behaviour of the soil when exposed to both compression and unloading.
Piston sampler of the type STI was used in order to retrieve undisturbed samples of clay to performed laboratory tests on. Samples from 3 levels; 17 m, 20 m, and 25 m were obtained from one location in central Gothenburg, Sweden. Standard CRS-tests were initially perform in order to develop an understanding of the stress history of the clay and serve as the basis for determining the unloading sequences of the samples from the borehole. Two rounds of unloading tests, using modified CRS-tests, were performed on samples with 8 weeks of storage time in between.
There could not be found any tendency that suggested that the unloading modulus of soft clay is affected by storage time. The clay in these specific sample tubes however had a tendency to swell extensively which might have affected the initial tests. The result from the performed tests showed that modified CRS-test appears to work satisfactory in order to capture the unloading behaviour of soft clay in the same extent as IL-tests. The data showed that the unloading modulus, obtained with modified CRS-test, was larger for unloading sequences above the in-situ pre-consolidation pressure than below.
If the set of parameters, that was obtained for compression of the clay in the software PLAXIS 2D and the material model Soft soil creep, was used to also describe the behaviour of the soil during unloading, the magnitude of the expansion of the soil was underestimated. (Less)
Popular Abstract (Swedish)
När jord avlastas kan denna svälla, något som kan ge tryck och således skador på konstruktionsdelar som har kontakt med den svällande jorden. Det är därför av stor vikt att ha kunskap om hur jorden beter sig vid avlastning och detta undersöks vanligtvis i geotekniska laboratorier. I detta examensarbete studerades svällningen av lera, erhållen från Göteborgområdet, som avlastas med hjälp av en modifierad variant av en ofta använd laboratoriemetod. Det undersöktes även vilken effekt som en lagringstid för proverna på 8 veckor hade på resultatet.
Please use this url to cite or link to this publication:
author
Hasselberg, Sofia LU
supervisor
organization
course
VGTM01 20181
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
CRS, unloading modulus, storage time, clay
publication/series
TVGT-5000
report number
TVGT-5062
ISSN
0349-4977
language
English
id
8958945
alternative location
http://www.geoteknik.lth.se/english/publications/tvgt-5000/
date added to LUP
2018-09-27 13:43:41
date last changed
2018-10-19 15:58:53
@misc{8958945,
  abstract     = {{The unloading modulus, together with the permeability, are responsible for the swelling process of a soil that is subjected to unloading. Studies to examine the unloading modulus of clay has previously been performed and several relationships describing this parameter has hence been developed. The methods to study the unloading modulus has previously been both laboratory studies and field measurements. The laboratory studies has generally focused on using incremental loading (IL) oedometer tests. 
This master thesis has three aims:
•	Examine if the storage time of the samples will affect the obtained unloading modulus for soft clay.
•	To investigate if modified CRS-tests can be used in order to determine the unloading modulus of soft clay in the same extent as IL-tests.
•	Investigate if one set of model parameters, obtained from PLAXIS 2D and restricted to the Soft soil creep model, can describe the behaviour of the soil when exposed to both compression and unloading. 
Piston sampler of the type STI was used in order to retrieve undisturbed samples of clay to performed laboratory tests on. Samples from 3 levels; 17 m, 20 m, and 25 m were obtained from one location in central Gothenburg, Sweden. Standard CRS-tests were initially perform in order to develop an understanding of the stress history of the clay and serve as the basis for determining the unloading sequences of the samples from the borehole. Two rounds of unloading tests, using modified CRS-tests, were performed on samples with 8 weeks of storage time in between. 
There could not be found any tendency that suggested that the unloading modulus of soft clay is affected by storage time. The clay in these specific sample tubes however had a tendency to swell extensively which might have affected the initial tests. The result from the performed tests showed that modified CRS-test appears to work satisfactory in order to capture the unloading behaviour of soft clay in the same extent as IL-tests. The data showed that the unloading modulus, obtained with modified CRS-test, was larger for unloading sequences above the in-situ pre-consolidation pressure than below.
If the set of parameters, that was obtained for compression of the clay in the software PLAXIS 2D and the material model Soft soil creep, was used to also describe the behaviour of the soil during unloading, the magnitude of the expansion of the soil was underestimated.}},
  author       = {{Hasselberg, Sofia}},
  issn         = {{0349-4977}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{TVGT-5000}},
  title        = {{LABORATORY TESTING RELATED TO UNLOADING MODULUS OF SOFT CLAY}},
  year         = {{2018}},
}