Settlement analysis and environmental assessment of deep mixing binders: A Plaxis 2D study with Volume Averaging Technique
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Wahlgren, Leo
Prahl Blackby, Viktoria
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Constructing road embankments on soft clay is combined with a high risk of excessive
settlements and stability problems. As a ground improvement measure, deep mixing
is often used by injecting cement as columns in the soil to increase the strength and
stiffness. The cement production is a heavy source of green house gas emissions and
implementing cementitious binder substitutes with lower environmental impact is
a vital key for a sustainable construction future. This thesis aimed to investigate
the deep mixing performance on vertical settlements and compare the environmental
impact between SH cement, Multicem and a mixture of 80 % Slag Bremen and
20 % cement.
The vertical settlement assessment was carried out with the finite element software
Plaxis 2D, incorporating Volume Averaging Technique. Volume Averaging Technique
homogenises the material models S-CLAY1S and MNhard in order to capture the
behaviour of enhanced clay, S-CLAY1S for clay and MNhard for mixed columns.
The soil and column data were gathered from both empirical assumptions and a
geotechnical study for an existing road project. A material optimisation process in
terms of volume ratio was performed by investigating the smallest amount of binder
columns necessary to reach the settlement demands for a road embankment. Based
on the volume ratio, each binder’s environmental impact was estimated with a simplified
life cycle assessment.
The results from the optimisation study showed that the binder recipes exhibited a
close range of required volume ratios, despite varying stiffnesses. From the life cycle
assessment estimations, Slag Bremen mixture and Multicem yielded less kg CO2-eq
per meter road section than SH cement, 70 % and 50 % respectively. The most
obvious finding to emerge from this study was that SH cement’s high stiffness did
not compensate for it’s high emissions.
Beskrivning
Ämne/nyckelord
Carbon dioxide equivalents , Volume Averaging Technique , S-CLAY1S , Soft soils , Plaxis 2D , MNhard , Deep mixing , Geotechnics , Life Cycle Assessment , Soft clay