Alternative Methods for Quick-Clay Mapping
Typ
Examensarbete för masterexamen
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2022
Författare
Sundström, Lisa
Waerme, Alexander
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Construction and development in quick-clay areas is often associated with great
challenges. The conventional method for confirming quick-clay deposits in Sweden is
undisturbed soil sampling and subsequent laboratory testing. Reliable geotechnical
field investigation methods that could reduce the need for time consuming and costly
undisturbed soil sampling with following laboratory work has for a long time been
desired in the geotechnical industry. The overall objective of this thesis has been to test
three methods that potentially could be used to simplify the process of quick-clay
mapping. Two of the methods focused on refining existing geotechnical field
investigation methods. First, multiple cone penetration tests (CPT) were performed in
the exact same location. Second, a cyclic T-bar penetration test (TPTc) was performed
by letting the T-bar penetrometer circulate between two predefined depths before being
penetrated down to another cyclic level. Both methods were executed to obtain data
that was then used to evaluate the undisturbed and remoulded undrained shear strengths.
The main finding when performing three consecutive CPT soundings were that it could
not be seen as a reliable method for evaluation of the remoulded undrained shear
strength. A decrease in penetration resistance was however noted, which is implying
that the clay gets disturbed. Uncertainties related to difficulties with performing all
soundings following the same path and uncertainties regarding if the consecutive
soundings are remoulding the clay enough, where the main difficulties found. The
evaluated undrained shear strength from the TPTc proved to give reasonable results for
the undisturbed undrained shear strength. For the remoulded conditions the results
showed that at depth where sufficiently many cycles were made, the remoulded
undrained shear strength corresponded well with the laboratory results. There are
uncertainties regarding the correction factor for evaluation of the undrained shear
strength since there is yet no empirical relation for what correction factor to use. The
third and last method was focusing on developing statistical tools to potentially find
relations between results from field- and laboratory investigations. One method that
was tested were to perform a statistical analysis using principal component analysis
(PCA). The results of that analysis showed no clear relations between the parameters
collected from laboratory results and parameters collected from field results, at least
not on a regional scale. Another method was to evaluate the impact of draining soil
layers on the formation of quick clay. The distance to a draining layer was compared to
the corresponding remoulded undrained shear strength evaluated with fall cone test.
The comparison did however not show any strong general correlations.
Beskrivning
Ämne/nyckelord
Undrained shear strength , PCA , Cyclic T-bar penetration test , TPT , CPT , quick clay