Alternative Methods for Quick-Clay Mapping

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Examensarbete för masterexamen
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2022
Författare
Sundström, Lisa
Waerme, Alexander
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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.
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Undrained shear strength, PCA, Cyclic T-bar penetration test, TPT, CPT, quick clay
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