Exploratory Data Analysis of the Large Scale Gas Injection Test (Lasgit)

Bennett, Daniel 2014. Exploratory Data Analysis of the Large Scale Gas Injection Test (Lasgit). PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis presents an Exploratory Data Analysis (EDA) performed on the dataset arising from the operation of the Large Scale Gas Injection Test (Lasgit). Lasgit is a field scale experiment located approximately 420m underground at the Äspö Hard Rock Laboratory (HRL) in Sweden. The experiment is designed to study the impact of gas build-up and subsequent migration through the Engineered Barrier System (EBS) of a KBS-3 concept radioactive waste repository. Investigation of the smaller scale, or ‘second order’ features of the dataset are the focus of the EDA, with the study of such features intended to contribute to the understanding of the experiment. In order to investigate Lasgit’s substantial (26 million datum point) dataset, a bespoke computational toolkit, the Non-Uniform Data Analysis Toolkit (NUDAT), designed to expose and quantify difficult to observe phenomena in large, non-uniform datasets has been developed. NUDAT has been designed with capabilities including non-parametric trend detection, frequency domain analysis, and second order event candidate detection. The various analytical modules developed and presented in this thesis were verified against simulated data that possessed prescribed and quantified phenomena, before application to Lasgit’s dataset. The Exploratory Data Analysis of Lasgit’s dataset presented in this thesis reveals and quantifies a number of phenomena, for example: the tendency for spiking to occur within groups of sensor records; estimates for the long term trends; the temperature profile of the experiment with depth and time along with the approximate seasonal variation in stress/pore-water pressure; and, in particular, the identification of second order event candidates as small as 0.1% of the macro-scale behaviours in which they reside. A selection of the second order event candidates have been aggregated together into second order events using the event candidates’ mutual synchronicities. Interpretation of these events suggests the possibility of small scale discrete gas flow pathways forming, possibly via a dilatant flow mechanism. The interpreted events typical behaviours, in addition to the observed spiking tendency, also support the grouping of sensors by sensor type. The developed toolkit, NUDAT, and its subsequent application to Lasgit’s dataset have enabled an investigation into the small scale, or ‘second order’ features of the experiment’s results. The analysis presented in this thesis provides insight into Lasgit’s experimental behaviour, and as such, contributes to the understanding of the experiment.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Engineering
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Uncontrolled Keywords:	Radioactive Waste; Forge; Lasgit; Gas Migration; Bentonite; Non-Uniform Data Analysis.
Funders:	European Atomic Energy Community’s Seventh Framework Programme
Date of First Compliant Deposit:	30 March 2016
Last Modified:	24 Jun 2017 10:49
URI:	https://orca.cardiff.ac.uk/id/eprint/66203

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