Branston, Michael William (2003) The application of time-lapse microgravity to investigate and monitor subsidence related to salt dissolution. Doctoral thesis, Keele University.

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Subsidence of the ground surface due to the removal of support either through man’s mining activity or natural dissolution of rock occurs throughout the world. In Cheshire, subsidence related to salt extraction has occurred in various forms for centuries, the most frequent and devastating occurring in the 18th and 19th centuries. Subsidence in Cheshire has restricted the industrial development of areas with a history of salt extraction and jeopardised the stability of urban areas.
It is important for the remediation of such sites, that the cause of subsidence and it’s state of development is established. Increasingly, practitioners are looking toward cost effective, non-invasive techniques to rapidly assess subsidence afflicted areas.
This thesis investigates the potential of one such technique, time-lapse microgravity. Microgravity has become established as a tool for use during site investigations where the characterisation of sub-surface density contrasts is required. The objective of this thesis is to develop this technique into a tool for the characterisation and monitoring of areas experiencing surface subsidence.
Preliminary trials were conducted at Preesall Brine field (Lancashire) and Keele University (Staffordshire) to verify that time-lapse microgravity was an accurate and viable technique. A case investigation was conducted at an urban site in Northwich, Cheshire known to be experiencing subsidence related structural problems. Gravity modelling and inversion techniques were employed to identify the causative body’s dimensions and monitor its development over a four-year period.
Further filed trials were carried out at Marston, Cheshire. A major mass deficiency was identified as cause of the subsidence in the area using gravity modelling techniques but sub-surface mass movement was not identified during the monitoring period.
Interpretation of passive microseismic data, acquired alongside the time-lapse microgravity surveys, has provided information on the mechanism of failure responsible for the subsidence recorded at the test sites.
This work has shown that time-lapse microgravity is a viable, cost effective, non- invasive monitoring technique that is beneficial in the assessment and characterisation of subsidence affected areas as well as providing information valuable to the assessment of the remediation of such areas.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QE Geology
Divisions: Faculty of Natural Sciences > School of Geography, Geology and the Environment
Contributors: Styles, P (Thesis advisor)
Depositing User: Lisa Bailey
Date Deposited: 13 Sep 2019 11:45
Last Modified: 13 Sep 2019 11:45

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