CUED Publications database

Fibre optic monitoring of a deep circular excavation

Schwamb, T and Soga, K and Mair, RJ and Elshafie, MZEB and Sutherden, R and Boquet, C and Greenwood, J (2014) Fibre optic monitoring of a deep circular excavation. Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, 167. pp. 144-154. ISSN 1353-2618

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This paper describes part of the monitoring undertaken at Abbey Mills shaft F, one of the main shafts of Thames Water's Lee tunnel project in London, UK. This shaft, with an external diameter of 30 m and 73 m deep, is one of the largest ever constructed in the UK and consequently penetrates layered and challenging ground conditions (Terrace Gravel, London Clay, Lambeth Group, Thanet Sand Formation, Chalk Formation). Three out of the twenty 1-2 m thick and 84 m deep diaphragm wall panels were equipped with fibre optic instrumentation. Bending and circumferential hoop strains were measured using Brillouin optical time-domain reflectometry and analysis technologies. These measurements showed that the overall radial movement of the wall was very small. Prior to excavation during a dewatering trial, the shaft may have experienced three-dimensional deformation due to differential water pressures. During excavation, the measured hoop and bending strains of the wall in the chalk exceeded the predictions. This appears to be related to the verticality tolerances of the diaphragm wall and lower circumferential hoop stiffness of the diaphragm walls at deep depths. The findings from this case study provide valuable information for future deep shafts in London. © ICE Publishing: All rights reserved.

Item Type: Article
Divisions: Div D > Construction Engineering
Div D > Geotechnical and Environmental
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:16
Last Modified: 22 Oct 2020 05:11
DOI: 10.1680/geng.13.00036