On the Northern section of the Dublin Port Tunnel project the main contractor (NMI Consortium) constructed a 60m diameter x 25m deep shaft as a launch chamber for the Tunnel Boring Machines and muck-away from the tunnelling operation.
The shaft was constructed using diaphragm wall techniques. ITM installed instrumentation to monitor the shaft during the construction (excavation) period and also in the long term.
ITM engineers fixed Inclinometer Casings and Embedment Strain Gauges to the diaphragm wall cages prior to installation, then supervised the installation of the cages and concreting operation.
On completion of the installation, base readings and spiral surveys of the Inclinometer Casings were carried out before handing over to the main contractor for monitoring.
Due to a gantry being installed over two of the Inclinometer locations, strings of IPI (In-place Inclinometers) sensors were installed and cabled back to a data logger to enable remote monitoring to be carried out. I-Site software was installed for the processing and presentation of this data.
To monitor the water pressure behind and below the shaft, Vibrating Wire Piezometers were installed. These were cabled back to a data logger at the top of the shaft, which was equipped with a modem and programmed to send text messages to site engineers mobile phones, should the water pressure reach a pre-agreed target level, thus enabling the engineers to control the de-watering operation.
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