Freezing has finished!

6 May 2001 17:23 - BAM International bv

Interbeton has finally shut down the ground freezing equipment in Boston now that a 116 metre long tunnel has been pushed into position.

'Since the trains have to keep rolling overhead, we froze the soil to stabilise it at three points beneath the tracks. Excavators have been working 24 hours a day, six days a week, to remove the frozen soil, advancing 90 centimetres at a time. Huge jacks then pushed the tunnel boxes into the excavated space. Either two or three boxes form the tunnels. This method of tunnelling is known as box jacking', explains project engineer Pieter van Dijk. The combined ground freezing and jacking concept was developed with the help of Doug Allenby of Nuttall and John Ropkins of John Ropkins Ltd. They were both actively involved in the detailed development of the system in Boston. Nuttall and Ropkins have extensive experience of using the method in the United Kingdom. The project is part of the largest infrastructure project in the United States, known as the Big Dig.