Field Measurement by Fully Grouted Vibrating Wire Piezometers

Research is being undertaken by Imperial College London to investigate the effects of tunnelling on existing tunnels in London Clay. The research opportunity arose with the Crossrail construction of underground twin-bore railway tunnels through central London where the new tunnels interface with existing networks of London Underground Limited (LUL) tunnels and other utility tunnels. The Crossrail western tunnel section involves construction of twin tunnels using 7.2m diameter earth-pressure-balance tunnel boring machines (TBMs) mostly in London Clay. Comprehensive field monitoring was performed at an instrumented site in Hyde Park to assess the effect of new tunnel construction on both the “greenfield” ground and the ground in the near vicinity of existing segmental cast iron lined tunnels. During the year prior to the passage of TBMs, baseline monitoring work on the installed instruments was carried out. Wan and Standing (2014) describe the instrumentation scheme which includes various types of borehole instruments such as rod extensometers, in-place inclinometers and piezometers.