European practice in geotechnical instrumentation for tunnelconstruction control - Part 2

In continental Europe, the following trends can be identified in the use of geotechnical instrumentation in the control of tunnel construction procedures: &bull Generally, the geotechnical instrumentation market sector applied in the control of construction procedures is significantly more dynamic than the traditional sector of performance monitoring for design purposes; &bull DIBIT, a new tunnel scanner based on a fully digitised photogrammetric measuring system, has made a significant impact in the European market. It enables the control of the underground construction procedures such as tunnel excavation, contouring of the tunnel profile and the application of shotcrete lining as a primary support. It also allows a rough determination of the tunnel convergence; &bull A new deflectometer probe has been developed by Interfels for deviation measurements of horizontal and inclined boreholes. This probe has been successfully employed in surveying anchor boreholes, exploration boreholes in the face of advancing tunnels and in boreholes for ground freezing tunnels; &bull Real-time monitoring is being increasingly employed in the control of settlement sensitive tunnelling operations. Three types of automatic settlement monitoring instrumentation are used in Europe. These are motorised digital level, multipoint liquid level system and Electrolevel; &bull The Soilfrac grout compensation method has found widespread application in inner-city tunnelling beneath settlement sensitive buildings. A pre-condition for the employment of this method is real-time monitoring of settlement and heave; &bull The Integrated TBM Control System, proposed for the metro construction in Amsterdam, marks a peak In continuous efforts to achieve better control of tunnel construction procedures through geotechnical monitoring.