Tunnel and Road Prisms

Bellevue Tunnel, WA.  The Bellevue tunnel was aligned with a major thoroughfare. To monitor possible settlements, GEO-Instruments installed borehole extensometers above the tunnel centerline and  arrays of road prisms across the road. Photo shows installation of a road prism.

Lid-Link in roadway

Borehole extensometers were terminated flush with the surface and LidLink antennas transmitted measurements to a GeoCloud server. This eliminated the need for cable trenches and curbside loggers. A road prism can be seen next to the LidLink.

Settlement and Tunnelling

This AMTS is monitoring road prisms and an UMP (utility monitoring point). Small settlements were detected as  the tunnel heading reached the location of each array, but stabilized within two weeks. A Lid-Link antenna for a borehole extensometer (BX) is circled.