Monitoring SOE in Seattle
GEO-Instruments is monitoring the support of excavation system at 701 Dexter in Seattle. The deep excavation makes room for a 4-level underground parking garage that will be topped by a 10-story office building.
At the start of the project, the 701 Dexter building was still standing.
GEO used a drone to scout potential locations for the two AMTS that would monitor the excavation. The final locations are marked in blue and red above.
After the demolition, GEO installed the AMTS systems, a number of control points at stable locations outside the zone of influence, and road prisms on the streets. Above, the drone circles the rooftop AMTS.
The AMTS installed on the utility pole was powered by a solar panel. Both systems provided wireless reporting of data.
This drill rig is installing soldier piles around the perimeter of the excavation. As the piles were installed, GEO attached prisms to the top of every other pile. Additional prisms were installed on piles adjacent to the structure when the excavation depth reached 25 feet.
Prisms were installed toward the back of the piles to avoid problems from the installation of lagging.
The photo above shows sight-lines from the AMTS systems to monitoring points on the SOE and adjacent streets. As work progressed, a large dewatering pipe was positioned on top of the piles, blocking many of the prisms. These were moved to the front of the piles or to other suitable locations. Offsets were adjusted in software to provide seamless continuity of data.