Monitoring SOE at 701 Dexter

SOE at 701 Dexter

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.

AMTS on Rooftop

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.

AMTS mounted on Utility Pole

The AMTS installed on the utility pole was powered by a solar panel. Both systems provided wireless reporting of data.

Pile Driving Near AMTS

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.

Monitoirng Prism on Soldier Pile

Prisms were installed toward the back of the piles to avoid problems from the installation of lagging.


AMTS sight lines for monitoring SOE

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.