Adjacent tunnel and loading dock projects To complete this excavation, a retention system needed to be designed to allow up to a 30 ft (9 m) deep excavation along the operating hospital, road and existing tunnels, and to allow all vehicle and pedestrian traffic access to the Mayo facilities while handling the geotechnical and geometric constraints. much faster than cased excavation. To monitor noise and vibration that might have an impact on the adjacent Jacobson building, where doctors perform intensive robotic surgery, vibration monitors were set up outside and inside of the building. Crews worked with hospital staff to ensure levels were not exceeded and all drilling activities were arranged around the surgery schedule. The predrilling and resonancefree side grip Movax were able to eliminate vibration impacts to the project. The general contractor requested that trumpets were used wherever possible to limit the waler protrusions into the excavation. The predrilling information was invaluable to confirm anchor elevation as adjustments were extremely difficult because each beam needed to be prefabricated offsite and then delivered to the project. The tiebacks were installed with a Comacchio MC15 drill rig. An injection bored anchor was selected with a larger top hammer as it allowed for quick installation in the overburdened soils but could also penetrate the limestone. Utilizing a larger rig proved to be impractical due to numerous overhanging utilities and the narrow width of the excavation. Additional Challenges The design also had to incorporate egress for both vehicle and pedestrian traffic adjacent to and over the excavation requiring multiple bridges to be utilized, access for delivery and service vehicle traffic, the support of existing utilities, support of the existing pedestrian tunnels, and underpinning of the existing structures. 16 * DEEP FOUNDATIONS * JAN/FEB 2023 Numerous utilities were supported during excavation