Jones Pavilion Service Tunnel, Virginia Mason Medical Center
The goal of the service tunnel project is to provide a below-gradelink between the Jones Pavilion Building and a service corridor of the hospital. The finished dimensions are approximately 8’ wide by 8’ high by 80’ in length. The tunnel first cuts through an existing foundation wall of Jones Pavilion, mines under the foundation wall of Central Pavilion, runs parallel to an existing foundation wall, and extends below and between a series of foundation footings from the Central Pavilion Building. The tunnel also extends under the an existing Hyperbaric Chamber floor and continues to penetrate the existing concrete wall at the west end to emerge into the service corridor of the Central Pavilion Building. CivilTech designed the tunnel shoring system and final tunnel structure. The shoringsystem was designed based on sequential excavation method, which included the use of steel ribs and steel liner plates. Our engineers adopted a soil nailing and shotcrete wall system, along with roof and wall spiling to help control potential ground loss which could cause excessive differential settlement of the existing footings. The design team determined that the maximum allowable differential settlement between the footings cannot be more than 0.5” or the building will suffer structural damage. Thus, a rigorous monitoring program was developed and incorporated as part of the mining operation to ensure the differential settlement threshold was not exceeded. A “finite difference” program (FLAC) was utilized to analyze for soil-structure interaction and to determine design loads for both the temporary shoring system and final tunnel structure.