Design and impact of the Beacon Hill Station exploratory shaft program

To help reduce construction risks for the up-coming Beacon Hill Tunnels & Station contract, the project Owner, Seattle's Sound Transit, made a decision to construct a test shaft into main soil strata at the location of the future Beacon Hill Station. In addition to evaluating the performance of the ground from the point of the station constructibility using the Sequential Excavation Method (SEM), the construction of this shaft provided an opportunity to evaluate the numerical modeling approach used in the design of the station excavation, prior to the start of the station construction. Observations made during the test program resulted in a fundamental change in the selected construction methodology of the station shafts. The results also indicate that it is feasible to use 3-dimensional structural analysis to predict behavior of SEM-constructed shafts in soft ground.