Challenges of Building the Deepest Basement in Downtown San Jose

This paper discusses the challenges associated with the design and construction of a deep basement in downtown San Jose, California for the 200 Park Avenue project. The aim is to present the critical design issues, how the challenges were addressed, details of the selected shoring design, and the performance of the shoring system during construction. The critical design issues that will be discussed related to retaining the deep excavation and constructing the basement include shallow groundwater, artesian pressures, settlement outside of the excavation, shoring earth pressures, and shoring wall movement. Subsequently, the paper will describe why a tied-back cutter soil mix (CSM) cutoff wall was selected as the shoring system and how it addressed the critical design issues. The design of the tied-back cutoff wall will also be discussed. Lastly, the performance of the tied-back cutoff wall during dewatering and excavation and how it compared to the design will be included. The performance was measured through a monitoring program, including survey data points and piezometers.