Challenges of Building the Deepest Basement in Downtown San Jose-Video

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The 200 Park Avenue project in downtown San Jose involved a 19-story office building with four basement levels, requiring an excavation 54–58 feet deep. Key challenges included limiting movement near neighboring buildings and utilities, managing shallow groundwater, and preventing heave from artesian pressure in a deep sand layer.<br /><br />The team selected a stiff, 39-inch-thick cutter soil mix wall, extending 135–140 feet to cut off the sand layers. Four levels of tiebacks supported the wall. Dewatering lowered groundwater inside the excavation while limiting drawdown outside; wells also depressurized the artesian layer to maintain an adequate safety factor against heave.<br /><br />Monitoring during construction showed the system performed as designed. Groundwater outside the excavation dropped only slightly, wall deflections were generally around half an inch, and settlements were minor. The excavation remained dry and stable, allowing the mat foundation and waterproofing to proceed. The project’s success depended on close collaboration among the design and construction teams.

Keywords

200 Park Avenue

San Jose excavation

cutter soil mix wall

dewatering system

artesian pressure control

deep foundation excavation