Providing Cutter Soil Mixing, CFA Piles and Dewatering at 200 Park Ave.

200 Park Ave is a 19-story tech-oriented office tower with four levels of underground parking located in San Jose, California’s urban core. Among the services provided were Ground Improvement Services (CSM [Cutter Soil Mixing], Soldier Beams, Tiebacks), Deep Foundation Services (CFA Piles [Augercast Piles], and Dewatering Services (Deep Wells and Water Treatment). Malcolm partnered with Brierley Associates for the design-build temporary shoring design and Middour Consulting for the design of the dewatering and depressurizations wells. Malcolm used two Bauer BG 42 with cutter soil mixing equipment set-ups to install a continuous CSM shoring wall around the perimeter up to 138-feet deep. The bottom two rows of tiebacks extended well below the static groundwater table, so tieback drilling and grouting methods were constantly evolved to handle the varying hydrostatic pressures that were encountered in the subgrade soils. Malcolm installed 253 each CFA hold down piles from the bottom of the excavation which allowed the project to stop the dewatering program at an earlier date, rather than waiting for the full building to be constructed. Due to the expedited schedule of this project, at certain points Malcolm had up to 4 separate crews deployed to the site working together towards the successful completion of the project.

To dewater this 55-foot-deep excavation, Malcolm installed eight deep wells up to 125-feet deep to draw the groundwater table down 40-feet and depressurize the deep aquifers beneath San Jose. Malcolm utilized a groundwater treatment system to discharge flows up to 300 GPM comprised of sand, carbon, and clay media to combat the different contaminants present in the groundwater that required to be treated prior to discharging to the storm drain under a NPDES permit.
To maintain an aggressive excavation schedule, Malcolm managed, pretreated, and disposed of trapped groundwater within the site as well as from the wells. Using the cutoff wall shoring method, Malcolm was able to achieve a flow rate of 30 GPM after a few months, allowing the site to gain more space.