Conditions at the site comprised of alluvial soils, extending to depths up to 160 ft, overlying bedrock of the Franciscan Complex. All shafts have been designed to develop their load bearing capacity both in end bearing and side friction in the bedrock only. The Franciscan Complex is composed of sandstone, shale, limestone, chert, serpentine, graywacke mixed in a seemingly chaotic manner. Engineering properties of the Franciscan vary significantly within limited vertical and horizontal intervals. Groundwater was encountered between 20 ft and 60 ft below working grade.
The shaft integrity was tested using Gamma-Gamma and CSL test methods, while visual inspection by the Mini SID camera ensured a clean base which was required for end bearing capacity. Malcolm Drilling employed synthetic slurry to stabilize the open rock socket to ensure compliance with the specifications through carefully controlled slurry exchange procedures. The concrete mix design was developed with a special emphasis on workability, which was needed for an extended period for the tremie concrete placement operation. The mix had the characteristics of self-consolidating concrete (SCC), with 50% of the Portland cement replaced by slag and fly ash.
This job was managed by
our Northern California Division
located in Hayward, California.
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