City slickers: SF drilling in the rain

In March 2023, Pitcher Services completed four solid-flight auger and mud rotary combination borings ranging in depth from 30-175ft for this project. Initially, Pitcher used the solid-flight auger to drill until groundwater was encountered and then set casing and switched to mud rotary drilling to the final depth. Sampling was every 5ft using drive samplers (SPT, Mod Cal and Shelby Tubes). Downhole suspension logging was performed in the deep borehole to 175ft. Pitcher also installed two 2″ standpipe piezometers to 30ft in depth. All drill spoils were contained in 55-gallon drums and transported to the staging area for further analysis.

Highlights:

• Soil sampling (SPT, Mod Cal & Shelby tube)
• Combination of auger and rotary methods
• Downhole suspension logging
• Contract value $45k

Challenges/Benefits:

• Difficult and tight access locations in downtown San Francisco
• Many underground utilities checked with air-knife to clear borings to 5ft ahead of drilling activities

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