Micropiles: Key To The Renovation Of The 161 First Street Building-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the redesign and construction of a foundation-support system for a Boston project. Existing perimeter walls were supported by deteriorating timber piles, with cracking observed during inspections. An initial helical-pile concept and a subsequent underpinning approach were set aside, in part because highly contaminated soil containing PCBs was found in the upper 10 feet of the basement. The project was shelved in March 2020 during the COVID-19 pandemic; updated owner requirements led to the final design using drilled micropiles (DMPs).<br /><br />Pile-load testing supported the design and helped achieve shorter micropiles. The presentation reports a target of twice dead load, or 320 kips, and compares initial, measured, and design bond values for alluvial sand, marine clay, and glacial till. A testing approach that extended a standard load test to higher loads contributed to pile lengths being reduced.<br /><br />Construction began in July 2022. Work included excavating to create sufficient headroom, drilling through contaminated soils, using a second rig, installing interior and exterior piles, managing wet drill spoils with a specialized system, and cutting and plating the piles before forming the foundation. The final pile was drilled on November 30.<br /><br />Key construction challenges included a small, restricted site, limited access and headroom, contaminated soils, and working in a basement described as “a bathtub.” The project relied on specialized drilling and spoils-management methods, along with daily coordination among the contractor and project teams.

Keywords

Boston foundation project

drilled micropiles

underpinning

contaminated soil

PCB contamination

pile-load testing

alluvial sand

marine clay

glacial till

construction challenges