Merrill Gardens at Hillsboro

Client: Pillar Properties

Year: 2018 - 2024

Location: Hillsboro, Oregon

Features:

  • Geotechnical borings and Cone Penetrometer Testing (CPT)

  • Installation of groundwater observation wells and infiltration testing

  • Deep foundation and pavement recommendations

  • Site-specific seismic response analysis

  • Construction observation services during earthwork

Project Summary

Merrill Gardens at Hillsboro is an 8-story mixed-use development that includes assisted-living spaces, a medical clinic, and retail opportunities. As the tallest building ever planned in downtown Hillsboro, this project presented unique geotechnical challenges, particularly related to soft soils and high groundwater levels. Central Engineering Services conducted a comprehensive geotechnical investigation and site-specific response analysis to support the project design and construction. Through ongoing collaboration with the project team, Central provided solutions to overcome significant geotechnical hurdles, ensuring a stable and resilient foundation system.

Scope of Work

Central Engineering Services performed an extensive multi-phased geotechnical investigation for Merrill Gardens, including geotechnical borings, cone penetrometer testing, and infiltration testing. The team installed groundwater observation wells to monitor site conditions and provided deep foundation recommendations. A thorough site-specific seismic response analysis was conducted to support structural design. Central also offered consultation throughout the design phase and construction observation services during the earthwork portion of the project.

Features

  • Conducted CPT testing and solid-stem auger boreholes to collect disturbed and in-situ soil samples for analysis

  • Collaborated with KPFF to develop a cost-effective hybrid wall and backfill-supported "bathtub" slab design

  • Installed piezometer-based monitoring wells to continuously monitor groundwater conditions

  • Provided recommendations and support for an extensive dewatering program involving over 50 drilled wells and a Baker tank system

  • Issued six technical memorandums to address evolving design considerations and construction challenges

  • Monitored and analyzed settlement data to ensure long-term stability of the structure

Results

Central Engineerings comprehensive geotechnical analysis and proactive involvement helped mitigate the complex geotechnical challenges of the site. The successful implementation of the dewatering program and excavation strategies allowed for the construction of a stable subgrade and the eventual pour of the structure's slab. Continuous monitoring and technical guidance provided peace of mind to the project stakeholders, ensuring long-term performance and safety of the development.