DC Water initiated the construction of the Northeast Boundary Tunnel (NEBT) to connect with the existing Washington DC sewer system. The intention of the project is to mitigate sewer flooding associated with substantial population growth over the past century, thereby improving the water quality of the Anacostia River.
Crux performed a first phase of work for Soilfreeze, Inc. in 2019, installing 39 permanent horizontal casings to support future ground freezing prior to tunnel construction, and returned to the project to install an additional 14 casings for Keller Group in 2021.
A modified mud rotary tooling and approach was used to permanently install HWT casing to designed lengths, which ranged from 55 to 100 feet. Crux’s specialty track drills were lowered to between 75 and 100 feet below ground level by crane into multiple 26-foot diameter shafts to complete installations. These drills were specifically designed to work safely and productively in congested areas.
Project challenges included drilling horizontally below the water table in soft material. Crux has experience in these conditions, and worked with the client and owner in advance to establish the appropriate equipment and procedures for a successful project outcome. The Crux team fabricated drill-through diverters that allowed the permanent casing to be installed without causing large inflows of fluids or solids to the shaft. Additional challenges included transporting equipment to the entry shaft through densely populated neighborhoods and working on a site congested with contractors. Crux ensured a heightened focus on communication with all contractors onsite to maintain a safe working environment.