Tunnel Adit Fill Slide

Tunnel Adit Fill

Bethesda, Maryland

The Job

This tunnel adit fill project is part of the Purple Line project outside of Washington, DC. Specifically, the adit is located at the pedestrian connection between the Purple Line project and WMATA’s Bethesda station on the Red Line.

The Challenge

Plans call to connect the Purple Line to the Red Line using an adit constructed during the original construction of the Red Line. The adit is approximately 30 feet wide by a 35 foot tall arch. During preparation to blast from a shaft dropped adjacent to the station, a fault was identified passing through the adit.

The construction and design teams were concerned about stability of the adit during blasting operations as the Purple Line access tunnel was excavated towards it. The team determined that filling the adit to plug and stabilize it during blasting would be the most risk appropriate move.

Filling the adit would fulfill the design challenge of stabilizing the rock during blasting. However, it created the following challenges:

  • the tunnel adit fill material would need to be removed after blasting was completed
  • the adit is approximately 100 feet below grade
  • there is very limited space up top
  • material couldn’t segregate, and had to be pumped approximately 250 feet in addition to the 100 foot drop

The Solution

The tunnel engineer of record recommended CJGeo to the contractor. The EOR is familiar with CJGeo’s cellular concrete generation and placement expertise, and thought that cellular concrete would be the lowest risk way to fill the adit, while facilitating excavation and removal afterwards.

CJGeo took five days onsite to fill the adit, in lifts up to eight vertical feet. Due to the potential dead load from the rock cover, 400psi CJFill-Standard was the material of choice. By using our colloidal mixing dry batch process, the material set off quickly, ensuring that it would not consolidate during cure as lower energy mixing methods can suffer from.

Speak With An Expert

Facing a similar challenge to this tunnel adit fill project? Give us a shout or shoot us a text. Click the state marker for the location of your project for contact info for the appropriate rep.