Northeast Boundary Tunnel Geotechnical Instrumentation and Condition Surveys

EBA provided geotechnical instrumentation and monitoring for the DC Clean Rivers Project, Division J, Northeast Boundary Tunnel (NEBT) in Washington, DC. The NEBT is about 27,000 feet long, 23 feet in diameter, and 60 to 140 feet below grade with seven new shafts.

EBA installed 221 borehole extensometers, 48 inclinometers, 34 observation or monitoring wells, 32 vibrating wire piezometers, 134 utility monitoring points, and a multitude of structural and ground monitoring points. The borehole instrument installation was completed over 3 years using multiple drilling crews. The borings for the geotechnical instrumentation extended up to 195 feet below grade.

Each borehole instrument was installed according to strict District of Columbia Department of Energy & Environment requirements to protect the groundwater resources and prevent aquifer contamination. The geotechnical instrumentation was mostly installed within the public right-of-way in a dense urban environment.

The EBA survey team performed daily manual survey monitoring using optical survey methods. EBA provided data for more than 900 manually surveyed instruments for more than 3 years.