Three Rivers Protection and Overflow Reduction Tunnel (3RPORT)

Case study narrative

Project narrative

In October 2014, 7NT personnel began the drilling of the Detailed Design Phase of the 3RPORT project as a part of the Design Team. The scope included two phases of work. The first phase consisted of 36 total borings: 20 shallow and 16 deep borings. The deep borings included six inclined borings approximately 20 degrees from vertical. The shallow borings were drilled to depths of 50 to 80 feet below ground surface, and the deep borings were drilled to approximately 250 to 330 feet below ground surface.

As part of the project, the City of Fort Wayne planned to construct a 60-foot by 120-foot Field Office Building that would serve as project offices for the duration of the large-scale tunneling and pump station project. At the conclusion of the project, the City would retain the building for use as an operations and maintenance building.

7NT provided geotechnical engineering services for this project. The planned space for the building inside the treatment plant facility consisted largely of trash and debris fill under six feet of engineered clay fill soils. The area had served as a dumping ground for decades prior. After initial discovery of the trash and debris fill, projections indicated a deep foundation system would be needed for the 7,200 square foot pre-engineered metal building facility. The extensive deep foundation system would cost $750,000 to $1,000,000 above the planned and expected cost of the facility.

7NT personnel worked with the City, Contractor, and other design engineers to determine an innovative and cost-effective solution so the structure could be completed within budget. 7NT engineers came up with a rammed aggregate pier solution to sufficiently stiffen the bearing soils to adequate capacity for the pre-engineered structure while also bridging the trash and debris soils to avoid future settlement and foundation-related issues.

The project was completed successfully under budget. 7NT personnel also oversaw construction activities of the building foundation and structure. Specifically, the 82 rammed aggregate piers, up to 40 feet in depth, were fully documented upon installation for compliance with project documents by 7NT personnel.

Scope of work

Technical scope