The Job
This project involved constructing a new sewer outfall pipe in Atlanta, Georgia. The alignment required trenchless installation beneath Galleria Drive. Reynolds Construction served as the tunneling contractor for the Cobb County-Marietta Water Authority. The tunnel was an 84-inch diameter hand-mined liner plate structure and spanned approximately 480 feet in length. The new carrier pipe inside the tunnel was a 30-inch sewer line.
The Challenge
Hand-mined tunnels through rock often require high-strength grout. In this case, the specification called for a 60 lb/cu ft grout with 400 psi compressive strength. A grout of that density can create buoyancy problems. Additionally, multiple consecutive lifts would have been required, adding unnecessary risk to the project. The large volume of the annulus also meant that using 60 lb/cu ft material would drive up material costs.
The Solution
CJGeo recommended using a 45 lb/cu ft density mix instead. CJFill-Standard cellular grout was lighter and still met the strength requirement while offering better buoyancy control and faster production rates. The team utilized a high-energy mixing mobile batch plant for onsite generation. We used CJFill-Standard cellular grout for the application.
The operation required 622 cubic yards of cellular concrete. The crew placed this volume in two lifts over the course of just two days. This method successfully encapsulated the new carrier pipe and the pipe remained perfectly on grade without any flotation.
Speak With An Expert
Facing a complex tunnel backfill challenge? CJGeo provides engineered cellular concrete solutions for tunnels and annular spaces nationwide.
