Long-Distance Grouting, Materials and Methods

An abandoned 1600-meter (mile-long) rock tunnel had to be completely filled with grout. The total tunnel volume was approximately 4500 cubic meters (6000 cubic yards). The tunnel was water-filled with access only at each end through narrow, 25-meter deep (80 ft), vertical shafts. Access for pumping was feasible only from one end of the tunnel, thereby requiring unusually long distances for pumping. Through an extensive laboratory testing and modeling program, different grouts were tested for suitability for this project. The ideal grout would have low viscosity, good stability and, after setting, low bleed, moderate strength and low permeability. Materials tested included cement-bentonite, cement-flyash and combinations including blast furnace slag cement. Data is presented on the various grout materials leading up to the choice of a cement-bentonite-slag cement blend as the optimal mix for the project. The unusual conditions at this project required the use of divers and remote-operated vehicles to inspect the tunnel and to place the initial cable that would allow grout pipes to be drawn into the tunnel. Each component of the grout system was engineered to provide adequate capacity to fill the tunnel in three to four days, working around the clock. A backup system using a sleeve pipe to provide secondary grout was devised and installed. The work in the field progressed more or less as planned, with a few unknowns cropping up to make for some difficult moments. As it turned out, the secondary grout line was necessary to complete the work. Grout samples were taken during the project for confirmation testing and borings were drilled into the tunnel after the work to verify that the tunnel was full. Data from this phase of the project are also presented. This project presented an unusual opportunity to plan and test components pre-construction. White there is no way to verify, the distances that the grout was pumped may represent some kind of record.