Newport Tunnels: Soil Stabilization Project, Newport, Minnesota

Newport, Minnesota
2004

ECO designed and directed a pre-excavation soil grouting program in order to bore a 4.5 ft diameter tunnel below three railway tracks and fiber optic cables without causing settlement. A multiple hole grouting operation was conducted in the soil above the crown of the tunnel. The grouting program, which was performed by EJM Pipe Services Inc. and directed (in a hands-on capacity) by ECO, consisted of injecting a regular cement based suspension grout and sodium silicate based grout to stabilize the underlying soils below the tracks. The permeation grouting operation was monitored and assessed using the grouting instrumentation system, CAGES NS developed by ECO. An identical permeation grouting program was implemented under the same railway tracks and utilities a short distance away from this location. Both crossings were successful and no settlement was recorded. Major challenges on this project were the high silt content (more than 20%) and the limited cover (2 m) above the tunnel crown. It required 8 grouting passes, using the same sleeve pipes to obtain a continuous grouted soil conglomerate, whereby the steel sleeve pipes acted as forespiles (reinforced earth). There was absolutely no settlement during and after the tunneling operation.