When a 42″ MTBM stopped advancing under the shoulder of I-75 in Miami, Florida, the tunneling contractor had to sink a shaft adjacent to the roadway, and then hand mine in to recover the machine.
The MTBM was stalled approximately four feet from where the recover shaft was sunk. The face of the machine was under the shoulder, and tail of the machine was under the outside lane of the interstate. The machine was approximately 15′ below ground water level, and there was extensive ground water infiltration into the sheet pile rescue shaft.
In order to ensure that the ground would be stable to facilitate hand mining in from the shaft while avoiding settlement of the interstate, the tunneling contractor reached out to CJGeo about increasing the stability of the soils.
While the desire was to increase the stability of the soils, the treated soils needed to be hand excavatable by divers working in a casing slightly larger than the MTBM. Soils in the desired treatment zone included lime rock, course sands and silty sands.
CJGeo determined that acrylic grout would be the most appropriate to bind the soils together, significantly reduce their permeability, but still facilitate hand excavation in an underwater confined space.
Because the failure mechanism of the MTBM was unknown, CJGeo grouted the zone between the MTBM face and the rescue shaft, then grouted a collar around the entire MTBM machine in case the machine needed to be completely uncovered.
CJGeo successfully performed the permeation grouting, then divers excavated back to the machine, freeing it. The grouted face held once the receiving ring was installed and the sheet pile wall cut, and was easily excavatable for the divers.
In addition to grouting the soils, CJGeo’s crew also performed grouting of numerous nuisance ground water leaks through various joints in the sheet pile shaft.