Specialty geotechnical contractor Moretrench is the first recipient of the Innovations in Ground Improvement Award, which was presented during the Colorado School of Mines annual short course on Ground Improvement in Underground Construction and Mining, held in Golden, CO from May 18th to May 20th, 2015. According to Course Director Levent Ozdemir, Ph.D., P.E., the newly minted award is given for the development of innovative solutions, products or design to ground improvement in underground construction or mining. Moretrench was selected for its work on the Northern Boulevard Crossing in Queens, New York, the 2nd Avenue project in Manhattan, New York, and the Port of Miami Tunnel project in Florida.
“Each of these projects presented different tunneling challenges,” notes Moretrench Vice President of Engineering Paul Schmall. “Northern Boulevard was an SEM tunnel through difficult, complex soils deep below the groundwater table. 2nd Avenue was an unanticipated stretch of mixed faced conditions in a primarily rock tunnel. And the Port of Miami involved mining of two cross passages between 80 and 120 feet below sea level and situated mostly within a highly pervious coralline rock formation.”
While ground freezing was used on all three projects, there were markedly different considerations that had to be addressed. At Northern Boulevard, where the tunnel alignment passed directly beneath an active subway box and an elevated rail track, carefully performed heave and settlement control measures during growth of the freeze and the subsequent thaw period were critical to maintain the integrity of the structures. Congested above-ground conditions and traffic along 2nd Avenue meant that the work had to be accomplished from two small access areas, using angled drilling and freeze pipe installation. The Port of Miami cross passages were mined through a circular frozen zone created by means of horizontally-installed freeze pipes– a first in North America. Here, the potential for moving groundwater, which hinders freeze closure, was addressed by grouting to reduce the permeability of the coralline formation ahead of Moretrench’s work. But with the cross passage alignment deep inside the eastbound tunnel, the main components of the ground freezing system had to be located and maintained above ground, almost half a mile from the work zone. Contact cooling systems were also critical to ensure continuity of the freeze along the entire length of the tunnels.
For further information on the projects cited in the award, see this recent Tunnel Business Magazine article, and also visit our website Resources ground freezing section for more project case studies.