DEFORMATION MONITORING SYSTEM FOR NEW YORK SUBWAY CONSTRUCTION PROJECT USES SURVEYING TECHNOLOGY FROM LEICA GEOSYSTEMS
The $400 million South Ferry Terminal improvement program involves a major upgrade of the existing station, which is located underneath Peter Minuit Plaza in Lower Manhattan, adjacent to Battery Park and the Staten Island Ferry Terminal. The work is being done under a design-build contract by Schiavone Construction Company of New Jersey, and includes underpinning of the existing tunnels using mini-piles and cut-and-cover excavation of a new tunnel. Schiavone contracted with Mueser Rutledge Consulting Engineers (MRCE) and Geocomp Corporation to provide specialty geotechnical design and monitoring services for the underpinning and tunnel construction.
The monitoring system developed by Geocomp and MRCE includes 10 Leica TCRP1201 total stations, monitoring more than 450 prisms above and below ground. The system also includes seismographs inside the tunnels to record vibrations, tiltmeters on selected structures to monitor deflection, and inclinometers installed in the support-of-excavation walls and in the ground in front of nearby historic structures to monitor lateral deflections.
The Leica TCRP1201 robotic total stations, permanently mounted at fixed locations, take continuous laser measurements to prisms mounted on buildings and other structures on the surface within a several-block radius of the worksite. Other TCRP1201 total stations are performing the same function underground, taking precise measurements to prisms attached to the tunnel walls. The automatic monitoring system alerts authorities to any out-of-tolerance movements that could pose a danger to the buildings or workers above and below ground. All 10 total stations are controlled and synchronized using Leica GeoMoS monitoring software.
"The monitoring regime developed for this project focuses on the existing tunnels and nearby structures, including some very important historic buildings and facilities within Battery Park," said W. Allen Marr, CEO of Geocomp. "The project presented unique challenges for monitoring implementation and logistics. The existing tunnels are being kept in operation during the construction, which limits access to the tunnels to once every few weeks. Movement tolerances are fractions of an inch. These conditions demanded we use the most reliable, rugged and repeatable measuring systems."
Because of the limited access to the monitored locations, Geocomp deployed a wireless monitoring system for remote access and automated data transfer to a Web-based monitoring and reporting system. Data is available 24/7 via a secure real-time Internet link using Geocomp's iSiteCentralÃ system.
"Precise deformation monitoring is increasingly becoming a standard requirement for major engineering projects, especially those involving underground excavations, to protect nearby structures from damage during the construction process," said Gerard Manley, vice president of engineered solutions for Leica Geosystems. "More importantly, it provides a critical margin of safety for workers on the job, as well as people going about their daily business in the vicinity of the excavation. We are very pleased that we can play a role in being a good neighbor to the members of the community affected by the construction project."
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