technologyprofile

High-precision deformation monitoring plays a critical role in New York subway construction project. Transporting six million passengers each year through million improvement program for the South Ferry Terminal. The effort will result in the relocation of the South Ferry subway station in New York City the station platform and mezzanine to a new loca- could be a lot easier. tion beneath Peter Minuit Plaza and State Street at the foot of Manhattan. The rebuilt station will The station, situated at the tip of Manhattan, adja- incorporate a number of improvements, including cent to the Staten Island Ferry terminal and Battery a full-length platform that can accommodate two Park, was originally built in 1905 when subway 10-car trains, additional station entrances and sta- trains were much shorter than today’s models. Its tion accessibility compliant with the Americans platform can only accommodate the first five cars with Disabilities Act. The new terminal will have of each train. Disembarking passengers must walk the ability to handle up to 24 trains per hour. forward from the rear cars to exit, which causes The construction work is being done under a delays. Unlike most modern stations, which have design-build contract by Schiavone Construction two or three tracks, the South Ferry terminal has Company of Secaucus, N.J., and includes strength- only a single track, and the sharp curvature of the ening and stabilizing the of the exist- platform and track slows train operation and gener- ing structure using the mini-pile founda- ates excessive noise. In addition, the single entrance tion technique and -and-cover excavation (a and narrow stairs can cause congestion, and do not method of construction for shallow where provide easy access for disabled passengers. a is excavated and roofed over) of a new To remedy these limitations, the New York tunnel. Underpinning stabilization and excavation Metropolitan Transit Authority launched a $400 work commenced in 2005; the project is expected to be completed by the end of 2007. It was clear from the outset of the project that a rigorous deformation monitoring regi- men would be required to protect nearby historic structures. To support this phase, Schiavone looked to high-precision total station technology.

Existing South Ferry Station

A Leica Geosystems A Rigorous Monitoring Regimen robotic total sta- Schiavone contracted with Mueser tion is mounted on Rutledge Consulting Engineers (MRCE) one of the tunnel’s and Geocomp Corporation, both of New sidewalls; clearance York, to provide specialized geotechnical between the train design and monitoring services for the and sidewall is less underpinning and tunnel construction of than 18 inches. the new South Ferry subway station.

Reprinted with permission from POB Magazine. Copyright March 2007. technologyprofile Geodetic Monitoring technologyprofile The monitoring of construction objects and dangerous areas is becoming more and more important. Monitoring involves periodically and automatically measuring reference points in or around the active area to determine deformation. When movement tolerances are exceeded, it is often necessary to time, a user can log onto the iSiteCentral website and see a Benefits of Automated Monitoring Systems immediately analyze the measured data to activate response status report on the condition of every sensor on the site and “An effective performance monitoring system can play a major role events. Monitoring tasks and deformation analysis present examine graphs showing the complete history of data for the in controlling costs on a large infrastructure construction job,” Marr some of the most sophisticated challenges in the sensor or group of sensors. says. “The monitoring system can reveal potential problems and profession today because they require the highest accuracy, “The project presents unique challenges for monitoring deficiencies in time for corrective action to be taken. It can reduce “The monitoring regimen developed for this project focuses maximum reliability of the sensors, automatic measurements, implementation and logistics,” Marr says. “For example, the the possibility that construction will adversely affect neighboring on the existing tunnels and nearby structures, including some and highly flexible computation and analysis tools. existing tunnels need to be monitored before excavation begins people and facilities, and also reduce possibilities for claims arising very important historic buildings and facilities within Battery Leica GeoMoS is an open, scalable and customizable soft- to collect baseline data. This means that nearly all of the instru- from construction-related damage.” Park,” says W. Allen Marr, CEO of Geocomp. “Movement toler- ware suitable for a wide range of monitoring applications. All mentation has to be installed inside the active subway tunnels. “In this instance,” Nyren adds, “the vibration monitoring led ances for this job are fractions of measurement and result data are stored These tunnels are normally in operation 24/7—even during the Schiavone to change their blasting practices in the underlying an inch. This meant we needed in an SQL database so it can be accessed construction—which limits access to the tunnels to once every rock. The vibrations were exceeding the project thresholds, and the the most reliable, rugged and and configured from anywhere in the few weeks. For that reason, it is necessary to create a system robotic total stations showed that very little deflection occurred in repeatable measuring systems.” world. Data can be exported to other sys- that will operate reliably and automatically around the clock nearly all of the tunnel sections affected by construction.” The monitoring solution tems in ASCII, SQL, DXF and BMP formats. under the most difficult environmental conditions.” Precise deformation monitoring is increasingly becoming a delivered by Geocomp and A wide range of sensor types are “The wireless component was a very desirable factor,” standard requirement for major engineering projects, especially MRCE uses 10 Leica Geosystems supported, and additional sensors can adds Rob Nyren, the Geocomp instrumentation engineer. those involving underground excavations, to protect nearby (Norcross, Ga.) TCRP1201 auto- easily be added. Combining data from “However, in active tunnels, wireless communication is a structures from damage during the construction process. More matic robotic total stations, a range of geodetic and geotechnical challenge even in the best conditions. New technologies like importantly, it provides a critical margin of safety for workers which monitor more than 450 sensors helps to ensure the lowest pos- spread-spectrum radios with powerful transmission capabili- on the job as as people going about their daily business in prisms across the site. Inside sible risk. For combined GPS/total sta- ties allowed us to overcome many of the obstacles. By going the vicinity of the excavation. the tunnel, the total stations tion monitoring systems, GeoMoS can wireless, we avoid installing several thousands of feet of are mounted on brackets on be used with Leica GPS Spider reference cabling for sensors, communication lines, etc., and save both Manufacturer Information: the tunnel walls, hanging from station software for advanced GPS mon- time and extra union labor costs.” Leica Geosystems, www.leica-geosystems.com the tunnel ceilings near cross- itoring using GNSS technology. Sensors overs, between structural col- and measurements are automatically umns in stations and on “crash controlled over cable, radio LAN, WLAN walls” between opposing direc- and GSM communications. Connection tion tracks. The prisms are of the different sensors, such as GPS, affixed to the walls near the total stations and levels, is handled by concrete anchors every 10 ft a Leica Sensor Manager component. along the length of the tunnel It also provides an interface for sensor near the construction work to configuration. GeoMoS features real- detect absolute and differential time data synchronization and security movements of the walls during between client and server using stan- excavation and underpinning. dard data transaction technologies. Above ground, the total sta- The software consists of two main tions are mounted on buildings applications: Monitor and Analyzer. The online function, with monitoring prisms affixed to building structures, as well Monitor, is responsible for sensor control, collection of data as the walls that support the cut-and-cover excavation. and event management; Analyzer is in charge of analyzing The robotic total stations are controlled and synchronized and reporting the measured data, plus editing and post-pro- using Leica GeoMos monitoring software. Two local computers cessing where required. in the tunnels communicate via wireless radio links to the total stations. The computers are remotely accessible via IP-enabled A Web of Wireless Data phones for data retrieval from GeoMos. All monitoring data from the site—from the robotic total In addition to the Leica automatic total station network, stations and the additional instrumentation—was transmit- MRCE and Geocomp also deployed an array of other instru- ted to Geocomp’s Web-based iSiteCentral monitoring and mentation. Seismographs installed both inside the tunnels reporting system. Authorized project users could access the and affixed to the foundations of nearby structures record monitoring data from iSiteCentral via password-controlled vibrations caused by construction activities. Tiltmeters on the Internet portal in real-time 24/7 using a landline, RS232 external walls of the exposed tunnels monitor any twist of the serial port, mobile telephone or satellite connection. The tunnel structure while they are undermined. And in-place incli- iSiteCentral system can provide immediate notification of nometers installed in the support-of-excavation walls and in potential issues by mobile phone, E-mail or pager whenever the ground in front of nearby historic structures monitor lateral out-of-tolerance conditions are detected. This way, problems deflections during excavation. can be addressed before they become critical. At any given Americas Leica Geosystems Inc. Norcross, Georgia 1-800-367-9453 www.leica-geosystems.com.us