New York’s Greatest Engineering Job
By Gerard Hillenbrand, P.E.
That was the subject of Met Section’s Joint Meeting held Tuesday, November 15th 2005 at Con Edison’s headquarters in Manhattan. More specifically, the subject concentrated on the design and construction of our city’s water tunnel #3 as well as Con Edison’s Steam Tunnel. Con-Sponsors for this meeting, with approximately 60 engineers in attendance, included the Power Engineering and Industry Applications Society of IEEE and the Edison Engineering Society. The subject matter of this meeting qualified for on Professional Development Hour of credit toward the continuing education requirements recently mandated by the N.Y. State Department of Education.
This meeting’s speakers were Lou Huang, P.E., and Chief of Waterworks Construction for N.Y. City’s Bureau of Environmental Engineering and Anthony Del Vescovo, Director of Tunnel Operations for the Schiavone Construction Company. Mr. Huang began his slide presentation with an overview of our city’s world renowned water system, which about 1.2 billion gallons of potable water to over 8 million city residents and 1 million upstate residents every day. This water, which is generally considered to be the world’s standard for tastefulness and purity, is supplied from a network of reservoirs and lakes located in a 2000 square mile watershed extending 125 miles north and west of N.Y. city. The Catskill and Delaware River Watersheds are located on the west side of the Hudson Rivera and supply about 40% and 55% of our city’s water, respectively. The Croton Watershed, located North of N.Y. city on the east side of the Hudson River, collects about 5% of our water and feeds this water into the Kensico Reservoir at the southern end of the Croton Watershed. The water collected in these Catskill and Delaware watersheds is transported via aqueducts and tunnels in upstate New York under the Hudson River and through the Croton Watershed into the Hillview Reservoir located in Yonkers just north of the N.Y. city line. The New Croton Aqueduct and Tunnel feeding into the Jerome Park Reservoir located in the Northern Bronx, and completed in 1970 supplement this supply system.
Within N.Y. City the water is distributed to buildings through a series of deep tunnels and water mains located just below street level. These deep tunnels are more efficient in distributing water since they provide mush greater capacity (about 24 times the volume of the average water main), can withstand much higher pressures, and are much less disruptive to busy city life. Our city has three basic tunnel systems. Tunnel No. 1, completed in 1918, runs from Hillview Reservoir south through the Central Bronx, under the Harlem River, down the west side of Manhattan, under the East River, and into Western Brooklyn. Tunnel No. 2, completed in 1936, runs from Hillview Reservoir through the East Bronx, under the East River into Whitestone, Queens, then parallel to the East River into the Red Hook section of Brooklyn where it connects to the terminus of Tunnel No.1. The Richmond Tunnel connects this terminus with Staten Island via a major excavation under New York Harbor.
City Tunnel No. 3, currently under construction, is the largest capital project in our city’s history and will extend more than 60 miles and scheduled for completion in 2020. Stage 1 of this tunnel No. 3 was completed in 1998, is now in operation and runs 13 miles from Hillview Reservoir, southward through the Bronx, under the Harlem River into upper Manhattan, down the west side into Central Park, turns east under the east river and Roosevelt Island into Astoria, Queens. Stage 2 of tunnel No. 3, now being worked on, consists of an eastern section 10.5 miles long running from Astoria to Red Hook Brooklyn scheduled for completion in 2009, and a Manhattan section 8.5 miles long running south into the East Village and looping north in a 13 mile path to reconnect into stage 1 and scheduled for completion in 2012. There are no current plans to extend tunnel no. 3 into Eastern Brooklyn and Queens. Total projected cost of tunnel no. 3 is $6.0 billion and, when complete, will provide for inspection and repair of city tunnels no. 1 and no. 2 and for rehabilitation of their interconnected conduits.
The various components of stage 2 of tunnel no. 3 currently nearing completion, at a total cost of $2.8 billion, consist of the eastern section in which the access shafts (1 in Queens and 4 in Brooklyn) and tunnel are finished, and the Manhattan section in which tunneling and access shaft drilling are currently being done. The tunnels vary in diameter between 10 and 12 feet and are bored between 500 and 800 feet below ground level as determined by local geological conditions. Access requirements and difficulty of equipment delivery and ease of excavation removal determine the exact route of the tunnels. The total length of the stage 2 tunneling is 32 miles with vertical access shafts located approximately every 2000 feet. Geological conditions for uniformly monolithic rock formations are usually a the 700 to 800 foot level and this depth provides a 200 foot buffer zone of solid rock above the tunnels, thus providing seismic protections and safety from nuclear blasts. The tunnel system is subjected to various pressure zones. For example, the east side of Manhattan has ten times the average water consumption of some other sections of the city, and all tunnels must be designed to withstand the maximum pressures and flow volumes.
Mr. Del Vescovo’s slide presentation concentrated on the specific details of tunneling operations. Tunnel Boring Machines (TBMs) can be as long as 200 feet and must be lowered disassembled through the access shafts and then reassembled on the tunnel floor. A typical TBM has a cutter head diameter of 12 ft 7 inches, consisting of 27 individual rotating cutters of 17-inch diameter. A typical cutting stroke is 5 feet and the cutting mechanism itself can extend 75 feet behind the cutting head. The accompanying electrical, compressed air, communication and conveying equipment can extend the total TBM machine length to 200 feet. A typical TBM is rated at 1800 horsepower and operates at 575 volts. Electrical supply on the surface is 13,800 volts and multiple conduits distribute this power down the access shaft, into the tunnel and then to the TBM and its auxiliary equipment. The TBM can be mounted on rails and moved by a locomotive. Tunnel boring progress varies between 50 and 150 feet per day depending on geological conditions and operational circumstances. Placing explosives into drilled holes in the tunnel face and detonating can assist tunnel boring. Blasts are limited to one per day and average 10 feet in tunnel progress. The rough tunnel wall generated by the TBM is stabilized by a combination of circular metal collars, strips bolted into the wall and supporting wire mesh, and freeze pipes next to the wall through which low-temperature brine is circulated from a generating plant located above ground.
As previously described, the Manhattan section of stage 2 of tunnel no. 3 is currently the site of the most aggressive construction. Phase 1 of this effort into the east village involved excavations of 600 depth and tunnels 18,721 feet long. Phase 2 (The Hook-Shaped or Horseshoe shaped extension to the North begun in January, 2005) is projected to be 14.143 ft. long with 9 vertical access shafts in congested Manhattan. This 4-yeat phase 2 extensions are in areas where solid rock is unearthed 70 to 110 feet below ground surface. Typical vertical access shafts resemble an inverted cone gradually increasing in diameter when approaching the surface. These shafts are topped out with a valve chamber and a distribution chamber (just below surface level) with connections to the water mains. These valve and distribution chambers may be as tall as 200 ft. and connect at their lower ends to riser elements lining the vertical shaft and locating the stainless steel piping covering the conduits for electrical, compressed air, and communication equipment. Excavated material is conveyed to the surface via vertical conveyor belt systems moving at speeds approaching 500 ft. per minute. To complete water tunnel #3 additional design and planning work is currently being engineered. This work includes stage 3 which consists of another tunnel from Kensico Reservoir into Manhattan and stage 4 which includes a valve chamber for controlling water flow from Bronx to Queens, all scheduled for completion by 2020. Also, the federal environmental protection agency has mandated the construction of a filtration planted located at exit of the Croton system enhancing water purity using ultraviolet techniques to reduce and more accurately monitor such contaminants such as Chlorides, Fluorides, Phosphates, and Nitrates as well as poisonous trace metals such as lead and copper.
The construction of Con Edison Steam Tunnels is similar to the procedures described above except smaller in scale, smaller diameter and depth. Construction currently nearing completion is 6 miles of tunnel length with 8 access shafts, 5 of which are complete. This meeting concludes with the usually informative question and answer period and is typical of the intellectually challenging subject mater met section plans to present to its members. We look forward to seeing you at our next meeting.