Tunnel Business Magazine

APR 2018

TBM: Tunnel Business Magazine is the market leader for North America. TBM is written for leading professionals in all aspects of tunneling and covers project stories, design elements, contracting strategies, legal issues, new technology and more.

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TUNNELINGONLINE.COM F E A T U R E S T O RY 4 3 TBM: TUNNEL BUSINESS MAGAZINE // APRIL 2018 frequently requires extensive replacement and upgrades ex- tending far beyond the excavation site when these utilities are disturbed. The costs stemming from these risks and utility impacts are sometimes so great they may offset the costs as- sociated with the additional excavation associated with the single-bore method. Because there is limited business disrup- tion, there is little need to establish business subsidies during construction. (L A had to establish a Business Interruption Fund for the Crenshaw/LAX Transit Project.) Streetscape – Conventional cut-and-cover subway stations typically have relatively narrow stairway/escalator passages located on the sidewalk leading to the ticketing mezzanine below the roadway. This arrangement compromises the side- walk width and generally degrades the streetscape. Unless these facilities are enclosed with lockable head houses, these areas attract unwanted activities during off hours. Because the single-bore method constructs all the ticketing facilities off-street behind the sidewalk, the sidewalk width is not im- paired and the ticketing hall can be fully enclosed and secured in the same way as any other building in the downtown core. Joint Development – The single-bore method has signifi- cant potential for joint development in the downtown core because all transit-related facilities are contained in a base- ment-like structure. This leaves a substantial area on the first floor and the full area on the floors above available for additional public or private-sector development. This is dou- bly valuable as the ticketing hall facility can itself become a downtown destination, not merely a point of transit to other destinations. Safety – The single-bore method also has safety advantages over conventional cut-and-cover methods. Because the entire ticketing hall is maintained as a place of safety, evacuation from a train fire is simplified. Passengers reach the point of safety as soon as they leave the back of the boarding platform. Also, since the running tunnels are constructed in separate chambers, pas- sengers who are evacuating the train mid-tunnel can reach the non-incident tunnel through frequently spaced fire doors. A PROMISING FUTURE FOR SINGLE-BORE If San José constructs its downtown subway using the single bore method, it will b the first in the world for a high-volume, heavy-rail transit sub- way. Demonstrating its viability here will position the nation as a leading innovator in transit, and will enable the construction of effective transit in many city centers where it would other- wise be impractical. BART's success as a high-capacity regional transit system has pushed ridership to its physical capacity limits. Inevitably, a sec- ond crossing of San Francisco Bay will have to be constructed. Given the relatively high development densities in San Fran- cisco and Oakland, the single-bore configuration in this crossing would provide significant benefits by expanding this successful system without the negative impacts of construction. Dennis Ratcliffe is an attorney and civil engineer serving as BART Extensions Program Director for the Santa Clara Valley Transporta- tion Authority.

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