86th Street Cavern

Sustainability and green

Skanska is the managing partner of the jointventure
awarded a $301 million project for
construction of the 86th Street Station cavern
portion of the new Second Avenue Subway. The
major facets of the project include mining of the
cavern via drill and blast methods, followed by
construction of the reinforced concrete structural
lining of the cavern. Additional work items
include building demolition, installation of
support-of-excavation elements, utility relocation
and reconstruction, and underpinning of
existing buildings adjacent to the work site. All
work will be performed in the densely populated
upper east side of Manhattan, making proper
maintenance and protection of pedestrian
and vehicular traffic through the area of paramount

The station cavern, approximately 1,100 feetlong,
seventy feet wide and sixty feet high, will
be excavated utilizing controlled drill and blast
techniques. Access to the work area will be
via two access shafts, started under a previous
contract and completed under this contract.
These shafts will also be utilized for the removal
of approximately 170,000 cubic yard of blasted
rock. The joint venture will utilize a specially
designed conveyor system to facilitate transfer
of the excavated material to disposal trucks at
street level. In conjunction with the excavation,
initial support of rock faces will be accomplished
by the use of rock-bolting and shotcrete
installation. Following excavation and initial
support of the cavern, a waterproof membrane
system will be installed prior to construction of
the final reinforced concrete structural lining. A
custom-designed form system will be utilized to
accelerate concrete wall and arch construction.

Other work on this project includes demolition
of several buildings in the area to permit
construction of the station entrances and utility
ancillaries. The demolition will encompass both
lead and asbestos abatement.

During demolition operations and construction
of the station entrances and utility ancillaries,
many of the adjacent building structures will
require temporary support of existing slabs,
walls and columns. The joint venture will design
and install temporary supports and ground
improvements to ensure the stability of both
building structures and utilities during these

Although much of the utility relocation is being
performed under a separate early-works contract,
the Joint Venture team will need to design
and install temporary utilities to facilitate installation
of station entrances and building support
elements. This work will require detailed
coordination with the numerous third-party
utility owners as well as the adjacent building

To mitigate the construction impact on local
residents, businesses, the traveling public and
emergency services, the joint venture will
undertake extensive temporary detour and
safety measures. These measures will include
temporary sidewalks; relocations of surface
features such as trees, benches, canopies and
stoops; variable message signs; protective
fencing and barriers. Throughout the duration
of the contract, the team will be required
to coordinate activities with numerous other
contractors working in the area and to provide
residents, community boards and local officials
with information about work progress and significant
activities impacting them.

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