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    Continued Construction Work For The WTC Transportation Hub

December 28, 2005

The following comprises additional preliminary design plans at the 35% design completion level for World Trade Center (WTC) Site construction work related to the WTC Transportation Hub project, which may impact certain WTC Site Historic Resources. The design plans below reflect the review and comment by the Project Historic Architect (PHA), as stipulated by the Resource Protection Plan (RPP) (Section 2.2 Design Phase Responsibilities).

The scope of work depicted in these plans is comprised of:

* Temporary underpinning of the New York City Transit (NYCT) 1 Line Subway Box - to provide for expanded connections between the western and eastern portions of the WTC Site for the WTC Transportation Hub Project as well as create additional space within the WTC Site for various stakeholders to utilize for their programs. The NYCT 1 Line Subway box structure will be temporarily underpinned. This would enable subway operations to continue across the WTC Site while permanent structures to accommodate various program needs are constructed in the future. (See Figure 1 and Figure 2)

* East Bathtub Excavation and Construction – This project will provide for new subgrade areas on the eastern portion of the WTC Site to accommodate the future Transit Hall and extent of North-South pedestrian connections

o East Bathtub Construction – This work will consist of the installation of a new slurry wall along Vesey Street between West Broadway and Church Street, Church Street between Vesey Street and Fulton Street, Church Street between Cortlandt Street/Way and Liberty Street, and along Liberty Street from Church Street to Greenwich Street. The new slurry wall will be designed to connect to a significant portion of the existing Hudson and Manhattan (H&M) Railroad basement wall along Church Street to create the full bathtub walls for the eastern portion of the WTC Site. (See Figure 1 and Figure 3)

o East Bathtub Excavation - Once the new slurry walls are installed, the interior of the eastern portion of the site will be excavated down to bedrock to create the bathtub structure in preparation for the future construction of the WTC Transportation Hub.

As a result of the Underpinning and East Bathtub Excavation and Construction Work, the Port Authority of New York & New Jersey (Port Authority) has determined that the following areas of the WTC Site Historic Resource will be impacted:

# 1 Line Underpinning – Effect on Existing 1 Line Subway Box Structure :

* The underpinning project will consist of installing minipiles and structural steel framing within and around the subway box in order to create a support structure for the subway box. In order to install the minipiles located between the tracks and through the platform areas, cores will be installed into the subway box roof and invert. Drill rigs will then be positioned on the subway roof to auger a passageway for the minipiles to be installed to the rock subsurface. Structural framing will then be installed to connect to the minipiles and existing subway box framing, allowing the subway box to eventually be supported by the framing. (See Figure 2)

During the construction, work will take place near the existing west bathtub east slurry wall. As stated, minipiles will be installed (augered into place) immediately adjacent to the subway box between the subway box and existing wall. After the minipile installation, the Contractor will locally excavate adjacent to the subway box to expose the subway box structural framing for connection to the augured minipile. (See Figure 2)

# 1 Line Underpinning – Additional Excavation and Effect on West Bathtub East Slurry Wall :

* Once all of the structural steel supports are in place and the existing subway box is connected to it, the soil located beneath the subway box will be excavated. Upon excavation, the subway box will be supported by the minipile and steel installation, creating space below the box for site program. The FEIS discusses tunneling through the east slurry wall at three locations, which could occur simultaneously, representing a snapshot in time of the construction activities during the peak period of construction. As engineering designs were advanced, tunneling from the west bathtub was no longer necessary as excavation of the east bathtub would allow for the 1 Line to be underpinned from the east side. However, since the existing east slurry wall of the west bathtub was designed to resist the soil pressures created by the soil below the subway box, upon excavation serious concerns have been raised about the east slurry wall’s structural stability. Given the resultant condition and associated safety concerns, a large part of the upper portion of the slurry wall is planned to be removed from elevation 264’ and above; leaving the slurry wall intact from bedrock to elevation 264’, alongside the track and platform area. (See Figure 2)

# East Bathtub Excavation and Construction Work :

* Remnants of the former H&M Structure – Portions of the former H&M Structure remnants at the WTC Site will be demolished to permit the construction of future site program. This includes the ring sections below the 1 Line Subway box as well as in the areas of excavation of the East Bathtub. During excavation, a few ring sections will be extracted and if found to be in salvageable condition, transported to Hangar 17, John F. Kennedy International Airport (Hanger 17). In addition, 2 ring sections will be removed and used for evaluation and testing as part of the PATH Tunnel Security Program. The portion of the H&M bathtub wall along Church Street will remain and become a part of the future east bathtub wall and future WTC development. In order to stabilize the existing wall in its current location and absent of its support slabs, tiebacks will be installed to provide lateral restraint for the wall against the existing soil pressure due to Church Street. (See Figure 3)

* Steel in the form of a cross – The steel in a form of a cross structure is currently mounted to the existing H&M structure. The project will demolish a majority of the remaining components of the former H&M Structure remnant, including the portion of the structure supporting the steel in the form of a cross. As a result, the steel in the form of a cross structure will be removed from its support and transported to Hanger 17 (or an alternate location to be determined) until its final location is determined. The temporary relocation and transport of this artifact will conform to the RPP. (See Figure 1 and Figure 3 and Photo 1)

* Remnant of the former Vesey Street Access Stairs – As referenced in the FEIS and ROD, the WTC Transportation Hub project will involve excavation of the east bathtub. A portion of the scope of the east bathtub construction will be to excavate the site below the Vesey Street Access Stairs remnant to the depth required to allow for the WTC Transportation Hub project to be constructed. (See Figure 1 and Figure 3). The east bathtub construction scope shall therefore include maintaining the remnant in its current location by underpinning the structure and bracing the supports during excavation. The condition and appearance of the structure at grade will not be affected by this work. (See Figure 1 and Figure 3 and Photo 2 and Photo 3). The final disposition of the Vesey Street Stairs is not within the scope of the WTC Transportation Hub project as discussed in previous Section 106 Consulting Parties meetings and as referenced in the ROD.


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