Manhattan Approach Tunnels (CM009) Tunnel boring machine (TBM) equipment has been delivered and a TBM assembly chamber has been constructed.

Following construction of the TBM in the assembly chamber, tunnels will be bored via four TBM drives from the existing tunnel under 63rd Street and Second Avenue to the south end of the GCT tail tracks.

Queens Open-Cut Excavation (CQ028)
An open-cut structure is being created and then decked over to serve as the TBM launch area for the Queens tunnels prior to its permanent use as an interlocking and an emergency exit/ventilation facility. The shaft that was completed in November 2003 is being expanded via tunneling under Northern Boulevard (requiring underpinning of the Brooklyn-Manhattan Transit “BMT” structure) into LIRR's existing rail yard.

From the Lab
Interface Shear Test

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The upper box usually contains the soil or another geosynthetic. A normal load is applied to the top then the upper box is moved horizontally across the lower box. During the test, the horizontal force required to move the top box and the horizontal displacement are measured and recorded. This is usually repeated at least two additional times with different normal loads. The results are graphically reported in a plot of shear force vs. corresponding normal load to determine a strength envelope (friction angle and cohesion).

Several parameters which affect interface shear test results should be determined by the design engineer and conveyed to the laboratory prior to testing. These parameters should be chosen with the site conditions in mind so as to replicate in-situ conditions as closely as possible. These parameters include:

• Normal loads and consolidation time – Specifying the appropriate normal loads ensures that the test is conducted at conditions which will exist in the field. Consolidation time will depend upon what is expected to happen in the field. This will greatly affect pore pressure in the soil and will have a major impact on the measured shear resistance.

• Hydration times and seating loads for GCLs – This is important because the strength properties of GCLs change dramatically once given access to water and allowed to either swell or consolidate. Therefore, the load applied during hydration can also have a great affect on the GCL’s strength.
  
  
• Soil density and moisture content – Compacting the intended soils to the same density and moisture content that will be required in the field ensures that an artificially high or low shear resistance isn’t measured.
  
  
• Shear rate – It is critical to specify the correct shear rate because running a test too quickly can generate pore
  pressures on the failure plane which may not be representative of field conditions and will most certainly yield incorrect shear resistance values.