On October 8, 2013, the Chesapeake Bay Bridge-Tunnel Commission awarded Jacobs the supplemental agreement to perform the geotechnical investigation in the amount of $4,785,200.
The work included conducting a thorough geophysical and geotechnical investigation for expanded Islands 1 and 2, approach trestle foundations, and the proposed immersed tube tunnel alignment. Work done under this agreement included 20 test borings and 38 Cone Penetration Test (CPT) probes. Due to the deep water along the channel, Fugro Atlantic, as a subconsultant to Jacobs, mobilized a jack-up vessel from the Gulf Coast. The borings were drilled to depths of 80 feet to 200 feet below mean low water level. The CPTs were pushed using a Roson or Seacalf Seabed system. The CPT seabed system can be used with cones, T-bars and In-Situ Vanes.
The geophysical investigation employed a Seismic Reflection System, high resolution Compressed High Intensity Radar Pulse (Chirp) system and a R2Sonic or Reson 7125 multi-beam echo sounders to complete the geotechnical investigation. Chirp systems employ wideband frequency modulated (FM) “Chirp” technology. The sub-bottom Chirp system provides the data to image the near-seafloor sediments. Side scan sonar technology was used to map the extent of the armor and riprap stone around the existing islands, and debris along the tunnel and island footprints. In addition, a full multi-beam bathymetric survey was performed on the project site.
This work was completed the summer of 2014.