The Parallel Thimble Shoal Tunnel Project will construct a new two-lane tunnel under Thimble Shoal Channel. When complete, the new tunnel will carry two lanes of traffic southbound and the existing tunnel will carry two lanes of traffic northbound. Cascade’s role in this project was to help collect critical subsurface geotechnical information, along with core samples, that will be used in a pre-dredge elutriate study.
Our client needed the ability to obtain high quality core samples within highly saturated unconsolidated material too deep and difficult for “vibracore.” They also needed the flexibility to conduct traditional geotechnical sampling on the same drill platform. Also, since this work was being conducted in the main channel, it was important to have a drilling technology that would be the most efficient, productive, and pose the least risk of tooling loss.
Cascade successfully satisfied our client on all of the requirements of this project though an approach which utilized our over water sonic drilling technology, Lexan Liner Core system and standard SPT sampling tools. With these, Cascade was able to deliver to the client a near 100% continuously recovered core sample in 5-foot Lexan liners through using the Sonic drill core system in this material, while at the same time collect valuable geotechnical information. The client was then able to use the core samples for elutriate testing in their lab to help determine a dredge material disposal budget. In addition, Cascade provided conventional geotechnical samples to help fill-in data gaps for the Base Line Geotechnical Report.