I recently had the opportunity to train a crew on a very interesting job inside an underwater utility tunnel beneath a lock and dam in the St. Lawrence Seaway. This seaway connects the Great Lakes to the Atlantic Ocean. This tunnel is underneath a giant concrete deck, so the walls have taken a lot of pressure over time. The soil also shifts and settles underneath the tunnel as the years go by. Those factors, in addition to freeze/thaw cycles have caused cracks to appear in the walls.
One particularly large crack was 20 feet long and up to 2 inches wide in some places. The water leaking through created an especially dangerous situation considering the 480 volt electrical box you can see in the photo above. There is also plenty of valuable equipment in the tunnel that is susceptible to water damage.
I suggested to the customer that they buy about four 5 gallon pails of Spetec F400. I recommended this material because it works very well in wet joints and cracks. It also remains somewhat flexible after installation, so if the walls settle or shift a little more, the cured grout will not break. When I showed up we got to work immediately with our on-the-job training, using modified airless sprayers to pump the material. Overall, it took about 2.5 hours for the crew to get the job done while learning the leak seal process at the same time.