Method of tunnel construction employing submerged caisson

A structure for underwater excavation comprising

• A. means defining a recess in the floor of a body of water, said recess having a ledge around at least a portion of its periphery;
• B. a completely submerged caisson shell received in said recess, the lower edge of said shell being disposed in vertical registration with said ledge;
• C. means in the shell defining a bell-type work chamber having
• (1) a bottom open to said recess floor, and
• (2) a closed top enabling it to contain breathable gas;
• and
• D. a sealing means between the lower edge of said work chamber and said ledge.

An excavation caisson comprising:

• A. a shell for placement at the floor of a body of water;
• B. means in the shell defining a bell-type work chamber having a bottom open to said floor;
• and
• C. means in the shell defining a passage to the interior of said work chamber, said passage-defining means including:
• (i) a conduit extending from the top of the shell to the top of the work chamber;
• (ii) a conduit extension extending from the top of the work chamber a part of the way to the bottom thereof;
• and
• (iii) closure means for said passage, said closure means including a first hatch at the top of the shell and a second hatch at the top of the work chamber.

An excavation caisson comprising:

• A. a shell formed from a vertical series of separable sections for placement at the floor of a body of water;
• B. means in the bottom section of the shell defining a bell-type work chamber having a bottom open to said floor;
• and
• C. means in the shell defining a passage extending through all of said sections to the interior of said work chamber.