Connecting channel construction method of existing underground structure in weak water-rich stratum

The invention discloses a connecting channel construction method of an existing underground structure in a weak water-rich stratum. The method comprises the following steps of 1, constructing a waterproof curtain; 2, reinforcing bottom soft soil; 3, reinforcing upper soft soil; 4, reinforcing soft soil at an excavating region; 5, secondarily reinforcing the upper soft soil; 6, separating an external wall and building envelope; 7, disassembling the external wall and building envelope; 8, excavating one half of soil body and performing preliminary supporting; 9, excavating the other half of thesoil body and performing preliminary supporting; 10, constructing a connecting channel structure; 11, performing supporting and disassembling; 12, executing the steps 8-11 repeatedly till excavation and structural construction of the whole connecting channel are completed; 13, disassembling the external wall and building envelope of the underground structure at the other end of the connecting channel. Accordingly, constru