Underground water treatment method for underground excavation construction in compound stratum below existing building

The invention discloses an underground water treatment method for underground excavation construction in a compound stratum below an existing building. The underground water treatment method comprisesthe steps that (a) open cutting of a hall body structure is completed; (b) four sectional drainage pipes are uniformly driven into four quadrants of a CRD in an underground diaphragm wall, and one auxiliary sectional drainage pipe is arranged at the center; (c) the underground diaphragm wall is sequentially chiseled away part by part; (d) a primary support, a temporary vertical support and a temporary horizontal support of the underground diaphragm wall within the thickness range are constructed, and C25 early strength concrete is ejected in the erection process; (e) right and left lines aredrawn to conduct underground excavation of a large pipe shed of an arched part of a main tunnel, and water sacs on a soil-sock combination surface of the arch part are actively released; (f) groutingis conducted on the advance