Control method for keeping stable excavation face in earth pressure shield driving in upper-soft lower-hard ground

The invention relates to a control method for keeping a stable excavation face in earth pressure shield driving in upper-soft lower-hard ground. A slurry pipe is installed in a cutterhead abdominal cavity, and a sprinkler is connected. In a cutting process of a cutterhead, slurry is sprayed to the excavation face, and the slurry is permeated to the excavation face under the action of compressed air, so a soil film is rapidly formed on the excavation face, and a support pressure is effectively built on the excavation face. At the same time, the slurry or high-molecular polymer solution is poured into a pressure cabin, and residue soil is stirred until the residue soil is in a plastic flow state. The method has the following advantages: 1) the slurry forms the soil film on the excavation face under the action of the compressed air, the compressed air can be prevented from escaping, the support pressure is effectively built on the excavation face, and the excavation face is kept stable; 2) the extrusion action o