Existing subway tunnel protection structure adjacent to excavated foundation pit and construction method

The invention provides a protection structure of an existing subway tunnel adjacent to an excavated foundation pit. The protection structure comprises two rows of meat and vegetable secant piles, secant pile crown beams, a soil body transverse reinforcing area, parallel connecting beams and stress unloading holes. The two rows of meat and vegetable secant piles are arranged on the two sides of the existing subway tunnel respectively. The secant pile crown beam is arranged at the top of the meat and vegetable secant pile; the soil body transverse reinforcing area is arranged at the bottom of the meat and vegetable secant pile and used for transverse reinforcing; the parallel connecting beams are arranged between the tops of the meat and vegetable secant piles; the stress unloading holes are vertically formed in the sides, away from the excavated foundation pit, of the meat and vegetable secant piles. The invention further provides a construction method of the protection structure. The device has the advantages