Excavation construction method for subsurface tunnel in discontinuous lithologic stratum

The invention provides an excavation construction method for a subsurface tunnel in discontinuous lithologic stratums, which comprises the following steps: step 1, when lithologic grades of upper and lower stratums of the same section are different during construction, completing advance support, and excavating a first preset area determined according to a lining type boundary; 2, reinforcing the reinforcing areas close to the arch feet on the two sides, and performing first-type primary support on the A-type surrounding rock; 3, a second preset area below the lining type boundary is excavated, and second-type primary support is conducted on the B-type surrounding rock; and 4, after waterproof plate laying is conducted on the tunnel, secondary lining construction is conducted at a time. According to the method, surrounding rock disturbance can be reduced in the construction process, the overexcavation amount is reduced, and the collapse accident rate under the unfavorable geological condition is reduced. 本申请提