Construction method suitable for up-down overlapped tunnel with small clear space and long distance under weak geological condition

The invention discloses a construction method suitable for an up-down overlapped tunnel with the small clear space and long distance under the weak geological condition. The up-down overlapped tunnel comprises an upper hole tunnel body and a lower hole tunnel body, wherein the tunnel diameter of the upper hole tunnel body is the same as that of the lower hole tunnel body, and the tunnel length of the upper hole tunnel body is largely equal to that of the lower hole tunnel body. Both the upper hole tunnel body and the lower hole tunnel body are of a tunnel structure formed by tube pieces, the vertical clear space between the upper hole tunnel body and the lower hole tunnel body is smaller than 0.7D(shield diameter), and the tunnel length is larger than 1000 m. The shield construction method includes the steps that after the lower hole tunnel body is completed according to a conventional shield construction method, the measures of a shield high-altitude starting platform, up-down tunnel interlayer soil body deep hole grouting reinforcement, lower hole tunnel supporting steel ring reinforcement, a shield high-altitude receiving platform and the like are taken, so that the influence on the formed lower hole tunnel body by shield construction of the upper hole tunnel body and the secondary overlapping effect of overlapped tunnel sedimentation are reduced, and it is guaranteed that deformation of the lower hole tunnel body and ground subsidence can be controlled. The overlapped tunnel shield construction method is of great reference value and practical significance to similar shield tunnel engineering and intensive deep-layer underground space exploitation and utilization.