Tunnel undercrossing construction process

The embodiment of the invention discloses a tunnel undercrossing construction process, and relates to the technical field of tunnel construction. The tunnel undercrossing construction process comprises the steps of S1, performing advanced support, wherein a pipe shed is combined with an advanced small guide pipe to form the advanced support, and adjacent end parts of pipe sheds of two adjacent segments of advanced support are coincided in a radial direction of the tunnel to achieve mutual overlap joint; S2, performing advanced curtain grouting, grounding a surrounding part of the advanced support in the step S1 in advance before tunnel face excavation, and reinforcing a surrounding rock; S3, performing tunnel excavation; S4, performing tunnel support and water-proof and drainage construction; and S5, performing lining construction. Dual layers of advanced pipe sheds are combined with the advanced small guide pipe to form the advanced support, the advanced support is combined with all-fracture advanced curtain