Structure and method for constructing tunnel portal of connecting channel through mechanical method

The construction structure comprises a main line tunnel pipe and a heading machine trolley, the heading machine trolley is located in the main line tunnel pipe, a connecting channel tunnel portal is horizontally formed in one side of the main line tunnel pipe, and a propelling structure is fixedly connected to the heading machine trolley; a construction part is fixedly connected to the side, close to the connecting channel portal, of the propelling structure and comprises a force application cylinder fixedly connected to the propelling structure. The tunnel portal sleeve is used for supporting the connecting channel tunnel portal, so that the tunnel portal sleeve becomes a part of a tunnel portal structure, the influence of tunnel portal coring on the structural strength of main line tunnel segments is reduced, the strength is guaranteed, and therefore the traditional mode that glass fiber rib special lining composite segments are arranged in a main line tunnel is not needed; the problems that main line speci