Mechanical tunneling construction method for large-span multi-arch hard rock tunnel

The invention discloses a mechanical tunneling construction method for a large-span multi-arch hard rock tunnel. The mechanical tunneling construction method comprises the following steps that firstly, planning is conducted before construction; 2, constructing a middle pilot tunnel; step 3, constructing an upper step; 4, lower step construction; 5, inverted arch construction; wherein in the first step, the whole section of the large-span multi-arch tunnel is divided into seven parts including a middle pilot tunnel, a left tunnel upper step, a left tunnel lower step, a left tunnel inverted arch, a right tunnel upper step, a right tunnel lower step and a right tunnel inverted arch, and the middle pilot tunnel, the left tunnel upper step and the right tunnel upper step are excavated through a cantilever heading machine; the left hole lower step, the left hole inverted arch, the right hole lower step and the right hole inverted arch are excavated through hydraulic breaking hammers; a tunneling mode of synchronous