Advance support structure for tunnel with huge variable cross section

The utility model provides an advance support structure for a tunnel with a huge variable cross section. The structure comprises a tunnel cross section which is formed by a to-be-excavated main tunnel and to-be-excavated side tunnels, the to-be-excavated side tunnels are located on two sides of the to-be-excavated main tunnel, two layers of high pressure horizontal chemical churning piles are arranged on the arch of the to-be-excavated main tunnel along the outside of the tunnel excavation contour line, advance long steel pipes are embedded between the two layers of chemical churning piles, a layers of high pressure horizontal chemical churning piles is arranged on the arch of each to-be-excavated side tunnel along the outside of the tunnel excavation contour line, a plurality of high pressure horizontal chemical churning piles are arranged on the arc feet between the to-be-excavated main tunnel and the to-be-excavated side tunnels along the outside of the tunnel excavation contour line, and a plurality of high pressure horizontal chemical churning piles are arranged on the tunnel face arch of the to-be-excavated main tunnel along the outside of the tunnel excavation contour line. According to the advance support structure for the tunnel with the huge variable cross section, the safety for excavating the tunnel with the huge variable cross section in particularly soft surrounding rock is ensured, the use of a temporary support is reduced, the operation freedom degree is increased, and the construction speed is accelerated.