The design and construction of separate tunnels, small netspacing tunnels and doublearch tunnels should follow the principle of trying to maintain the initial state of the surrounding rock mass and the minimum energy principle. If the tunnel structure is rationally designed and the tunnel construction is scientifically organized, the structural forcebearing independence of small netspacing tunnels and doublearch tunnels can be almost maintained. The lining pressures and internal forces of the optimized crosssections of doublearch tunnels are distributed almost symmetrically and are comparable to those of separate tunnels. Doublearch tunnels with optimized crosssections are a reasonable type of doublearch tunnels.