Research Conclusions: The construction program of adopting double-under-wall pilot tunnel is suitable for treatment of the foundation of shallow and extra large span tunnel which requires strict control of decline volume of surface under bad condition of building wall rock. It is easy to operate and control deformation because of the small section of double- under-wall pilot tunnel, and the stressed condition is improved much because of adopting the support with full section enclosure. In addition , the geological condition can be surveyed clearly and the foundation can be treated in advance for providing enough bearing capacity of foundation for supporting tunnel because of the construction of pilot tunnel in advance. The steel pipe pile for treating foundation can enhance the bearing capacity of the soils between the piles, improve the inverted arch foundation of the tunnel and form large inverted arch foundation against the settlement of entire tunnel.