Abstract:

The key technical points of design and construction of extremely largespan loess tunnel, i.e. high slope protection of tunnel portal, rapid tunneling, crossing underneath existing buildings and structures, tunnel deformation control, sinkhole backfill treatment of ground surface and ground surface fissures treatment measures, are discussed by taking engineering projects as examples. Some conclusions are drawn as follows: 1) The tunnel portal excavation scheme should be selected according to the actual conditions; the high slope scheme can be adopted if it was of great risk by early tunnel portal excavation scheme. 2) Large tunneling footage should not be suggested when threebench sevenstep excavation method is adopted; the construction organization optimization, working procedure connection strengthening, short footage and rapid cycling are the keys. 3) The settlement of loess tunnel can be effectively controlled by adopting partial excavation method, strengthening advance support, decreasing excavation footage and closing inverted arch timely. 4) As for the sinkhole，the backfilling measure by using limesoil with ratio of 3〖DK〗∶7 and liquid cement is reliable. 5) The ground surface fissures are apt to occur in shallowburied section and can be control by tunnel supporting; as for the existing fissures, effective measures should be taken in time.

Key words: extremely largespan loess tunnel, design and construction, tunnel portal protection, rapid tunneling, backfill treatment, settlement control