Study On Construction Technology For Saturated Loess Section In Qinghai Dandong Tunnel Portal

At present, in order to adapt the needs of the development of national economy,the state increased investment in infrastructure construction,road and rail accounted for a large part among them. in these already built or under construction in highway and railway, contains some tunnels, and the construction of tunnel portals has been an emphasis and difficult point in tunnel engineering. especially in bad geological condition areas. compared to the other section of the tunnel, surrounding rock is generally weathered, and there are bad geological structures,such as joints, faults, fractured zones, and there is often a serious phenomenon of shallow buried bias. with the increasing of the large section tunnel, the research on key technology of the construction of the tunnel portal is more urgent.On the basis of summarizing the domestic and foreign research status about the tunnel portal construction in this article, combined with the specific problems of Dandong tunnel, such as the landslide of the portal excavated slope, upward slope couldn't support load, existing saturated soft loess at the bottom of the slope and under the cut open tunnel basis of 13 m to14m,the foundation bearing capacity can't meet the design requirements, the presence of buried gas pipeline at the left side of tunnel and natural gully which is substantially perpendicular with the tunnel axis at the portal right side of k38+070 location,to carry out the corresponding construction technology research. Research indicates that using steel pipe jet grouting pile strengthening the cutting slope excavation;cooperate with pile foundation and connecting beam strengthening ground of the cut open tunnel;using vertical rotary spray pile strengthening soft foundation and horizontal jet grouting pile strengthening soft loess can meet the requirements of design and construction;by extending the length of cut open tunnel with lead and drainage facilities to decrease the effects of natural gully remit of the remit of the tunnel, the effect is good through the actual inspection.Through field research and technology improvement measures and construction control, solving the existed engineering problems and hidden trouble of the Dandong tunnel portal, ensure the safety of the tunnel and the surrounding, providing a very good reference for the similar engineering problems in the future, it also provides a good engineering example.