Shallow Loess Large New Structural Stability Of Thetunnel Treatment Of The Base Collapsible

A large-scale construction of the tunnel construction in western China, large section of the loess tunnel would become the mainstream of future tunnel structure by effectively alleviating the high density of traffic flow. As a kind of special soil, the key of excavating tunnel is how to ensure the stability of surrounding rock and lining structure. Especially the tunnel in collapsible loess strata, how to reinforce the basement of the tunnel and eliminate the collapsibility of loess, ensure the tunnel basal bearing capacity satisfy the design requirements.This paper was based on Daying loess tunnel of Lanzhou Yu-ding road as the research object. Through general finite element software modeling and the engineering example of the heavy section loess of shallow buried tunnel, analysis of the loess tunnel structure and mechanical characteristics of surrounding rock during excavation of tunnel in loess tunnel and studied basement with no vibration of foundation compaction reinforcement application of new technology in this paper. the main research contents and research conclusions are as follows:(1) By simulating the excavation of the tunnel CRD construction method, we have analyzed the large section loess tunnel's strain and strain rate in the excavating process. It turned out that the initial supporting structures which have been applied on and the temporary supporting structures could be well controlled the distortion. After removal of the temporary supporting structures, the amount of the deformation and the deformation rate will appear increasing trend, so we should construct the lining in time.(2) The structural stability analysis of lining of Dayingcun tunnel has showed that the feet parts of the arch bridge both have appeared the phenomenon of large stress concentration under the seismic situation and the non-seismic situation, so we should reinforce the tunnel base to ensure the safety of the tunnel structure and meet the settlement requires after the construction.(3) By analyzing the test data of No vibration compaction reinforce technology, the reasonable pile spacing has been put forward when making loess foundation reinforcement. The tests showed that the wet sinking coefficient and the self-weight collapse coefficient of the earth between piles were both less than 0.015, when the distance between piles were less than 0.7m, and the eliminated the wet trapping, but it is not proportional relationship between the distance between piles and foundation compaction coefficient. When the distance between piles is 0.9m, the compaction coefficient on average and the minimum compaction coefficient could meet the requirements of which(GB50025—2004)have requested.Through the analysis of measurement data in engineering test, found no vibration of the loess confidential reinforcement technology in the foundation soil compacting process within the scope of the bottom 1 ~ 1.5 m, effective compaction pile diameter is less than the design(only 68.8% of the design of pile diameter), the average and minimum soil compaction coefficient between each pile in the pile bottom are less than the requirements(0.93, 0.88) that the collapsible loess areas building codes(GB50025-2004) specified.