Research Of The Method About Soft Base Of Saturated Loess Tunnel Processing

Soft base tunnel is a tunnel which is built on the soft foundation. Tunnel structure is an increasing proportion of the whole railway line of our country railway engineering construction in the mountain area currently, and loess soft base tunnel crops up frequently in railway engineering. Therefore, we urgently need further research the mechanism of lining support and estimate the foundation bearing capacity at arch feet of soft base tunnel as a special tunnel. So that we can decrease maximum diseases occurrence of soft base tunnel and establish the technique system of excavation process of soft base tunnel.This paper focuses on saturated and collapsed loess tunnel in china and bases on the project of baoji-lanzhou passenger dedicated railway line, we mainly make a study of following aspects:(1) A typical cross-section is selected to embed earth pressure cells, surface strain cells,reinforce bar stress gauge and concrete stress gauge in surrounding rock of tunnel, to grasp stress characteristics of surrounding rock and tunnel lining structure under long-term observation of surrounding rock pressure, stress in steel arch and stress between the first linings and the second linings, which evaluation the safety and stability of tunnel structures and the rationality of construction method.(2) Field test for the pile foundations of shangzhuang tunnel is instructed by calculating the bearing capacity, including test on the bearing capacity of single steel tube pile and steel tube pile composite foundation. The filed test can be further complemented by combining with the indoor model test of steel tube pile in different water content of loss, which also evaluating the treatment efficiency in piles foundation of soft base tunnel.(3) Based on field test of steel tube pile, this article simulates pile foundation treatment of this soft base tunnel by the finite element software MIDAS/GTS, and studies the effect of the bearing capacity of single pile foundation and group pile composite foundation in two different conditions.Finally, it summarizes the achievements and points out the insufficient of this essay, and raises the need for further research content.