Research Of Excavation Technology Of Tunnel With Loess-Rock Interface Geological Condition

With the development of transportation infrastructure in the western area, engineering encountered an increasing number of loess covered tunnel.During the construction of tunnel excavation, we will inevitably face the special geological problem when excavating through the loess-rock interface.it is very useful for theory and engineering to research the tunnel excavation technology,in this special condition.This theses establishes three-dimensional model used by Finite Different software Flac 3D and carries on numerical analysis. The topic of the theses is the technology of tunnel excavating, under the special geological condition of loess-rock interface. one is simulating under the up-down step excavating condition, analyzing the features of failure behavior of the loess-rock interface tunnel-surrounding rocks, then making prediction the landslide area and size of the tunnel-surrounding rocks near the loess-rock interface; based on the prediction above on,the other aspect puts forward three treatment measures,and prove the feasibility of them.It mainly analyzes and proves effective from three aspects:Loess-rock interface of changes in shear displacement; Loess-rock interface near the side-slip displacement changes in soil; the plastic zone near the soil side of Soil-rock interface and internal force change in initial supporting.The following understanding is made:1) In the up-down step excavating, when the tunnel face nears the soil-rock interface, Loess-rock interface takes place a great deal of shear displacement, which maximum value is 0.4975 meters;so that the surrounding rock of Loess-rock interface near the soil side appeared a large-scale plastic zones. In the loess-rock interface, Early Support's tensile stress was too large and damaged. With the destruction of the initial supporting structure, the landslide areas appeared in tunnel roof was roughly shaped a half upside-down teapot.2) For the engineering problem of landslide occuring in the 120°surrounding rock area near the loess-rock interface, proposing to take three methods to excavate--Excavation using the ring cutting method, Excavation of CD Method, Excavation of CRD method under using grouted small pipe advanced support in landside areas. They all can effectively control the loess-rock interface may occuring landslides over the tunnel roof. 3)Comparing the three enhanced supporting and excavating methods, CRD method is the best one in controling the relative slip of the tunnel roof surrounding rock, his method divided the whole cross section into six small working area,using one vertical interim support and two Lateral support. CD method is the better one dividing the whole cross section into two ones, using one vertical interim support. The ring cutting method is the latest choose. However, considering the economic efficiency, the ring cutting method is the best economic,next is CD method,finally is CRD method.