THE RESEARCH OF ENGINEERING GEOLOGICAL ROUTE SELECTION IN XIAOJIANG FAULT ZONE OF DONGGE EXPRESSWAY

Due to the limitation of topography, economy and planning conditions, Dongge Expressway must be spread in Xiaojiang fault zone. It is the first expressway with all lines located in Xiaojiang fault zone. Xiaojiang fault is a regional Holocene active fault with complex geological conditions along it. The engineering geological characteristics of Xiaojiang fault zone and its different effects on cutting, bridges and tunnels are the primary controlling factors for engineering geological route selection of Dongge Expressway. On the basis of collecting the existing research results of Xiaojiang fault and adopting comprehensive means such as detailed engineering geological mapping, drilling, geophysical prospecting and remote sensing, the engineering geological conditions of several alternative schemes along the Xiaojiang fault zone are accurately analyzed and evaluated, and the junction position of the eastern and Western branches of Xiaojiang fault is preliminarily determined, thus the reasonable route scheme is determined. Several principles for route selection of Expressway Engineering in mountainous areas within Holocene active fault zone are summarized as follows:the main laying methods of the project should be subgrade, short tunnel and low bridge, and the engineering types which are difficult to repair when earthquake damage occurs, such as long tunnel and high bridge, should be used as little as possible; the tunnel engineering should avoid the central position of fault fracture zone or surface fracture zone as far as possible, cross fault fracture zone as short distance as possible, and avoid multiple fault junction positions as possible. Tunnels should be set up and the strike of the line should avoid the mixed accumulation platform or terrace with complex origin in the fault zone as far as possible.