Helix Line Development Application Of Research In Mountain Highway

Helix line development is a method for change the routes high degree of increase or decrease, the routes overcome the elevation difference to extend the distance to the same turning (clockwise or counterclockwise), and the upper and lower cross the road before and after, the intersection of routes interchange by the tunnel or Overpass Bridge. It spiral using of hill ridges by dry bridge or tunnel across lines; also in the valley, local circuitous route, the construction of a bridge across line. It is high cost because of tunnels or high bridge, Long Bridge; low grade highway is less used. As the development of social and economic, highway extend to the mountain depth. When using natural development unable to overcome the elevation difference between the control points, Helix line development begin to receive attention because it has better line conditions than back development and the potential of meet mountain highway alignment. At the same time, with the continuous enhancement of bridge and tunnel construction, Helix line development will play a unique value in Mountain Highway. But the application of helix line development in mountain highway is still in the exploratory stage, in the mountain highway route selection, it need for in-depth study in the use of Helix line development and its technical indicators to protect traffic safety.With the highway construction experience gradual accumulation, people'understanding gradually go deep into "safety, environmental protection, comfort, harmony". This paper defines the concept of Helix line development, concludes its features and favorable terrain, compares it with the natural and back development, demonstrate its feasibility in mountains highway from the technical, safety, economic and environmental.According to the highway helix line development characteristics that horizontal alignment is a continuous curve of the small radius and vertical section is mainly of the larger one-way slope, this paper works out the design indicators considering the night stopping sight distance out of the tunnel, the minimum radius considering the stopping sight distance and cross slope in the tunnel, the largest longitudinal slope and the slope length in consecutive downhill path, the design indicators of vertical section in one-way uphill section. These indicators have guiding significance in the helix line development. On the basis of determining highway helix line development indicators, this paper study its design principles, steps and method of linear, study the separate roadbed in design line location of horizontal curve, design line location of vertical curve, cross slope of standard cross-section, the location of superelevation rotational axis, the mode of superelevation transition, the horizontal and vertical design of the point in divided and incorporate roadway, the separation of roadbed collectivity design, the transition method of cross-sectional in the tunnel entrance.Researches the results of line safety evaluation at home and abroad, refined the evaluation methods in the "Guidelines for Safety Audit of Highway", complement its insufficiency. Analyses the line characteristics of helix line development, define the evaluation vehicle, put forward the evaluation criteria based on the "speed difference," "vehicle speed difference" and "velocity gradient", put forward the correction mode to consider changes in cross-sectional, long Bending Slope section and tunnel section. Theses results can be applied in the helix line development to ensure that the line design continuity and consistency.From the stage of design, construction and operation, the security measures of helix line development was put forward. At the design stage, operating speed is used to evaluate the line safety, to modify the horizontal and vertical route design indicators, cross slope and sight distance; to reduce traffic accidents by vocal shoulder belt, road alignment inducement mark, the strengthening guard rail out of the lateral curve, and other measures; take full advantage of the terrain, emergency escape lane and large vehicles cooling stations should be set up. During the construction phase, new technologies and new materials should be actively used to improved road friction coefficient. During the operational phase, we must strengthen safety management, and constantly improve the safety facilities, strengthen the management for overloading and over speeding, and enhance driver safety education.