Study On Construction Technique Of Traffic Tunnel Portal Of Houziyan Hydropower Station

Tunnel portal is the throat of a tunnel, its construction quality directly affects the quality and progress of the whole tunnel engineering. The surrounding rock of tunnel portal is generally broken, weathered seriously and the cover layer is thin, So the stability of surrounding rock is poor. During construction, the principle of "early entering and late exiting" is usually followed in order to reduce the disturbance to the surrounding rock and enhance the stability of the slope. Therefore, it is very important to select the reasonable construction method for tunnel portal.In order to select the reasonable and feasible construction method for the traffic tunnel portal of Houziyan Hydropower station. This paper has summarized the main construction methods of the tunnel portal and compared of the applicability of the methods at home and abroad through consulting a lot of data. The main supporting measures and the mechanism of the tunnel portal have been introduced. It also has introduced the main support measures of tunnel portal and its action mechanism. According to practical situation of traffic tunnel portal of Houziyan Hydropower station, this paper has used numerical calculation method to simulate the construction process of the tunnel portal with bench method, CD method, and CRD method and has compared and anlysised the feature of displacement and stress and plastic zone distribution of surrounding rock and the internal force of support structure.Considering the construction cost of the three construction methods, Recommend to choose CD method as the construction method of traffic tunnel portal of Houziyan Hydropower.For CD method, a detailed excavation and support scheme and monitoring measurement scheme are established according to practical situation of traffic tunnel portal of Houziyan Hydropower station. By analyzing the measured data, applying the CD method into the traffic tunnel portal of Houziyan Hydropower station is safe and feasible.The conclusions of this paper provide theoretical support on the construction of traffic tunnel portal of Houziyan Hydropower station. At the same time, the successful application of CD method at construction site further proves the conclusion of numerical calculation. In this paper, it has been studied on the mechanical properties of tunnel which is in the soft broken rock, and the results can provide reference for similar projects in the future.