Study on State and Pattern Analysis of Tunnel Portal Slope in Korea

Abstract

The number of tunnels are in fact increasing as a part of linear improvement project of general national highway and road enlargement and pavement project. Recently, collapses of portal slope are also occurring considerably, due to local raining from severe rain storm and abnormal weather. Accordingly, it was risen a necessity to efficiently respond to tunnel portal slope damage and maintenance in Korea and oversea nations. This paper is a basic proposal to execute a survey on the current status and state of the tunnel portal slopes that were already installed and are now being operated along general national highways, and also to execute state evaluation for the purpose of managing those effectively. As a research method, domestic tunnels were analyzed in accordance with geometrical shape such as access type, portal form, and tunnel type, etc. via field survey to analyze the types of tunnel portal slopes along national highways. State evaluation classification sheet is presented to divide classes for the danger state of the surveyed portal slopes, and then the related grades are divided. It is mainly aimed at classifying the tunnel portal slopes along national highways with using this state evaluation, to use it as basic data so that continuous maintenance can be executed in the future in accordance with danger classes. Table 1. Tunnel dispersion status along the national highways in Korea. Regional Offices Total Seoul Wonju Daejon Igsan Busan No. of 105 28 20 23 20 24 tunnel Average 608 458 653 729 607 568 length due to the topographical causes such as access type, etc. mentioned earlier. To see it by regional office, the number of portals of Seoul Regional Office are 23, which shows the least dispersion, and the numbers of portals of Wonju Regional Office, Iksan Regional Office, and Busan Regional Office are similar each other. For the analysis on tunnel portal slope, the respect tunnel field was divided into entrance and exit. Also, to analyze the portal in detail, it was divided into the location of portal, single tunnel, and double lane tunnel. The reason why is that can be used in maintenance system in the future, which will be applied in view of maintenance. Table 3 shows the result of analysis on the number of tunnels per tunnel type and tunnel extension. From Table 3, “single lane parallel tunnel” refers to a couple of tunnels of which portal’s locations are the same and up/down streams are divided into two tunnels, while “double lane tunnel” refers to a tunnel of which up/down streams are the same. Also, “single lane tunnel” refers to a tunnel that just one lane among up and down streams is made by tunnel. As a result of analysis, it shows that single lane parallel tunnels occupy most of tunnels in Korea. In case of single lane tunnel, there is Maamsan tunnel in the jurisdiction of Jinyeong office, of which down stream lane is made by tunnel, hence it is only one tunnel of the case. For tunnel length, it was surveyed that Chuwolsan tunnel in the jurisdiction of Gwangju office is the shortest while the longest one is Bakdaljae tunnel within the jurisdiction of Chungju office. The location and types of tunnel portals were analyzed in view of maintenance such as future maintenance and introduction of real-time monitoring system. Table 4 is the results of analysis on access types and portal form. First, analysis on access types will be presented and then the analysis on portal form will be described. Generally, the access type of entrance of tunnel is influenced the most from topography or weather, which may be divided into total of 5 types depending on the relation between topography and tunnel central axis: “slope orthogonal type”, the best idealistic location 118 Table 2. The numbers of tunnels and portal slopes per management offices. Regional construction Highway maintenance & Number of Number of Number of management offices construction offices tunnel name portals tunnel sites Seoul Suwon 2 6 4 Uijeongbu 7 17 14 Wonju Hongcheon 12 26 16 Gangneung – – – Jeongseon 4 8 4 Daejon Nonsan 5 10 7 Chungju 7 17 14 Boeun – – – Yesan 1 1 2 Igsan Gwangju 6 15 9 Jeonju 1 2 1 Namwon 4 8 5 Suncheon 3 8 5 Busan Daegu – – – Jinju 2 4 4 Pohang 4 8 6 Yeongju 7 14 10 Jinyeong 3 6 4