Portal Slope Research Articles

Slope stability analysis and landslide hazard assessment in tunnel portal area

본 연구에서는 터널 갱구사면을 대상으로 사면안정성 및 산사태 위험도를 평가하였다. 먼저 사면안정성 해석을 통해 붕괴위험도가 가장 높은 구간을 선정하고 구체적인 붕괴규모를 파악하였다. 해석결과 해발고도 485~495 m인 구간은 강우시 안전율이 0.99로 불안정한 상태로 나타났다. 이 때 붕괴심도는 최대 2.1 m이며 붕괴 길이는 사면의 경사방향으로 18.6 m로 분석되었다. 해당구간에서 사면붕괴 시 파생되는 사태물질의 이동특성을 실시간으로 분석하고 터널 갱구부에 미치는 영향을 파악하고자 산사태 시뮬레이션 해석을 수행하였다. 해석결과 사태물질은 7.74 m/sec의 평균속도를 보이며 주로 계곡부를 따라 산 하부로 이동하는 것으로 분석되었다. 사태물질은 산 하부로 갈수록 점차 확산되며 10초 후에 터널 갱구부 위를 지나고 20.2초 후에 산하부에 도달하는 것으로 분석되었다. 특히 터널 갱구부는 사태물질 이동경로의 중심부에 위치하고 있어 산사태 발생 시 직접적인 피해를 받는 것으로 나타났다. In this study, the slope stability analysis and the landslide hazard assessment in tunnel portal slope were carried out. First, we selected highly vulnerable areas to slope failure using the slope stability analysis and analyzed the slope failure scale. According to analyses results, high vulnerable area to slope failure is located at 485~495 m above sea level. The slope is stable in a dry condition, while it becomes unstable in rainfall condition. The analysis results of slope failure scale show that the depth of slope failure is maximum 2.1 m and the length of slope failure is 18.6 m toward the dip direction of slope. Second, we developed a 3-D simulation program to analyze characteristics of runout behavior of debris flow. The developed program was applied to highly vulnerable areas to slope failure. The result of 3-D simulation shows that debris flow moves toward the central part of the valley with the movement direction of landslide from the upper part to the lower part of the slope. 3-D simulation shows that debris flow moves down to the bottom of mountain slope with a speed of 7.74 m/s and may make damage to the tunnel portal directly after 10 seconds from slope failure.

Simulation and Analysis on Slope Cutting Reinforcement Scheme of Lishigou Tunnel

In the construction and excavation process of highway project in mountain area, because the value degree of the geological environment conditions and geological disasters is insufficient, so it often causes the landslide resurrection or part of the resurrection, and forms a new landslide disaster. To ensure the tunnel portal construction and the stability of the slope, this paper based on LiShigou tunnel portal slope engineering, in view of the different slope unloading plan of the LiShigou tunnel portal slope, and based on FLAC3D software to take numerical simulation analysis and comparison, then to determine the safety and the reliability of the construction,at last the optimum scheme of the unloading is choosen.

Analysis of Nonlinear Seismic Response and Stability for Tunnel Portal Slope

The nonlinear seismic response of transverse slope at secund tunnel portal is first studied with dynamic finite element method under conditions of horizontal, vertical and both horizontal and vertical input, and then the dynamic safety factors of the most dangerous slide face which vary with time are researched after adding the field of static stress. For the purpose of dynamic stability evaluation, the total average dynamic safety factor and the permanent displacement are bring forward and used in this paper. At last, the model of dynamic response analysis and stability evaluation is built for transverse slope at secund tunnel portal.

Stability Analysis of Highway Tunnel Portal Slope in Shiyan Area

Under the control of the tow-Yun fracture, the geological conditions are complicated and the rock strata is broken in Shiyan area ,in the northwest of Hubei province, and the rock mass is weathered into fragment. When Highway is built in this area, a lot of tunnel portal slope and landslide problems will be met. To properly solve these problems, it is needed to analyze the slope stability and to propose appropriate management measures. In the paper, taken a highway tunnel portal slope in Shiyan area for example, a detailed research was made on the mechanism of landslide formation, and using laboratory soil test results and the simple Janbu method, the local and global slope stability is calculated. The results show that the slope is stable in natural state, and in heavy rains the stability coefficient is reduced quickly and the slope will be sliding. So the slope needs to manage and the rain water needs to control.

Assessment of the dynamic stability of the portals of the Dorukhan tunnel using numerical analysis

Instability problems may arise during the construction and operation of tunnels depending on the quality of the rock mass. In particular, determining instability problems at the portals of a tunnel is of utmost importance during excavation and operation of the tunnel. Slope instability and rockfalls are the most frequent instability problems that may be encountered at tunnel portals. Such instability problems can be triggered by dynamic effects such as earthquakes, blasting, etc. This study investigates the stability of the portals of the Dorukhan Tunnel connecting the provinces of Zonguldak and Bolu in the close vicinity of the North Anatolian Fault Zone (NAFZ), which is a well-known strike-slip 1500 km long fault. The effect of an earthquake that may occur in the NAFZ on the extent of failure has also been studied by numerical analyses. In the analyses, a three-dimensional dynamic analysis computer code, based on the finite difference method, has been used. According to results of the dynamic numerical analyses, the Devrek portal was found to be more stable than the Mengen portal. Moreover, it was found that, for acceleration values of dynamic wave higher than 0.5 g, tunnel portal slopes and the areas as far as 20–50 m from the tunnel entrance may suffer serious damage. Wave propagation perpendicular to the tunnel axis was established to cause more damage around the openings and in the portal slopes as wave compared to propagation parallel to the tunnel axis.

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

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

Evaluation of Seismic Performance for Tunnel Retrofit Project

A seismic retrofit program at Yerba Buena Island Tunnel is presented as a case history. The studies include evaluations of portal stability under earthquake excitation and performance of the tunnel liner as a result of seismic induced deformation. Due to different potential failure modes at the two portal areas, two separate evaluation techniques were utilized. Key block theory in conjunction with a Newmark type analysis was used to assess movements of a potential failure wedge at the west portal slope, while discontinuous deformation analysis was utilized at the east portal slope to evaluate a rotational mode of failure. To assess the performance of the liner subjected to design earthquakes, a two-step analysis procedure was adopted. The first step was to compute seismic induced deformations of the tunnel subjected to seismic wave propagation through the island rock without the presence of the liner. The second step, not reported in this paper, involved imposing the deformations of the tunnel onto the structural liner through spring elements that accounted for interaction between the liner and the surrounding rock. From the studies, performance of the existing tunnel supports was found to be acceptable.

Endotoxin pretreatment enhances portal venous contractile response to endothelin-1

To test whether endotoxin pretreatment modulates the portal hemodynamic response to endothelin (ET)-1 and phenylephrine (PE), two potent vasoconstrictors in the portal circulation of the normal liver, rats received intraperitoneal injections of Escherichia coli lipopolysaccharide (LPS; 1 mg/kg body wt) or saline. Livers were isolated after 6 or 24 h and perfused with Krebs buffer containing 5% autologous erythrocytes. Analyses of portal pressure-flow (P-Q) relationships and epifluorescence video microscopy were performed before and after ET-1 (10(-9) M) or PE (10(-5) M) administration. LPS pretreatment increased total portal resistances (Rt), zero-flow pressures (PQ = 0), and linear regression slopes of P-Q relationships, and decreased the sinusoidal diameters (Ds) and sinusoidal volumetric flow (Qv). The response to ET-1 was enhanced 6 and 24 h after LPS administration, leading to greater increases in Rt, PQ = 0, and slope and more pronounced decreases in Dx, red blood cell velocity (VRBC), and Qv. In contrast, PE effects were similar (PQ = 0, slope, Ds) or even attenuated (Rt, VRBC, Qv) in livers from LPS-treated compared with control animals. Thus endotoxin pretreatment increased the portal contractile response to ET-1 but not to PE. This enhanced ET-1 response appeared to occur at sinusoidal and presinusoidal levels and may contribute to endotoxin-induced hepatic microcirculatory failure.