A Comparison and Evaluation of Landslide Stabilization Methods (Case Study: The Landslide Occurred in the 194 km of Malayer - Kermanshah Railway)

Landslide is considered as one of the reasons of natural resources loss in mountainous areas, leading to sever property damages and casualties worldwide (Fele Gray et al., 2013: 228). According to the United Nations’ report, landslide damages in developed countries is as equal as 1 to 2 percent of their gross domestic product, GDP (Lerouil, 2006: 198). The most well-known natural factors affecting the landslide are rainfall, lithology, slope etc. (Talebi and Niazi, 2011: 66). Moreover, road-building is considered as an effective human factor in the occurrence of landslides (Kelarestaghi, 2002: 5). In a research on the spatial association between the occurrence of landslides and roads in the forest regions, Larsen and Parks (1997) revealed that road building will increase the effect of the landslide by 5 to 8 percent.
In spite of providing several methods regarding the stabilization of landslide by different researchers, there is no unified consensus. Ramezani and Ibrahimi (2009) stated that, unlike the landslides made by non-natural factors, it is not often easy to control the ones made by natural factors.
In the present study, considering the uncertainties about a convenient and practical method to stabilize the landslide occurred on the kilometer 194 of the railway Malayer – Kermanshah (located between Aran, Kangavar and Ahangaran-e Sahne village), first, the stability of the aforesaid landslide will be discussed. Then, the geometry of landslide in different states including the present slope (unstable), the slope with modified geometry (the proposed method in this study), the modified slope proposed by consultant engineer, and the stabilized slope by pile system is modeled in FLAC 3D software, considering soil characteristics determined by the soil mechanics laboratory. Besides, the results will be evaluated and compared in order to choose the most appropriate method for landslide stabilization.
Materials and In this study, stability of a particular slope having different boundary condition has been modeled and analyzed using version 3 of FLAC 3D. In fact, geometry of slope was modeled in different conditions including unstable slop, slope with modified geometry (method proposed in this study), modified slope using proposed method by consulting engineers (Hexa Consulting Engineers, 2011), and stabilized slope using the pile systems (case studied in Malayer - Kermanshah railway). The soil characteristics were determined by soil mechanics laboratory. Moreover, the Mohr-Columb model, as the most practical model in soil slope modeling, was used. For the sake of validation, slope modeling was analyzed in Geoslope software version 2007 (limit equilibrium methods) in both natural and stabilized modes. Furthermore, the behavior of the progressive landslide was monitored using five stable monitoring points in different locations. The monitoring points were installed from bottom to the top of the slope which were mapped during four consecutive months, from September to December 2012, with ten-day intervals. Numerical findings were confirmed by comparing not only the consecutive mappings but also the latest and first mappings.
Slope analysis of the status quo proved the maximum displacement of 185 cm and a safety coefficient of slope stability of 1.26. High values of displacement marks the instability of the slope in this particular case. Slope modeling, after geometric correction, revealed a decrease in the displacement up to 71 cm, and an increase in the safety coefficient to 1.61. The proposal of the project consulting engineer suggested the slop adjusting and a concrete gallery implement to cross the railway track. In this case, the displacement in the gallery wall in the middle of the wall and the corners is 40-50 cm and 30-40 cm respectively, which may cause severe damages to the side of the gallery in case of landslide activity. Besides, the maximum displacement of the slope in this case is a bit more than 95 cm. In terms of stability safety, it should be noted that the maximum displacement in this case is less than 100 cm, so the amount of displacement is legal but on the edge of insecure borders. This condition can be soften by applying the procedures such as drainage. In the case of the pile application for stabilization, the largest landslide displacement was about 30cm, which was quite in a normal range, although it needs considerable operating expenses.
The findings of this study revealed that gallery implement method proposed by the project consulting engineer and stabilization method with piles are the most appropriate method for stabilizing the slope. The aforesaid method not only is economical, but also preserved the environment with the least interface in nature. Moreover, its safety and output are confirmed by the analytical model in FLAC 3D software. In the proposed method, geometric correction with drainage is cheaper, the displacement is lower, and the possibility of damage to the embankment is less. Moreover, in case of damage, it is easier to repair. Combining this method with Bio-engineeringmethods, such as planting of vetiver grass can increase the slope stability.