Large slopes constructed during road or building construction contain a number of potential risk factors, and consequently they require a more detailed inspection. In Korea, large slopes more than 200m long and with a cut height of more than 50m have been designated as large-scale slopes for special inspections. The total number of large-scale slopes located on the national highways is 146 and their average lengths and heights are 329m and 64 m, respectively. The safety inspection for large-scale slopes consists of an assessment of their stability and condition and an evaluation of the level of damage and potential risk factors. The final safety rating for slope stability is determined based on these assessment results and the future plan for periodic inspection is decided based on the final safety rating. In this study the safety ratings for all 146 large-scale slopes were evaluated and the economic efficiency of operating the current inspection system was assessed.
As approximately 60% of the national land in Korea consists of mountainous areas, it is essential to form a cut slope or an embanked slope as a prerequisite to construction work in many cases. In particular, more cut slopes are being formed for road construction than for other construction work as these construction zones are long, with most passing through mountainous areas. Most road slopes are distributed along expressways and the national highway, and their number is increasing year by year.
Currently, Korea has 4789 km of expressways along which approximately 7000 slopes are distributed. In addition, there are 13,797 km of national highway, more than twice the length of the expressways that have 29,757 slopes, which is more than four times the number of slopes as on the expressways.
The Ministry of Land, Transport and Maritime Affairs has been operating the Cut Slope Management System since 1997 in order to prevent slope disasters on the national highway and to minimize any damage. A complete enumeration of the slopes on the national highway through the Cut Slope Management System was conducted and a master planwas established based on the result and is in operation. Continued observation of these slopes is required, but only 124 sites on which it is difficult to apply reinforcement methods remain under real-time monitoring.
Of these cut slopes, slopes more than 200m long and with a cut height of more than 50m are designated as large-scale slopes under the "SpecialAct on the Safety of the Facility", regular safety inspection and maintenance must be conducted. The Cut Slope Management System includes safety inspections of the large-scale slopes that are distributed on the national highway, which contributes to reducing the damage that can result from slope collapse and also secures the safety of roads through safety inspections and maintenance.