Geohazard characteristics and cause analysis of ground subsidence and deformation along national highway in Beijing

The k125~129 section of a national highway, constructed in 1950’s, is located above a major coal mining area in southwestern Beijing. There are several layers of mine coal beds in this area. Numerous working and abandoned underground coal mines are distributed at the two sides of the highway and even in the safety zone or underneath the highway. Consequently, this highway section has subsided and deformed owing to the coal mining. The k125+600~800 section is the worst damaged area. It has had the maximum accumulative subsidence of 4.0~4.5 m and displacement of 2.0~2.5 m respectively since the 1980s. Taking the k125＋600~800 section as an example, the research aims to develop an integrated and effective reconnaissance technique to establish the predominant cause of ongoing subsidence of the highway and to affirm the existence of coal workings and other cavities beneath the damaged highway.