Application Of GIS For Risk Assessment Research Of Karst Subgrade Diseases Along Highway

At present, GIS has been widely applied to the risk assessment of all kinds of geologic hazards, but most of them are regional. It is still few that GIS used to assess the risk of geological hazards of large-scale land for lifeline such as highway construction. For this reason, the paper discussed the theories and approaches of risk assessment of karst subgrade diseases in land for highway construction using GIS, taking the No. 4 section of Shuiren-Nanning Highway for example. In this thesis, karst subgrade diseases have two meanings: one is the deformation, destroy and failure of the subgrade caused by karst process, another is the karst features that have bad effect to the stability of the subgrade.The contents of the thesis include:1. The construction of database of karst subgrade diseases in Shui-Nan Highway2. The types, endangers, development and spatial distribution characteristics, and triggering mechanisms of the karst diseases along the highwayTypes and numbers of the karst diseases have been analyzed through field survey and history data obtained, and then the development characteristics and triggering mechanisms have been shown using GIS. The results show:①The most developed section of karst diseases is GK203+621～K205+104 with the type karren, doline, sinkhole and cave, and K208+943～K209+769 with the type karren, sludge, sinkhole and cave.②The distribution of the karst diseases is very clustered. 50% of the disease points are less than 90m away from their nearest neighbors, 80% less than 202m and 90% less than 300m.③The karst subgrade diseases are almost nature formation: the location is karst valley with karst well-developed in land form, the depth of the overburden soil is 0~20m, subterranean streams are well-developed, variation of underground water table is larger and a normal fault across the highway exists. Subterranean stream is the first factor controlling the development of the karst diseases along the highway and normal fault is the second.3. Risk assessment of the karst subgrade diseases along highway using GISFirstly, deciding the weights of the karst diseases and their affecting factors using the AHP and building the risk assessment model of karst subgrade diseases, then assessing the risk of the diseases quantitatively using GIS. The results of assessment show that GK203+802～K204+962 , K205+870～K205+998 and K209+110～K209+624 are very high risk which is 1.909km, about 15.1% of the total length. High risk is 1.784km, about 14.1%. Moderate risk is 2.496km, about 19.8%. Low risk is 6.456km, about 51.0%. Risk assessment has been carried out quantitatively, which is prior to qualitative assessment.