| In recent years, karst collapse has become a major geological environment issue in karst area. With faster urbanization and human activity increasing in China, the karst geological environment issue is growing by human, especially the large-scale construction activity, it changed the original formation mechanical balance, resulting in karst collapse events. Wuhan is a major city in middle China, karst bands are well developed. In recent years, urban construction in Wuhan is rapidly developed, leading to frequent incidents of karst collapse, resulting in loss of life and property, limiting the development of Wuhan. In this context, Wuhan need karst collapse geological disaster risk assessment, in order to provide geological basis for the Wuhan City Planning.In the paper, we use AHP for risk assessment in a district of Wuhan, divide susceptibility, danger, vulnerability and risk assessment rating.First, in the system analyzed research status on the basis of karst collapse,we carried out 1: 50,000 karst collapse investigation, including the history karst collapse events(time, place, scale, cause analysis, losses etc.),comprehensively analyzing hydro-geological conditions and engineering geological conditions, geophysical exploration test, drilling and other work.By analyzing the karst collapse events in the study area, we summarize the causes. They can be divided into geological factors and predisposing factors. Geological factors include the strong karst development degree,”upper clay and lower sand” dual structure and frequent water into three forms; predisposing factors are mainly natural and human factors, natural factors are mainly precipitation(short-term or continuous heavy rainfall precipitation), human factors are mainly the construction and the pumping wells. It is worth noting that since 2000, the collapse event in Wuhan mostly caused by the construction.On the basis of karst cause analysis, we select evaluation factor establish AHP model. To the susceptibility assessment process,we select karst conditions, Quaternary soil depth, Quaternary soil structure, karst water level fluctuations, Enrichment of Water in Quaternary water-bearing formation, fault and collapsed points as evaluation factors; danger assessment is prone on the basis of susceptibility assessment, additional considerations induced conditions, namely construction and pumping wells; for vulnerability assessment, select the population density and land-use planning as the evaluation factors. In the evaluation process, we select level of 3.5 to 5 as high-grade, 2.5 to 3.5 as middle-grade, 0 to 2.5 as low-grade, 0 as none-grade. Finally, risk assessment can be done.For each evaluation results,high susceptibility and middle susceptibity areas accounts for 32% of karst area and 17% of the total area,it can prove the geological conditions are relatively stable.After Adding predisposing factors, high danger and middle danger areas accounts for 64.29% of karst area and 34% of the total area, which indicates that even geological conditions are stable, coupling with predisposing factors, the risk of karst collapse is still high. High vulnerability and the middle vulnerability areas accounts for close to 50% of the total area, as the study area is in the main city.We get the risk result by combining with the danger and vulnerability zoning. High risk areas are in the Yangtze River, near the subsidence area, the pumping wells and the areas are 16.21km2, accounting for 6.45 of karst area and 3.41% of the total area.Middle risk areas are in the north around Tangxun, mostly around risk Liufang Street and the areas are 106.14km2, accounting for 42.22 of karst area and 22.33% of the total area.Low risk areas are mainly located in the western, southern and central areas and the areas are 129.05km2, accounting for 52.33 %of the karst area and 27.15% of the total area.Nnon risk karst area is risk-free areas. High risk and the middle risk areas accounts for close to 50% of karst area and around 26% of the total area,An area of high risk areas and risk areas and has accounted for about half of the karst area, and about one third of the total area, which requires us to be in attention the process of urban construction.Risk assessment results have very important implications for urban planning and construction in Wuhan.In the high risk areas, we need to avoid large-scale construction projects; At the same time, these areas should be monitored, early warning, as far as possible when the collapse occurred, losses to a minimum. |
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