| Jiangshan is a main area of Zhejiang Province where karst collapse hazards often happened. The occurrence and development of the karst ground collapse has brought immeasurable potential safety hazard and property damage to people’s production and life, from a certain extent, while also restricting the city planning and construction in the late. However, although system research and analysis have been done on the status and distribution of karst collapse in the region, but study on karst collapse mechanism and prediction is far from enough and not conducive to formulate scientific and rational control measures. Therefore, according to the status and distribution of karst collapse in Jiangshan, this paper studies on the characteristics of karst, distribution, factors and mechanism of karst collapse and establishes the prediction and evaluation model of karst collapse susceptibility in Jiangshan. It is important for urban planning and development of Jiangshan and the prevention of geological disasters.Basing on reorganization and analysis of the collected material about basic geology, hydrogeology, engineering geology and karst collapse data, the distribution of soluble rocks, karst development law, characteristics of karst collapse distribution, factors and mechanisms of action of principal study area are given systematical study in this dissertation. Then, the prediction model of karst collapse susceptibility is established. The main achievements are as followings:(1) The distribution characteristics and factors of karst collapse are analyzed and summarized. Most of collapses are developed in alluvial terrace and dissolution plain. Distribution of karst collapse is controlled by the degree of soluble karst development and the main fracture. Almost all of collapses in the area where the karst ratio of drilling line is high are closed to the main faults. The overall distribution of collapse sites are same as the trend of main faults. Karst is mostly developed in area where the thickness of overburden is between 5-10 meter. Collapse is developed in the area where the bottom of cover layer is sand soil. According to the history and current situation of groundwater exploitation, and the time-space distribution of karst collapse, the research shows that 73 percent of karst ground collapse is caused by groundwater pumping and draining. The distribution of collapse sites is closely related to the frequent and intensive activities of groundwater (such as groundwater descend funnel), and 27 percent of that is caused by climate change and natural fluctuations of groundwater.(2) According to the characteristics and laws of karst development, groundwater stores and migrates in triple medium which is composed of pore, fracture and cavity. Therefore, the paper applies the seepage-fissure-pipe flow theory, the groundwater flow numerical model is established. The dynamic change in groundwater level were simulated and predicted. These lay the foundation for comprehensive prediction model of karst collapse considered the dynamic change law of groundwater.(3) The development law of principal study areas of karst ground collapse is studied. There are five grade Ⅱ factors which influence the development of karst ground collapse:the degree of karst development, thickness of overburden, the lithology at the bottom of overburden, buried depth of the groundwater level, groundwater hydraulic gradient. Single elements maps have been graphed and assigned to attributes. Different factors contribute to the influence of karst collapse could be confirmed by the attribute information of collapse site. By coupling between groundwater flow numerical model and the fuzzy comprehensive evaluation model, comprehensive prediction model of karst collapse considered the dynamic change law of groundwater is established. According to prediction results. The division of karst ground collapse susceptibility in the principal study area into four districts, including prone district, relatively prone districts, less prone district and stable district, is completed.(4) Suitability zoning of engineering construction is completed. There is a big risk of karst collapse in unsuitable districts. Ground collapse caused by human factors should be avoided in relatively unsuitable districts. Limestone and other coverage area have good stability in basic suitable districts. In suitable districts covered by intrusive rock and clastic rock, surface collapse will not occur. In poor suitability districts where parts of collapse have been occurred and karst is developed, is devised into 13 subregions and unsuitable for engineering construction. In the suitable region where is devised into 30 subregions, it has not risk to ground construction and is suitable for engineering construction. It is suitable for kinds of engineering constructions in suitable districts.(5) According to the characteristics and genetic mechanism of karst ground collapse development in study areas and combing with the suitability zoning of engineering construction, some ssuggestions have been given:extraction of groundwater in urban area is completely prohibited to prevent karst ground collapse. Exploitation of groundwater is limited in planning constructions area. The government should enhance the management to over-extraction of groundwater, in suitable districts of engineering constructions, living, educational institution, station, administrative agencies, hospital, land for commercial financial activities and major industry have priority. Such as Qianhu-Wudu-Daxidi, Dafudi-Wantoushe-Lutingyan,Chuantou on both sides of 46 provincial road, the east of Jiangshan port, Shishandi-Hejia-Shihuitan, Sanliting-Shuangtadi in the middle, Wumushan-Yangmeixikou-Gangfudi-Wailong-Petrochemical Works-Sanguangjiao in the east of Jiangshan port, Luchen-Hangfushan in the east of Tiger mountain, in the north Luchen-Tongjia, Guangtoushan-Xiajiayao, Zhujiafan-Daquanzui, Yecun, Maotang and Jitou. In recent urban planning, part of living educational institution, station, administrative agencies, hospital, land for commercial financial activities and major industry are in suitable and poor suitable districts. Such as Daxitan-Lijia, Old station-Huangchen, Luchen where is suitable for living of grade one and grade two, Pingtan-Gongbianyu, Hualuting-Nongkenchang where is suitable for industrial land of two and three types. Strengthening engineering geological and hydrogeological exploration is suggested. In constructions area, the scale and characteristics of covered karst, the nature of karst cave fillings and mechanical characteristics of rock and soil should be found out. In covered karst area, exploration depth should be increased. When the thickness of the Quaternary overburden is less than 30 m, exploration depth should be under the full bedrock 20 meter without karst cave. When drilling in karst cave, exploration depth should be under the complete bedrock at the bottom of karst cave 10 meter. When the thickness of Quaternary overburden is more than 30 meter, exploration depth should be under fresh bedrock 5 meter, Maodun-Zhaishang located at the south of middle planning area, Huchuantou-Wudu on the northern side, where is unsuitable districts of engineering construction. Planning and design should be scientific and reasonable in future.The main innovation points:Based on seepage-pipe flow theory, the coupled model of karst groundwater flow numerical model and comprehensive evaluation model of the karst collapse is established. The groundwater dynamic change is mainly considered in the processes of karst collapse predetermination. |
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