Kunming South Downtown Land Subsidence

According to the datum of the second grade leveling from 1987 to 1998, significant land subsidence was found in Kunming city. The south Kunming city is the dominating area of land subsidence, whose total area is 180 km2, and has formed two very prominence infundibular areas. The one is located in Guangwecun-Xiaobanqiao-Wujiaba airport, the other is around Yuhucun-Fuhaicun. The most prominence subsidence area is Xiaobanqiao center, which amounted to 236.2mm(from 1987 to 1998). What's more, the land subsidence is accelerating and expanding.In south Kunming city, stratum, lithographic characters, tectonics, geomorphology and neotectonism influence the groundwater's existence, distributing and seepage. Void water is affluent in the lake deposit void of Cainozonic, which has multiplayer structure, and is discontinuous. Karst water is affluent in carbonatite rock formation of Palaeozoic, which formation are abroad, thick, and watery. The Karst water is the most important type of groundwater in South Kunming, and its water level is fleetly falling in some areas where lies a great number of pumping wells. On the other hand, in South Kunming, the Quaternary soil is soft and clayey, stratum structures vary a lot, the engineering character of shallow soil is badness, and lacustrine-clay soil has marked anisotropy characteristic. In short, the hydrogeology conditions and the engineering geology conditions are vital geological factors, which influence the occurrence and development of land subsidence, and lead it to be what it is currently.Groundwater pumping, architecture loading, constructing, soil nature concretion and neotectonism are together playing an important role on land subsidence. Each complication has its connection with land subsidence: (1) Because the pattern of land subsidence in South Kunming is dislocation basin pattern, the interface between Quaternary soil and bed rock cannot separate ground water, so that the void water-bearing bed may communicate with karst water-bearing bed. Pumping karst water can render the concretion of Quaternary soil. Where the level of karst watermay communicate with karst water-bearing bed. Pumping karst water can render the concretion of Quaternary soil. Where the level of karst water falls a lot on the edge of basin, there is a prominence infundibular area. (2) With the city's expanding, architecture's consistency and cubage increase swiftly and violently, and the proportion of newly-built architecture is most. What's more, the engineering character of shallow soil is badness, all of the above magnify the architecture loading's effect on the land subsidence. (3) The infundibular area of land subsidence is located in the brim of lake basin, where is the area pristine Dianchi lake, and it is become land not long ago. The whole Quaternary Period lacustrine-clay soil is very soft, gravitational concretion is going on. On the other hand, lack peat's oxidation accelerates concretion. (4) In the investigative area, Neotectonism is activities, which straightly result in the land subsidence. Because different complication has different effect, and the dominant complication is not fixedness. This paper introduce fuzzy judgment and classified analysis to probe into all of the complication, and working-out their shares as follow, pumping groundwater account for 72%, and architecture loading account for 11%, and constructing account for 7%, and soil nature concretion account for 9%, and neotectonism account for 1%.At last, based on the mechanism of land subsidence in South Kunming, this paper has forecasted the extendecy of the land subsidence, and putted forward some preventive advice.