| The karst area of Yunnan Province is about 1.11×10~5km~2,accounting for about one-third of the total area of Yunnan Province;Most areas of Changshui Airport are located in karst areas,with strong karst development and complex tectonics.Paleozoic soluble rocks,such as carbonate rocks and clastic rock,are mainly exposed in this area.Carbonate rock accounts for the majority,and only partial clastic rock is exposed.Karst development is the main adverse geological process in the site,which is easy to cause uneven surface subsidence,karst collapse,soil deformation and other problems.Therefore,it is particularly important to identify the laws,characteristics,and mechanisms of karst development in the site area and guide airport construction,which has significant practical significance.This article comprehensively utilizes various methods,including on-site geological survey,engineering geological mapping,drilling,geophysical exploration,on-site testing,hydrogeological testing,and indoor testing.Based on the coupling data and the comprehensive analysis of previous research results,the physical geography and geological overview,engineering geological conditions,hydrogeological characteristics and engineering activities in the region have been accurately identified,the surface and underground karst morphology,scale,section,etc.of the site have been further studied,and the karst distribution law has been analyzed from the plane law,vertical zoning,fault control and other aspects of karst development.On the basis of in-depth analysis,qualitatively and semi quantitatively evaluate the stability of karst foundation in the site area,and numerically simulate the stability of karst cave surrounding rock based on the ANSYS numerical model.Through analysis and calculation research,the following conclusions and research results have been obtained:(1)The research area is located in the central part of the Yunnan Plateau,with the terrain being the second largest staircase in Yunnan Province,which decreases from northwest to southeast.The karst in Kunming area belongs to the karst area of the carbonate rock series from the Proterozoic to Mesozoic on the Yangtze paraplatform,which is a sub region of the karst plain Qiufeng Plateau in eastern Yunnan;This site belongs to the karst quasi residual hill area of the karst plain area,and the karst is generally relatively developed,mainly vertically developed,with less horizontal development.(2)The karst on the surface of the site includes karst depressions(approximately57,irregularly circular,elliptical,elongated,spindle shaped,etc.),sinkholes(2locations),stone teeth,karst ditches,and karst troughs.There are also underground karst areas within the site,mainly manifested as underground karst caves,karst fracture zones,and soil caves;Drilling revealed 174 underground karst caves and 2soil caves.(3)There are two main patterns of karst development:planar distribution(positive karst morphology and negative karst morphology)and vertical distribution(vertical karst pipeline vertical infiltration).From the perspective of plane distribution,karst in the site is mainly concentrated in areas with developed faults and folds,near contact zones of different lithology(near stratigraphic boundaries),and in areas where surface water collects runoff at the bottom of valleys(gullies).Karst is relatively underdeveloped in areas with steep terrain slopes;From a vertical distribution perspective,dissolution mainly develops in the aeration zone and strong horizontal seepage zone,as well as in the vertical infiltration zone and strong horizontal runoff zone(within the seasonal variation zone and a certain depth range below),and vertically infiltrates along the karst pipeline.(4)There are many factors affecting karst in the site area.It mainly includes landform,tectonics,stratum lithology and hydrogeological conditions.Among them,faults are the main controlling factors,and the Dajianshan Yangtaoqing Fault(F10)has a large scale,which controls the structural development of the engineering area,disrupts the continuity of the structure in the area,and controls the evolution of the structures on both sides of the north and south.The karst at the fault is extremely developed,and the karst space is extremely high.(5)Research on the mechanism of karst development and collapse in the site.The development mechanism is mainly constrained by lithology,F10 fault zoning,hydrochemical dissolution and mechanical energy,the closure of negative terrain,and the slope of the ground;Karst collapse is mainly caused by three types of actions:(1)changes in geological structure;(2)Rainfall infiltration;(3)The groundwater level has decreased;(6)Use ANSYS to calculate the stability of the terminal karst cave,select the zk332 borehole to expose a typical karst cave with a horizontal irregular shape,a large change in diameter,no filling,and apply column loads;Simulating 10 working conditions,it was found that the changes in displacement,stress,and strain were relatively small,almost ranging from mm to single digit MPa,and the karst in the site was in a stable state. |
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