| With the development of the Western Development Drive and the Belt and Road Initiative in recent years, the demand of living environment, space and energy resources for people is increasing. Human behavior of building is necessary for social production and development, and now focus on space over the surface while gradually turning to more complex geological conditions in the western region, karst is one of the main manifestations in Southwest China’s complex geological environment.Topographic gradient of southern Sichuan Basin located in the transition region between the Sichuan Basin and Yunnan-Guizhou Plateau, cutting by the Yangtze River valley in the north, the topography is slow and low, south terrain gradually rises until fully completed topographic gradient "on stage " process when it near the Yunnan-Guizhou Plateau surface. The carbonate distribute widely in this region, the karst water resources also abundance. In recent decades, this region has become an important target of development, underground traffic engineering, shale gas and mine exploitation and utilization of karst water resources construction and development become more frequent. The research of karst water system has scientific significance for human activities for it is closely related to human activities.This paper based on the study of local railway, highway construction and water conservancy, mine geological environment research in southern Sichuan Basin terrain gradient zone for the past decade, combined with the regional hydrogeologic information extraction, the use of hydro-geological surveys, geostatistical methods,isotope techniques, geochemical inverse modeling, three-dimensional numerical simulation technology and other means, from the point of view of regional groundwater system theory, a comprehensive analysis of regional karst water system,and achieved the following main results and conclusions:(1)Based on the features that the great terrain gradient and widely distributed karst in the terrain slope gradient zone between southern margin between the Sichuan Basin and Yunnan-Guizhou Plateau. With the 1: 50000 and 1:200000 regional geological data, statistics 3494 karst types in T1j+T2l, P1 y, D3+D2q, O1+O2 and ?2-3lsfive sets of karst formations, to summarize karst development characteristics and distribution law by the number density, scale morphology, evolution formation,location and direction of development and other factors, explored the karst development rule of this unique topography gradient.(2)By statistical data analysis, to summarize the law of karst from the intensity,distribution elevation and other aspects divided karst development degree into strong,medium and weak three regions, the strong development of karst formation is P1 y and T1j+T2l, the medium developmental of karst is D3+D2q and O1+O2, weak development of karst formation is ?2-3ls; The distribution of karst elevation has obvious ladder zonation, in the five stages of elevation: 1950~2200m, 1500~1800m, 1000~1300m,700~900m and 300~600m has distribution 93.3% of the karst type, which divide the karst region into five karst gradient zone.(3)The region belonged to three major tectonic units, the Chishui concave fold bundle in east Sichuan trap fold bundle of Sichuan platform downwarp in Yangtze paraplatform, the junlian oncave fold bundle upper in southeast Sichuan platform downwarp of Yangtze paraplatform and the northeastern Yunnan fold bundle in the northeast of Yunnan station platform fold belt. The structural system is complex,therefore, according to geological, lithology and boundary conditions, combined with regional structural features. To divide this area into 5 geological unit regions which named NE trending geological unit, EW trending geological unit, SN-EW recombination trending geological unit, NE-NNE trending geological unit and NE trending rotational shear geological unit.(4)The reasearch area has T1j+T2l, P1 y, D3+D2q, O2+O1mb, and O1t+h+?2-3ls carbonate rock layer groups which can be divided into pure layer type, interlayer and mixing layer type according to the purity and thickness of the rock layer. Combined with the karst development intensity, occurrence factor and geologic structure, the structures of carbonate rock aquifer groups can be classified into monocline type,anticline type, syncline type and fault type, 38 karst hydrogeology structures.Meanwhile, space partition of every hydrogeology structures is implemented within 5geologic units.(5)The karst water in the research are divided into 2 types, conduit type and fracture type in terms of differences between 2 occurrence media. According to the combination features of media forms, the media structures can be classified into pure layer conduit-fracture type, interlayer conduit-fracture type, pure fracture type,interlayer or mixing layer fracture type and fracture-pore type. The water abundanceof the karst aquifer structure depends on the media type. Combined with structural geology conditions, karst structure with abundant water mainly includes fold type and fracture type and also includes monocline type, discharging into river valley type and lithologic varying zone type.(6)The research area has well-developed surface water system and it can be divided into Guan River(I-1), Nanguang River(I-2), Changning River(I-3),Yongning River(I-4) and Chishui River(I-5)the first hydrogeological units, each of which are all regional systems, dominating the runoff and discharge of the groundwater. Meanwhile, the regional karst water system can be divided into large karst spring system and underground river system. Among them, underground flow conduit system in underground river system is well-developed in the research area and it can be divided into single step type and multiple steps type in terms of its flowing features.(7)The underground rivers of the area have also shaped the development of dendritic morphology except for single pipeline, which has multiple source with absorbing the flow characteristics of karst water system, more reflecting the complexity of the underground river system. In view of this, in order to clearly identify the flow process of the underground river system, the paper selects Xunsi town of Junlian Xiaoyudong and Liangfengdong’s underground river systems and underground deep circulation hydrothermal system to simulate of hydrogeochemical path in, for determining the relationship between the deep karst water flow system. In addition, the paper, based on the isotope elevation effect, has carried on the qualitative analysis of karst water flow rate.(8) According to China Geological Survey’s classification criteria of karst water system. The regional karst water system is divided into 2~4 based on level relationship. Among them, according to the minimum standard, study area developed a total of 1235 karst water system. On the side, the paper research five types of hydrodynamic circulation zoning characteristics of water-bearing structure, which are single pure rock stratum type、pure rock stratum type+Overlying non-carbonate rock stratum、pure rock stratum type+underlying non-carbonate rock stratum、pure rock stratum type+lateral distribution of non-carbonate rock stratum and the sandwich type or the alternating layers type of inter form. Combining with regional hydrodynamic conditions, the karst water circulation system is divided into 5 kinds of patterns which are monoclinic type, anticline type and syncline type, fault type and buried type.Meanwhile, according to the different patterns of circulation hydrogeological partitionis made for the regional karst water system.(9)The paper researched the interactions between human activities in southern Sichuan and karst water system environment. Taking the project of traffic tunnel as an example, paper used numerical simulation method to evolve the impact process for providing the future human engineering activities detailed and reliable geological basis. At the same time, the research can also supply reference value for protecting and rationally developing the natural characteristics of karst water resources. |
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