| Karst development has become the hot issue for many scholars,because the complex engineering hydrogeological conditions and fragile ecological environment which has been spawned in the karst development restrict the sustainable development of economic construction and karst ecological environment.In the high-steep anticline area of East Sichuan,the stripped distribution of soluble rocks alternated with non-soluble rocks,the steeply inclined structure planes have been developed,and the river traverses the high-steep anticline.In the period of neotectonic movement,,the intrenched rivers have promoted the deep circulation of karst groundwater,and the different parts of striped karst system have shown different characteristics of karst development due to their different adaptability to the discharge datum planes.The high-steep anticline mountains of East Sichuan seriously hinder the development of regional economic construction,and the traffic constructions have passed through the high-steep anticlines mainly in tunnels.In such a complicated karst geological background of the high-steep anticline in eastern Sichuan,the constructions of tunnel have encountered various problems of hydrogeology and engineering geology,and seriously damaged the fragile eco-geological environment.Therefore,a systematic studying on the spatial differentiation characteristic and mechanism of karst development and constructing the evaluation system of karst development based on the unique karst hydrogeological conditions of the high-steep anticline areas in East Sichuan has great significance to the sustainable development of economic construction and karst ecological environment.Based on the karst hydrogeologic conditions of the high-steep anticlines in East Sichuan,the paper firstly refined the types of karst system and deepened the uniqueness and diversity of various types of karst systems.Secondly,the spatial distribution of karst landform and its response to drainage datum plane were studied by using Hypsometric Integral,Hierarchical Clustering Method,and Depression-Overflow Method.Through the quantification of borehole data,analyzed the spatial differentiation of karst water-bearing media,and revised the classical theory of karst vertical zoning.Thirdly,based on the development characteristics of multi-level drainage datum planes,the coupling relationship of multi-level groundwater circulatory system in the interbedded carbonatite karst system was analyzed.Beside these,the paper further analyzed the differentiation of karst system and the coupling relationship of multi-level karst sub-systems.Finally,through a comprehensive analysis of the influencing factors of karst development of the high-steep anticline areas in eastern Sichuan,a fuzzy comprehensive evaluation system for the spatial variations of karst development was constructed and evaluated the spatial variations of the karst development in the northern section of the Guanyingxia Anticline.Through the above research,we have obtained the following main conclusions:(1)Based on the vertical superposition relationship between soluble and non-soluble rocks as well as the mineral characteristics of soluble rocks,the soluble rock stratums are divided into interbedded carbonate karst formations,pure limestone karst formations,and impure limestone karst formations.According to the characteristics of karst groundwater circulation,it is divided into shallow circulation mode,multi-stage mode,deep circulation mode,pressure-artesian mode.According to the combination between karst formation and groundwater circulation mode,the karst system is divided into pressure-artesian-interbedded carbonate karst system,shallow circulation-interbedded carbonate karst system,Shallow circulation-pure limestone,shallow-circulation-impure limestone,Multi-level circulation-interbedded carbonate karst system,multi-level circulation-interbedded carbonate karst system,multi-level circulation-impure limestone and deep circulation-interbedded carbonate karst systems.(2)The adaptability of the karst system to the drainage datum plane has been reflected in the spatial variation of the karst landforms.The karst landform units in the upper-middle reaches of the karst systems are mostly in the young stage or middle-old stage which belong to the last evolution cycle.However,the karst landform units on both sides of the valleys have better adaptability to the rivers.In the interbedded carbonate karst systems,the landform units on both sides of the valley are mostly in mature or young stage.The pure limestone and impure limestone karst system have poor adaptability to the transverse valley and been in juvenile stage.From the watershed to the valley,the karst landform types transit from I-1 type(monadnock-karst basin)to III type(peak cluster-karst valley).From the watershed between the transverse gullies to the gullies,the karst landform types transit from I-1 type(monadnock-karst basin)to II type(karst hill-depression).In the upper-middle reaches of karst system,the depressions are shallow in depth and large in area,they usually convert into karst lake.The small karst depressions and ponors are gradually developed in the near transverse gully.In the middle-lower reaches,the depth and scale of karst depressions are increasing in the direction of the valley.(3)under the background of the drop of the discharge datum plane,the development of karst water-bearing media shows the law of headward and lateral expansion.From valley to the watershed in the interbedded carbonate karst system,the probability that the drills come across the dissolved pores decreases with depth,and the proportion of dissolved holes in debris filling and no filling reduces,while the proportion of the dissolved pores in the chemical filling increases.The karst development of the pure limestone and the impure limestone karst system develops into the deep slowly,and the karst development decreases with the depth obviously.Based on the spatial variation of karst water-bearing media and the difference of hydrodynamic characteristics,the classical karst vertical zoning theory is revised,and the karst hydrodynamic forces are vertically divided into vertical infiltration belt,seasonal variation belt,shallow saturation belt,pressure saturation belt and deep slow-flow belt.(4)The coupling relationship of multi-level groundwater circulation system is indicated by the spatial relationships of different levels of rivers in interbedded carbonate karst system and characteristics of the transverse gullies.In the karst system of interfluve between Huaxi and Jiantuo river and that between Yangtse River and Yulin river,the groundwater circulation systems of transverse gullies have been inflected by the local groundwater circulation systems of transverse valleys most seriously,and yet the karst system of the southern Xihe and the northern of Wentang river is the weakest.Under the influence of multi-level drainage datum plane,the karst development which is into deep transit from cluster development close to valleys to uniform development.Besides,the development of the transverse gullies restrains headward extension of the karst subsystem of transverse valley.Whereas,the development of the latter captures that of the former.According to the coupling relationships of groundwater circulation system,the karst system can be divided into transverse gully type,deeply incised valley-transverse gully type,transverse gully-deeply incised valley and deeply incised valley.(5)Based on the analysis of the influencing factors of the spatial variation of karst development,a multi-level evaluation index system of karst development was constructed.The indicator system includes rock solubility,geological structure conditions,and dissolving dynamic.The rock soluble criterion layer includes rock type,layer thickness,and rock structure.The geological structure criterion layer includes fault,bedding surface,and formation dip angles.The dissolution dynamic criterion layer includes hydrodynamic vertical belt and hydrodynamic horizontal zone.The weights of different levels of evaluation indexes were determined by the AHP method,and fuzzy mathematics theory is used to quantify the evaluation indexes and constructed a fuzzy comprehensive evaluation system of the degree of karst development in the geographical information system platform.(6)The northern section of interfluve in Guanyinxia anticline was chosen as the study area to evaluate the spatial variation of karst development.The west wing of the anticline is affected by Baimiaozi fault,and the karst development index is significantly higher than other structure location of anticline;From the watershed to the Jialing River valley,the karst development index increases;The interbedded carbonate karst formation has the highest karst development index,the impure limestone karst formation has the lowest one.With the elevation falling,the karst development index decreases gradually.However,the karst development index of interbedded carbonate karst formation in the western anticline reduces less than the eastern wing due to the influence of Baimiaozi fault.By comparing the evaluation results and the karst phenomena which were revealed by the tunnels that have been built and under construction,there is a good consistency between them,which provides a scientific basis for the construction of following tunnel projects. |
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