Karst Water System Analysis And Its Suitability With The Tunnel Engineering In The North Of Huangling Faulted Dome

The area between Huangling faulted dome and Shennongjia dome is composed of massive carbonate rocks which belong to Sinian, Cambrian and Ordovician. The proposed high-speed railway starting from Zhengzhou to Wanzhou which connects southwest area with central, north and northwest China passes this region. Karst geology and karst water problems are the key points of engineering-hydrogeological problem to control the regional tunnel engineering, these problems play the decisive role of the railway's route scheme. Therefore, it is necessary to carry out the research of karst water system analysis and its suitability with the tunnel engineering in the north of Huangling faulted dome, which has realistic meanings.Based on the detailed investigation data, the studying area karst water system is divided and the feature of the system is discussed by using groundwater system theory. Then, this paper also analyze the tunnel-engineering suitability by importing GIS technique, taking the two route schemes of Xingshan-Baokang section of Zhengzhou-Wanzhou high speed railway as the study object. The main conclusions of the study are as follows:(1) The main emergence stratum in the studying area is dissoluble stratum consisting of Sinian, Cambrian and Ordovician, which can be divided into three bed sets:(1) upper Sinian(Z2), including Dengying formation(Z2dn) and Doushantuo formation(Z2d);(2) lower Cambrian-lower Ordovician(?1-O1), including Cambrian Shilongdong formation(?1sl), Tianheban formation(?1t), Qinjiamiao formation(?2q), Loushanguan formation(?2O1l) and Ordovician Nanjinguan formation(O1n), Fenxiang formation to Guniutan formation(O1f-O2g) stratums;(3) middle-upper Ordovician(O2+3), including Baota formation(O2b), Linxiang formation(O3l). Among them, Z2??1-O1 stratums are widely distributed and have relatively stable lithology and thickness.(2) Among the dissoluble stratums of upper Sinian(Z2), Dengying formation(Z2dn) has the middling water yield property, Doushantuo formation(Z2d) has weak water yield property; Among the dissoluble stratums of lower Cambrian-lower Ordovician(?1-O1), Cambrian Shilongdong formation(?1sl), Tianheban formation(?1t), Qinjiamiao formation(?2q), Loushanguan formation(?2O1l) have strong water yield property, which the karst strongly developed. The space in water-bearing medium is mainly dissolved-fissure to pipe network. Ordovician Nanjinguan formation to Honghuayuan formation(O1n-h) and Guniutan formation(O2g) stratums have middling water yield property, while Dawan formation(O1d) has weak water yield property. The karstification is middling developed in middle-upper Ordovician(O2+3) that have middling water yield property, and the space in water-bearing medium is mainly dissolved-fissure to karst cave network.(3) The karst water flow in studying area is controlled by Yangtze River and its branches: Xiangxi river, Huangbai river and Ju river. And Xiangxi river basin, Huangbai river basin and Ju river basin respectively covered the study area of 1052.23 km2?1388.13 km2?1131.76 km2, the soluble rock stratum distributed area covered 76.3 %?72.3 %?73.6 % of the whole basin area. Groundwater in the three basin is mainly carbonate karst water.(4) Considering the control of river network to the karst water circulation, we divide the studying area into north shore of Yangtze River karst water system(?), Huangbai river karst water system(?), Ju river karst water system(?), Xiangxi river karst water system(?), four first class karst water systems in total. Then according to the secondary basin surface watershed and regional water-resisting geological structure, we divide the first class karst water systems into 9 secondary karst water systems: west wing of Huangling anticline karst water system(?-1), east wing of Huangling anticline karst water system(?-2), Xiema-Ju river karst water system(?-1), Maliang-Ju river karst water system(?-2), Longkou river karst water system(?-1), Yaojiagou-Xiangxi river karst water system(?-2), Xingshan-Xiangxi river karst water system(?-3), Gaolan river karst water system(?-4), Qilixia karst water system(?-5).(5) Using GIS spatial analysis and overlay analysis functions to partition the tunnel-engineering suitability: the engineering suitability level show as bad, middling and well respectively covered area of 602.47 km2?1044.19 km2?795.46 km2, about 25 %?43 %?32 % of the carbonate exposed area. According to the GIS statistic analysis, it shows that the route scheme which would cross Xinhua is obviously better than the route scheme crossing Huazhuang between the two route schemes of Xingshan-Baokang section of Zhengzhou-Wanzhou high speed railway, except that Xingshan tunnel will inevitably cross the Yaojiagou syncline reservoir structure and the engineering suitability is bad. In the scheme 2 crossing Xinhua, the tunnels mainly locate in the midding to well suitability region.(6) After analyzing the interact relation between karst water environment and tunnel engineering and comparing the tunnel-engineering suitability, combined with the GIS evaluating results of tunnel engineering suitability, we draw the following conclusions: the scheme 2 crossing Xinhua is better than scheme 1 crossing Huazhuang. Scheme 2 avoid the large area of strongly developed karst region and syncline reservoir structure, which can lower the risk of high pressure karst water inrush, environmental damage and construction period investment into low-medium grade.