Evolution regularity of the plateau tectonic karst and the relevant karst groundwater circulation mode in Mount Genie and Zaya sections along the Sichuan-Xizang Railway

Construction of the Sichuan-Tibet Railway may face significant geological safety risks of water inrush and mud inrush in the plateau tectonic karst region. It is of great scientific and practical significance to carry out research on the evolution regularity of the plateau tectonic karst and the relevant karst groundwater circulation mode for the early prediction and identification of the water inrush and mud inrush disaster in the railway tunnel to be built. Based on the field survey and published literatures, this paper makes an in-depth analysis and draws some conclusions. The tectonic karst development shows obvious sequence characteristics and elevation zonation. The first level to fourth level karst development areas were formed before Miocene, late Miocene to Pliocene, Pliocene and Pliocene to Pleistocene, and occur in the elevation range of 4900−5300 m, 4000−4300 m, 3700−3800 m and 2900−3200 m, respectively. Active faults obviously control the distribution and enrichment of karst groundwater. Since the late Pleistocene, active faults have connected different karst areas and formed unique storage conditions for the tectonic karst groundwater in the plateau region. Karst groundwater system can be divided into high recharge area, remote pipeline flow area and concentrated discharge area. The high recharge area occurs in the first-level karst evaluation area, and the third-level and fourth-level are the concentrated discharge area which generally contain the outcropping springs with a discharge of more than 100 L/s. The groundwater system is appropriately divided into shallow and deep groundwater flow system. Karst springs are mainly supplied by ice and snow melting water, and exhibits the dynamic characteristics of the high water pressure, long flow path and deep water groundwater circulation. High CO₂ saturation concentration of the melting water and the salt effect of sulfate promote the formation of high TDS sulfuric acid karst groundwater of low temperature.