Research On Groundwater Limiting Emissions For Mountain Tunnel Based On Ecological Water Demand

There are varieties of mountains in China. Road and railway constructions of different levels need to pass a variety of high mountains inevitably. Many of them are high-pressure and water-rich mountain tunnel. In the past, in most cases, groundwater treatment measures during the process of mountain tunnel construction using exclusive principles, it is inevitably undermine hydrology of the tunnel site. On the one hand, it may impact the stability of water-rich mountain tunnel lining and surrounding rock. On the other hand, it may lead to excessive inflow of tunnel site, level dropps of earth's surfice, environmental degradation and other adverse effects. In this paper, in order to maintain the ecological demand of water tunnel project and stability, practicality, and durability conditions of the tunnel site, in the concept of taking positive measures to retain water and limited emissions to design tunnel, based on the Zhongliangshan tunnel of rail transit line 1 in Chongqing, theoretical analysis and numerical simulation analysis were used to study on groundwater seepage law related on emission limits mode of water-rich mountain tunnels. Put forward reasonable limits of tunnel discharge and proposed references for design, construction and waterproofing and drainage measures of water-rich mountain tunnel. The main contents and results are as follows:(1) After a review of relevant literature to understand determining water inflow methods for mountain tunnel. Based on the basic theory of Darcy's law, groundwater dynamics and seepage of groundwater fractured rock, derivate formulas of deep tunnel inflow and lining water pressure. Based on vegetation ecological water protection needs, determine the maintenance of vegetation under favorable growing conditions. Determine tunnel discharge calculation method to determine a reasonable limit emissions and methods for external water pressure of lining under limited discharge mode. Collate and analyze the tunnel design criteria under “ecological water protection”.(2) By the hydrogeological survey data of Zhongliangshan Tunnel engineering, using numerical simulation, establishing seepage model during construction stage of montain tunnel under fluid-structure coupling. Analyze the seepage impact in Zhongliangshan tunnel for the stability of surrounding rock and lining structure, groundwater inflow, variation of groundwater level. Establishing the tunnel seepage flow model under grouting conditions to simulate the seepage influence of the excavation process. Get the influence of tunneling seepage in grouting conditions.(3) Considering different various factors, including different drainage patterns, precipitation, rock classification, permeability of initial support, permeability and thickness of grouting circle respectively. Studying the seepage law on tunnel construction phase and operate phase. Analyzing variation of water inflow, water pressure of lining, groundwater level changes with the variation of various factors. In order to provide references of limiting emissions of groundwater discharge mode.(4) Analysed the influence of different thickness and permeability coefficient of reinforced zones on the seepage field and stress field and displacement field and stability of the reinforced zone and initial support structure and the secondary,obtained the distribution regularity and change characteristic of the Seepage field and stress field and displacement field of the the reinforced zone and initial support structure and the secondary and the stability of the secondary lining,also obtained the reasonable design value of thickness and permeability coefficient of reinforced zone.(5) According to hydrogeological and precipitation of the tunnel site, calculate the allowable emission of different rock classifications and different seasons under the ecological conditions of the tunnel. In this emission control, combined with anti-hydraulic tunnel lining structural design requirements and the amount of the tunel inflow, propose groundwater treatment design program of tunnel construction and limited discharge implementation methods based on ecological water demand protect, give a groundwater discharge reference value for Zhongliangshan tunnel.