Study Of Defining Tunnel External Water Pressure With Hydrogeochemical Method

With the development of science and technology, various tunnel projects develop quickly in the world, the high external water pressure and flow are the most important problems faced in the tunnel design and construction.At present there are two methods can be used to define the high external water pressure. The first is the function coefficient method of external water pressure; the second is the analytical method of rock seepage field. Concentrating on the questions of high external water pressure and flow of tunnels, author analyzes and studies in detail with hydrogeochemical method, poses a new method to define external water pressure. The Fundationals as follows:Correlation between CO2 pressure and hydraulic head is studied. In the same geological unit CO2 pressure in water is linear correlation to hydraulic head, Based on the correlation and the tested tunnel CO2 pressure can indirectly lead to external water pressure.The paper introduces a method to measure the total CO2 in the groundwater quickly - gas sensitive electrode method. According to the theory of carbonate balance based on activity, can calculate the HCO3-'s percentage of total CO2, then with pH value define CO2 pressure.It is practical for this method to two examples of ChenCun hydropower station and JuRong pumped-storage power station, and hydrogeochemical method of defining external water pressure be testified to be correct.