STUDY ON VARIATION OF ROCK MASS PERMEABILITY WITH HIGH PRESSURE PERMEABILITY TEST

Usually, 1Lu is considered to be the standard of terminating anti-seepage grouting in conventional pressure permeability test for the engineering of water conservancy and hydropower. With the development of science and technology, many pumped storage power stations have been or will be constructed. Test data show that permeability of rock mass is smaller using the high pressure test than that of conventional pressure permeability test. But for hydropower project with high hydraulic head, if permeability of rock mass is still calculated using 《Water Resources and Hydropower Engineering Borehole Water Pressure Test Procedures》(SL31-2003), the standard of anti-seepage grouting can be improved due to the decrease of Lu values with the increase of water pressure. For the applicability of the formula under the condition of high hydraulic head, specific water absorption of high pressure is put forward. It is defined as the injection flux of unit length with the diameter of 75mm, test section length of 5m and designed hydraulic head. It is expressed as DK with the dimension of Lmin-1m-1. Also, according to the numerical model, the injection flux of test sections for rocks is calculated. The comparison of calculated and measured injection flux is conducted in a pumped storage power station. The results show that when the high water pressure(designed hydraulic head) is 4MPa, the accepted standard of terminating anti-seepage grouting is 2DK which is correspondence to 0.5Lu. Therefore, for different hydropower projects, the standard of anti-seepage grouting needs to be changed according to the designed hydraulic head, instead of 1 Lu.