Abstract: Free oscillation test is a hydro-geological test which adopts excitation method to make an instantaneous change in borehole water level. Through the test process the water level-time response data will be measured and thus to determine the permeability coefficient of the aquifer stratum. This test has been applied in many engineering projects for stratum permeability evaluation and has an efficient result. Air pressure is usually adopted to excite the water head, while water injection is convenient to excite water head only by injecting a certain amount of water. It needs less equipment and operates easily. In this research we conducted a free oscillation test with water injection method to evaluate the stratum permeability coefficient and compared the advantages and shortcomings of various test methods (gas pressure and standard water pumping and injection). We found that free oscillation test with water injection method is the most convenient, however, some part of the test data revealed deviations rather than the results derived from the standard water pumping test. We analyzed the causes of the deviation and put forward improvements to demonstrate the feasibility of this test method with the expectation to verify the improved method and achieve popularization of this test method in hydropower station projects.

Key words: permeability coefficient, free oscillation test, water injection, excitation of water head, standard water pumping test