Abstract
In Japan, public works projects including dam construction projects now face a strong demand for cost reduction. Therefore, at lower-height parts of a dam, the foundation is generally composed of weathered soft rocks or unconsolidated sedimentary soft rocks. In such a foundation, when groundwater level is low, the seepage through the foundation becomes unsteady one. In this case, as for the method of evaluating the saturated permeability of foundation, long-term permeability test is one of the most effective testing methods. However, it is difficult to conduct many cases of test of this type, because this test requires high cost and long time.
In this study, we conducted saturated-unsaturated seepage analyses to simulate Lugeon Water Test (LWT) conducted in unsaturated soft rock foundation. The LWT is a multi-stage constant pressure water injection test, and the most common in-situ permeability test for dam foundations. In this analytical investigation, we made seepage analyses under various conditions with changing effective injection pressure, saturated coefficient of water permeability and groundwater level, to evaluate the influence of these conditions on unsteady seepage tendency of injection flow rate and stable flow rate. Based on the results, we proposed the method of estimating stable flow rate which is necessary to evaluate a saturated permeability from the results of field permeability testing in practically appropriate time. In addition, we applied this method to the results of long-term permeability tests in unsaturated foundation to verify the reproducibility of stable flow by using this method. As a result, the estimated stable flow rate was found to the measured stable flow rate with high precision.
