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.

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The present states of picoplankton were surveyed in 41 Japanese reservoirs of which nutrient level varied from oligotrophic to eutrophic. Based on the results, the effects of nutrients and artificial circulation were investigated. In all reservoirs surveyed, we found occurrence of picoplankton. Summer average cell numbers ranged from 2,800 to 518,000 cells/mL. In the conditions of T-P level from 10 to 60µg/L, summer and thermocline, cell numbers of picoplankton were abundant. In the reservoirs artificial circulation installed, the abundance of picoplankton tend to decrease to half level compared to no circulation reservoirs. Based on the results obtained, future managements policy of dam reservoir was discussed.

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Seismic waveforms of the 2011 off the Pacific Coast of Tohoku Earthquake recorded at the base of a dam site in Fukushima prefecture are analyzed comparing bore-hole motion records of KiK-net, and are reproduced based on the empirical Green's function method. Three empirical Green's functions are prepared to five strong-motion-generation-areas (SMGAs) model by the records at minor earthquakes, considering the spread of the fault area. Nearly simultaneous arrivals from SMGAs at off-shore Miyagi prefecture and off-shore Fukushima prefecture contributed to the maximum acceleration value at the target site.

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Application of Electrical Resistivity Tomography (ERT) to quarry site bedrock above groundwater level at the Oyama dam and its evaluation are discussed in this paper. The method contributed to supplement boring investigation data, and to complete information acquisition on: geological features; distribution of targeted materials at the quarry site; and its quality. The Andesite is selected for aggregate of which concrete is produced for the dam. The rock is hard but with multiple cracks. At the beginning of excavation, it revealed that the bedrock in shallow part is not suitable for aggregate, and that it is required to conduct further investigation of the quarry site and revise the mining plan without delay in the project schedule. Groundwater was not found in the bedrock. To apply ERT above the groundwater level, water has to be filled in the boring holes. However, it was not possible due to geological features at the site. ERT was improved to meet the requirement. Filling the bubble in the holes was tested, and the investigation was successfully completed.

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Horizontal construction joint between new and old dam-concrete is likely to be a structural defect that endangers security and water tightness of the dam body. In this study, simple flexural strength tests by cylinder specimen that commonly used to compressive strength tests are executed to find the factors playing into the horizontal construction joint such as green cutting and curing methods for old concrete and properties of bedding mortar. Results show that the flexural strength of horizontal construction joint after long-term interruption is lower compare to the immediate placing case.

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