As for rockfill dams with central clay core, many case studies have shown that onset of earthquake-induced sliding is insignificant for ultimate stability of the dams. To date, however, most procedures to evaluate earthquake stability of the dams have placed main focuse on the onset of the sliding. On this basis, this paper aims to improve the earthquake stability assessment of the dams.
According to various experiments, dynamic failure process of the dams consists of three steps: 1) small sliding and rocking motion of unstable rockfill material on a slope surface, 2) intermittent sliding of the material syncronized with the base motion, and 3) exposure of the top of the core due to accumulated sliding and settlement of the rockfill material followed by fatal cracks on a side wall of the core. While the step 2) is evaluated by the current procedures, the step 3) is regarded as the ultimate state of the dams. Based on a Newmark's model, the earthquake-induced rockfill sliding was calculated using two strong motion accelerograms. The results suggested that, when the sliding might exceed lm or so, it would induce total failure of the dam. The evaluation of this kind was found to be simple in calculation and practical in application.

View full abstract

Stiff clays and mudstones deposit around the world and give rise to numerous stability problems in slopes and foundations. These materials soften with time due to water absorption upon unloading resulting in strength deterioration. Weathering and slaking also contribute to softening through structural disintegration. This paper discusses the timedependent strength deterioration and its influence on stability of a cut slope. The process of strength deterioration due to softening is expressed in terms of a time-dependent yield surface. A finite element analysis is presented of accounting for strength deterioration due to softening. An example of stepped excavation is computed. The development of deformations and the progress of yielding were traced up to the collapse of the slope. It is shown that initial stress has a significant influence on the displacement and yielding behaviour of the slope. An effect of strainweakening on behaviour of the slope is also noted. Time-dependent deformations due to softening should be distinguished from those associated with conventional creep mechanisms. Importance is emphasized of properly understanding instabilizing mechanisms operative in field.

View full abstract

The variation of the surface moisture content of fine aggregate has a large influence on the properties of concrete. Especially in case of RCD concrete whose unit water cotent is relatively small. It is therefore emphasized that the surface moisture content of fine aggregate should be well controlled.
This paper discusses the control measures of unit water content of concrete influenced by surface moisture content of fine aggregate. It is found that the method using Kalman Filter is well adopted to control the water content of concrete. The Moving Average Method is also well adopted in the practical sense.

View full abstract

This study is one of the studies sbout the rationalization of concrete materials used on RCD Construction Method from the viewpoints of effective use of materials and cost reduction of aggregate production. We have grasped the properties of concrete including fine particles of aggregate, which were collected additionally in dry condition on the process of dry production system of fine aggregate.
We have reported the properties of fresh concrete from the test results in the case where we used fine particles of aggregate as a part of fine aggregate.

View full abstract

Kazunogawa Project, a pumped storage power station with a maximum output of 1, 600MW is being constructed in the eastern part of Yamanashi Prefecture by the Tokyo Electic Power Co., Inc. (TEPCO). The lower dam for the lower regulating reservoir is a concrete gravity dam whose height is 105.2m and volume is 718, 000m³. As successfully applied to TEPCO's Sabigawa Dam, the RCD method is adopted too, with a lift thickness of 1m, which has been achived in recent other projects. The capacity of concrete placing facilities was decided to accommodate the lift thickness of 1m. The maximum size of coarse aggregates was determined to be 120mm based on various tests and examinations.

View full abstract