Most of the rock slopes have been designed with limit equilibrium and numerical methods, and the stability is expressed by Factor of Safety (FoS), which is basically a ratio between strength and stress. With this deterministic approach, design of slopes with careful consideration is still potential for the instability problems. Understanding on the probability of slope failure will give a significant contribution for safety operation and a probabilistic expression of the stability can be considered. In this paper, a statistical approach based on actual stable and failed cases of rock slopes is described. As the slope stability was only defined as stable or failed, logistic regression was utilised because the method is suitable for categorical dependent variables. The model prediction is close to the actual stability data, where the model predicts 17 out of 21 stable cases and 13 out of 16 failure cases.

View full abstract

The purpose of consolidation grouting for dam foundation is to improve the permeability and mechanical properties of rock masses. For permeability, the grouting effect is usually confirmed by the permeability test at check holes. But for the change of mechanical properties, it has been difficult of confirmation. Therefore, the mechanical improvement of foundation by grouting, like the changes of elasticity and strength, has not been considered in dam foundation design. In this study, in-situ experiments were made in order to examine the grouting effect on mechanical properties of rock masses.

View full abstract

A novel imaging method for the establishment of hydrogeological model of rock mass is proposed. The hydraulic data set of cross-hole test, which represents hydraulic property of in situ rock mass, is processed to evaluate a spatial distribution of hydraulic property by the multidimensional scaling (MDS) and the inverse distance weighted (IDW) interpolation. The reliability of this method is validated by numerical experiments using several continuum models with different hydraulic structures, and the applicability of the method is also examined by the field experiments.

View full abstract

This paper presents the outline of observational construction scheme employed for underground cavern construction, and of the Information and Communications Technology (ICT) as a technological tool to facilitate the observational construction. The Hokkaido Electric Power Co., Inc. has been conducting a Hydropower Project in Kyogoku, on the Pepenai and Bihinai tributaries of the Shiribetsu River in Hokkaido, Japan. The Kyogoku Hydropower Plant is the first pumped-storage hydroelectric power plant that was built by the Power Co. It will output a maximum power of 600 MW, with an effective head of 369 m and a maximum water usage rate of 190.5 m³/s. The power plant is housed in a large underground cavern of which the dimension is 45.8 m high, 24.0 m wide, and 141.0 m deep. Its total excavated volume is 116,000 m³ and the maximum cross-sectional area amounts to 1000 m². The geology in the vicinity of cavern belongs to a so-called “Green Tuff” region of the Miocene period, primarily composed of tuff breccia. The geology presents considerable challenges, including a distribution of tuff blocks and two major fault zones with a low uniaxial compressive strength, presumably due to faulting and hydrothermal alteration. Therefore, observational construction method was applied to the project in conjunction with other ICT-solutions, and the actual rock response during excavation was examined in order to ensure the optimum structural support for the cavern and construction safety.

View full abstract