A Huge Pumped-Storage Hydroelectric Power Plant on the Kazuno River -Effective Head of 714 m-

INTRODUCTION

Construction work is now fully under way on the Kazunogawa Power Plant of Tokyo Electric Power Co., Inc., a pumped-storage hydroelectric power plant with maximum output of 1,600,000 kW, scheduled to go into service in 1999. The plant, an absolute necessity to enable the utility company to cope with the fast-increasing difference in power demand between daytime and night-time, is of particular interest, not only for the scale of power generation but also for the variety of construction work. A project outline and report on construction work are given below.

PUMPED-STORAGE HYDROELECTRIC POWER

PLANT

Generally, for pumped-storage hydroelectric power generation, dams are constructed both upstream and downstream on a river and connected with a headrace to generate electricity at a power station (usually constructed underground) between the dams. Water in the downstream dam is pumped to the upstream dam for storage using the excess electricity occurring at night, and power is generated at peak hours during the day for the adjustment of daily fluctuations in power demands and a stable supply of power. Although it is unclear where this idea originated, it is clear that the dam will be a life-saver in satisfying the massive energy demand of the huge Tokyo metropolitan area.

In contrast to the construction of a single dam at a fixed point, the power plant consists of upstream and downstream dams, an underground power station, and main/temporary tunnels networked to connect the dams and the station. Therefore, the construction work extends from a point through line and plane to space. Considering the limited construction sites and the fact that geological conditions are often difficult in Japan, it is easy to imagine the extraordinary efforts that were put into laying out these facilities. The dams, in a roughly straight line 5 km upstream and 3 km downstream from the power station, are regulating reservoirs in different river systems across a watershed. With an effective head of 714 m and a discharge capacity of 280 m³/sec, the power plant will generate an output of 160,000 kW at maximum using the world's largest reversible pump-turbines (400,000 kW x 4 units).

PROGRESSION OF MAJOR

CONSTRUCTION WORK

(1) Upstream dam

At the upstream dam's construction site, a 87 m high central diaphragm wall type earth fill dam with a dam volume of 4.06 million m³, about 20% of embankment work has been completed (Photo 1). Earth fill materials are taken from quarries, with close attention paid to the selection of quarries to protect the environment and preserve water quality. The experience and ingenuity of field engineers resulted in a design change to the longitudinal shape of the spillway to make it match the existing topography.

(2) Headrace

The main point of interest at the headrace site concerns the TBMs introduced to excavate the inclined shaft penstock. A preceding machine (pilot TBM, left in Photo 3) and a reaming TBM (right in the photo) used in combination advance at an inclination of 52.5 degrees. Structural concrete work of the water intake is about to start (Photo 3); standing in front of the intake convinces us of the vastness of power generation construction.

(3) Underground power station

A giant cavern, large enough to accommodate three jumbo jets, has been excavated about 500 m beneath the surface (Photo 5). Distinct from conventional underground construction sites, its cleanliness and explanatory signs posted in English for foreign visitors are very impressive. The site, situated in the easternmost part of the Shimanto strata which was formed about 65 million years ago, is not only a battlefield against initial ground stresses and rock joints built up since ancient times but also of great importance in demonstrating computerized construction with 1,300 sensors stretched all over the surrounding bedrock.

(4) Downstream dam

The downstream dam is a 105 m high gravity concrete dam with a volume of 620,000 m³. This downstream regulating reservoir is now under construction using RCD, a method of compacting no-slump concrete using vibrating rollers. Based on experience obtained from the construction of Sabigawa Dam, refinements were introduced into mix proportions, lifts, mixing and casting methods. Careful advance studies on these refinements suggest that they are building a reliable dam that will last many lifetimes with no spills. The site of the upstream dam looks like an extensive athletic field with heavy duty construction equipment going back and forth. In contrast to the upstream dam, cranes, tracks, plants and other facilities laid out in an orderly fashion, in a rather narrow valley await the placement of RCD (Photo 6).

Besides, the flood way and outlet on the downstream dam side, surge tank control facilities such as a cable shaft and substation, and temporary tunnels are now under simultaneous construction. Grouting work, protection work of excavated slopes, batcher plants and turbid water treatment plants are all progressing in many locations over the project site. The site is so vast that it takes a whole day to tour it.