Project Subjects
Disaster Prevention and Maintenance for Hydropower Facilities
Background and Objective
Proper maintenance, renewal and operation of hydropower facilities are important in terms of provision
for global warming and stable electric power supply while the number of them constructed more than 50-60 years
ago is increasing. In recent years, deterioration of the facilities and changes which appear in environments surrounding rivers and forests along ones are remarkable, and the increase of the number and scale of disaster affectshydropower operations.
In this project, evaluation and analysis methods for existing dam structures will be established to securesafety against strong earthquakes considering ultimate and limit states of the structures. Also, techniques which
estimate points/places of sediment yield in dam basin and observe behavior of sedimentation and turbidity inrivers and reservoirs, and the simple analysis model which predicts sediment level and turbidity will be developed.

Main results
1. Seismic performance evaluation for aged dam structures
Static and monotonic loading tests of concrete gravity dam models (Fig. 1) were conducted focusing on
the fracture behavior at contact zone between dam and foundation. The test parameter was contact condition
between dam and foundation, and the loading condition was equivalent to the damʼs self-weight, water pressure
and seismic load. As the result, the stress and strain condition and the fracture behavior near the contact zone weredemonstrated.
Static and cyclic loading tests of spillway gate models (Fig. 2) were conducted focusing on the bucklingof primary members. The test parameter was truss shape between the strut arms. The models were subjected tohydrostatic and earthquake loads to investigate buckling modes, deformed positions and maximum strength. The
results will be utilized for evaluating the behavior of gates where primary members were buckled by using asimple seismic response analysis.
2. Development of observation technique and prediction model for sediments
New “Watershed Environment Database” was established for the analysis of sediment discharge fromforest roads and collapsed slopes. The database includes not only topographical and geological data above dambasins, but also the information of the degraded forest areas and the non-reforestation areas interpreted from satellite images, aerial photographs and ﬁeld observations.
In order to develop an evaluation method for slope stability along reservoirs, a soil-moisture monitoring
system which is composed of an electrical resistivity system and a soil-moisture sensor, was installed at the examination site at a hydropower station. This system was applied to visualize and analyze changes of soil-moisture
distributions under the slope ground (Fig. 3).
Also, in order to investigate processes of sedimentation and turbidity in reservoirs, a movable current
measuring system which equipped the Acoustic Doppler Current Proﬁler (ADCP) and the Global Positioning
System (GPS) were installed, and cross-sectional proﬁles of velocity were measured in a reservoir (Fig. 4). In
addition, two-dimensional numerical system was developed for estimating current and topography changes inrivers and reservoirs. These systems will be applied to ﬁeld measurements for understanding processes of sedimentation and turbidity.
Other reports
38[N10], [N09018]

Stable Power Supply Technology
Self weight

LoadingArmbracings

Loading
Dam
model

2.2m

Contact zone

1.5m

Strut armFoundationReservoir side of the gate
was vertically fixed on a test bed.
Fig. 2 Loading test of dam gate model
Test was assumed the axial buckling of strut arms
under water pressure and seismic load.

Model was fixed on a bed with PC anchors.
Fig. 1 Loading test of concrete gravity dam model
Test was assumed the damʼs deformation of downstream
direction under water pressure and seismic load.

Rate of resistivity change-100 -90 -80 -70 -60 -50 -40 -30 -20 -10

Moisture increase

10030405060

7080

Boreholeposition

3530

Scrap

2520

Moisture decrease

Cross-sectional profiles weremeasured along the cable-line
across the river.

20Changes causedby rainfall
infiltration fromthe surface

15(m)
(m)

1050-5-10

Slip surface（GL.-15m）-15-20
0

5

1015

20

25

30

35

40

455055

Radio-controlled boat withmeasurement instruments

Number of measure point
Fig. 3 Visualization example of soil-moisture distribution
Changes of soil-moisture distributions by the rainfall inﬁltrationfrom surface and the groundwater ﬂow from the upper slope wereanalyzed with an electrical resistivity system and a soil-moisturesensor.

Fig. 4 Movable current measuring system
The ADCP and the GPS were placed on a boat,and proﬁles of velocity, turbidity and topography in reservoirs were measured.

39