1

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Yoshikazu YAMAGUCHISpeaker Dr. of Eng, Principal Researcher (Team Leader)

Dam Structures Research Team, Public Works Research Institute, Japan 1. INTRODUCTION

The first full-scale introduction of a modern CFRD undertaken in Japan as a permanent structure is the saddle dam at the Tomata Dam operated by the Chugoku Regional Development Bureau of the Ministry of Land, Infrastructure and Transport, Government of Japan. The construction of the dam was accompanied by detailed studies on the design and execution of modern CFRDs.

A typical cross section and a profile of the Tomata Saddle Dam are described in Fig. 1. To examine safety of the Tomata Saddle Dam, seepage/leakage and deformation have been measured with

gauges and sensors. This report presents the safety

evaluation of the Tomata Saddle Dam based on the measured results of seepage/ leakage through the body and its rock foundation, settlement of the dam body and deflection of a toe slab, that were carried out during the first filling of the Tomata Dam reservoir. 2. INSTRUMENTATION 2.1 OUTLINE OF MEASUREMENTS

Fig. 2 shows the purpose of the measurements at the Tomata Saddle Dam: 1) construction management during embanking, 2) safety management after completion, and 3) data acquisition for future design and research.

In this paper, we will introduce measurements for safety management of the Tomata Saddle Dam concerning seepage and deformation. 2.2 MEASUREMENT OF LEAKAGE/SEEPAGE

Measurements of leakage/seepage through the dam body and its foundation were conducted by dividing the dam body into five zones, and collecting the water in a measuring pit downstream from the drainage pipe as shown in Fig. 3.

Newly developed leakage detective sensors were installed in the slabs [1]. The leakage detective sensor applies electrical pulses to a twin-lead cable and observes the reflected waves to detect the location of leakage.

Fig.4 shows the appearance of the leakage detective sensor.

Fig.5 shows the leakage observation locations. The sensors were installed in the F11 slab, which is the longest slab in the Tomata Saddle Dam. 2.3 MEASUREMENT OF DEFORMATION

Measuring points were installed on surface of the dam to measure the exterior deformation, that is, horizontal and vertical deformations.

The deformation of CFRDs under water load is often measured by the face deflection. At the Tomata Saddle Dam, the face deflection was measured by the newly developed slide-type inclinometer on the longest slab, F11.

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Construction management in embankment Deformation of dam body Earth pressure

Examination of safety for seepage Seepage / leakage Pore water pressure in foundation

Measurement Safety management After completion

Examination of safety for deformation Deformation of main and toe slabs Exterior deformation of dam body Interior deformation of dam body

Data acquisition for design and research

Deformation of main and toe slabs Interior deformation of dam body Earth pressure Dynamic measurement

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LL11

LL22

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Downstream side

Upstream side

Flume

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Twin-lead cable (conductor)

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13m

m

Type CFRD

Height 25.00 m

Crest length 259.00 m Crest width 10.00 m

Slope Upstream 1:2.00 Downstream 1:2.00

2

3. RESULTS OF MEASUREMENT AND SAFETY EVALUATION 3.1 SEEPAGE/LEAKAGE

Fig. 6 shows the results of observations of seepage/leakage, reservoir water level, and rainfall. Seepage/leakage at the saddle dam ranged from 3.7 to 27.6 /min. The highest seepage/leakage observed was from 2.4 to 20.2 /min. at L-4. Inversely, at 0.1 /min., there was almost no leakage at L-1. The average of the observed seepage/leakage at the other drainage pipes was only 2 /min.

Temporarily high leakage occurred under the effects of rainfall, but at other times, its behavior was linked to fluctuation of the reservoir water level.

Considering the seepage/leakage by omitting the impact of the base flow (approx. 4 /min.) and of rainfall, the quantity produced by the reservoir is no higher than 20 /min., an extremely low value.

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(mm

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20

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(l/m

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170

180

190

200

210

220

230

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The measured results by the leakage defective sensors installed in the face slab F11 revealed the absence

of leakage caused by cracks in the slab. 3.2 DEFORMATION

The measured settlement at the top of the typical cross section of the dam was only 1.0cm during the first filling of reservoir. And the maximum deflection of the slab measured at EL.229.7m, which is the surcharge water level, was only 0.4cm. These valves of deformation are very small. 4. CONCLUSIONS

The results of overall evaluations including the results of measurements of seepage/leakage, deformation/deflection and of visual inspections confirm the safety of the Tomata Saddle Dam, which is the first full-scale modern CFRD in Japan. REFERENCE [1] Yamaguchi, Y. and Kobori, T. (2004): Development of Leakage Detective Sensor for Face Slab of CFRDs. ICOLD 72nd Annual

Meeting Workshop, W1-26-A011 (CD-Rom).

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:Leakage detective system

F11 slab

Main sensor cable

Top of dam

Sub sensor cable

Toe of dam