Technical features on the renewal of large-scale prestressedrock anchors in Kawamata Dam foundation
H. Kawasaki

Japan Dam Engineering Center, Tokyo, Japan

T. Satoh, T. Nakazawa

Kinugawa Dam integrated management office, Ministry of Land, Infrastructure and Transport,
Utsunomiya, Japan

Y. Hashira

Obayashi Corporation, Tokyo, Japan

ABSTRACT: Kawamata Dam is a concrete arch dam with 117 m high which was completed in
1966. A huge underground transmitting wall for sustaining the arch thrust force was constructedin the left bank bedrock. In addition , the world largest class prestressed (PS) anchors by total
capacity in that time were installed for the purpose of tightening this wall along with too many
existed nearby high-angle faults , stabilizing of the bottom of slope and prevention for the surface
loosening. Additionally, big retaining walls were constructed to support PS anchors as pedestals.
These structures are called bedrock PS works. However, after passing of 50 years, deteriorationof PS anchors was confirmed by irregular behaviors observed in measured values, and damages
in anchor heads found by integrity surveys for PS anchors. After these anomalies were checkedby the technical committee, the renewal plan by the full installation of PS anchors and the repairment of the retaining wall was determined in 2013. From 2014 to 2016, additional surveys, thedesign of PS anchors for the renewal and detailed construction planning was implemented.
The content of the renewal plan consists of a total number of 124 units of PS anchors with
2352 kN/unit of anchor load, and the repairment of the right bank retaining wall. According tothis design, as the first phase renewal, 59 units of PS anchors were installed at the location ofrock foundation of Kawamata Dam until 2021. The renewal works were executed under very
strict site condition such as the steep and deep cliff terrain, no access ways, very hard rockfoundation, frozen condition in winter and flood discharge during flood season. On the other
hand, many technical developments were achieved using the latest technology, such as staging along cliff, tools and materials, corrosion protection, drilling in hard rock, tendon setting,grout mix, tensioning method, quality control, measuring instrument, maintenance method,and others. As a result, this works laid the basis of PS anchor technology for dams in Japan.
We describe the judgement renewal decision-making and the main technical points of thedesign and construction, mainly concerning to the PS anchors reinforcing the rock foundation.

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1 OUTLINE OF BEDROCK PS WORKS IN KAWAMATA DAM
1.1 Bedrock PS works at the time of dam construction
The bedrock PS works in Kawamata arch Dam (117m high) to reinforce the rock foundationconsists of a 70m high underground transmitting wall to transmit the huge thrust force deep to theleft bank, large scale PS anchors with the large-capacity of 1372～2352KN ×162 anchors andhorizontal long-length of 40～70m, and two big retaining walls.
These structures were originally constructed in 1962-65. Its design method was presented at
the 1965 ICOLD conference in Edinburgh by Ministry of Construction, Japanese Gov., whichwere acclaimed as a breakthrough method to reinforce dam foundations. The bedrock PS works
include three parts of PS anchors. A part anchors penetrate and tighten the transmitting wall andmany high-angle faults, B part anchors support the big retaining wall at lower elevation of the leftbank, and C part that anchors prevent loosening of the right bank.
The site plan and specifications of these foundation works are shown in Figure 1.
2352kN x 66 anchors
Renewal: 2352kN x66

Lake Kawamata

A part anchor

Transmitting wall

Retaining wall

C part anchor
1470kN x36 anchors
Renewal: 2352kN x23

Rocky pillar mass
area consisting ofhigh angle faults

B part anchor
1372kN x60 anchors
Renewal: 2352kN x35

Figure 1. Plan of Kawamata Dam, transmitting wall and PS anchors in rock foundation

1.2 Renewal of bedrock PS works
Several measurements such as displacements in the bedrock foundation were continued for about
10 years after the dam completion, and no anomalies were found. However, due to concerns about
deterioration over time, in 2004 when 40 years passed after the dam completion, rock displacement sensors were re-installed at 12 sites (8 at left bank and 4 at right bank ).
After several years, some measurement values revealed stair-like behaviors of displacement in
the bedrock near the transmission wall, which was interpreted as the gradual break of a tendon
with six PC steel bars. Corresponding to this, the integrity surveys were conducted in 2011-2012,
it was found that some tendons of PS anchors were rather deteriorating by corrosion, and threehorizontally long cracks in the right retaining wall were opening.
Thus, the technical committee for Kawamata bedrock PS works was held in March 2013 andjudged the renewal by full installation of PS anchors and the repairment of the right bank retaining
wall. The renewal PS anchors are a total number of 124 units of PS anchors with design anchor
load 2352 kN/unit of and anchor length of 40~70 m.
From 2013 to 2016, additional surveys, anchor renewal design and field tests by prior anchor
installations were carried out. As a result of the detailed consideration on PS anchors, as shownin Figure 2, the renewal anchors are placed in the center of elevation to existing anchor rows.
Also, on the premise that the existing anchors will deteriorate in the future, the renewal anchors
were decided to set the same total load as at the time of construction for each section of A part, B
part, and C part. Further, in order to improve construction efficiency, all design loads were unified
to 2352 kN/unit, of which drilling diameter is 216 mm.

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Downstream view
Kawamata arch
dam body

Transmitting wall

Cross section view
EL944.0m: A part 6th row
EL932.0m: A part 5th row

Transmitting
wall
th

6 row

10°★ EL918.5m: A part 4 rowthGG5

5th row

C6

EL902.5m: A part 3rd row

4th row

EL893.5m: A part 2nd row
70m

2nd row30°

3rd row★ B part 3rd row

GG6existing anchors 1st row

First phase A part anchors
First phase B part anchors
Second phase anchors

56.5m

EL879.0m: A part 1st row
B part 1st row★Multistage bedrock strain meter★Multistage bedrock displacement meter

Figure 2. Downstream view and Cross section view of left bank on PS anchors and transmitting wall
Drone view from lower stream

View from upper stream
Staging onright bankArch dam body
Staging onright bankStaging onleft bankStaging onleft bankFigure 3. Situation of Kawamata Dam under the renewal works in 2019

In the renewal design, the design load was decided at 2352 kN/unit which is the same as theconstruction time, to balance with the existing PS anchors. The first phase renewal was executedfrom 2017 to 2021, and 59 PS anchors, about half of the total 124 anchors, were renewed. Figure
3 shows the working situation on the downstream of the dam. Main materials and machineries
were transported by a 4.5-ton cable crane.
On the left bank, due to the steep topography, large-scale temporary construction platforms
were installed at each elevation of the PS anchor stage using a sub-tower crane. The right bankwas not as extensive as the left bank, but taller scaffolds were erected. Then, very large amountof cement milk(Figure 8) was injected to fill the gap below the back of wall before the anchor
works. This bonding of the wall and rock was very effective to stabilize the steep cliff.
1.3 Anti-corrosion protection on tendon
The tendon as an anchor unit consists of 14 PC steel strands with the diameter of 15.2mm.
As for anti-corrosion, targeting 100 years of durability, the full-bonded type which fills alllength of tendon by grout was adopted, and it was combined with ECF (Epoxy Coated and Filled)strands (Figure 5) as the double anti-corrosion structure.
After 60 years of the Kawamata Dam construction, the integrity surveys showed obviously thatthe full-bonded type was more durable, because the corrosion of the full-bonded type adopted toexisting anchors was quite less than other anti-corrosion measures.
In anticipation of long-term durability, the quality of grout is also very important. Therefore, a
new non-shrink grout was developed for the renewal of PS anchors.

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About grout injection, it requires a long distance of 80m pumping with a height difference 90m
due to construction site conditions, and there were concerns about segregation and cracking. So,
to achieve both high fluidity and non-shrinkage, a composition with combination of grout milk,
high-performance AE water-reducing agent and expanding agent for the grouting material wasused. The trial was repeated to derive the optimum addition amount and it was completed asshown in Figure 4.
Internal filling type epoxy resin coated PC strand
Silica sand was embedded in the epoxy resin
surface to improveadhesion with grout.

Table of grout composition
Ordinary High efficiency Air
Bulkage
Portland
Entraining water
admixture
cementreducing agent

1,423㎏／m

3

22.5㎏／m

3

C：W
3

74.9㎏／m 1：0.35

Figure 4. Anti-corrosion protection by ECF strand and super high-quality grout

2 INTEGRITY SURVEY ON ANCHORS
Various integrity surveys such as the one summarized in Table 1 were conducted and confirmedthat some PS anchors have significantly deteriorated. In particular, the deterioration of the unbonded anchors on the right bank was progressing, and a decrease in tension was also observed.
On the other hand, the deterioration of left bank anchors at the full-bond type was limited, but
pitting corrosion leading to delayed fracture was observed (Fig. 5), the measured values of rockdisplacement showed step-like movements, and 60 years had passed since anchor installation.
Considering these together, a policy of full renewal of the PS anchors was decided in 2013.
Table 1. Results of integrity surveys to existing anchors
1. Left bank A part (PC steel bar, bonded type)a. Drilling visual inspection and ultrasonic measurement (on steep slope surface): Deterioration could not be visually confirmed. Detected there were voids around the steel bar by ultrasonic measurement on steel bar head.
b. Anchor exposure in GG6 pit: Confirmed traces of water infiltration in the mortar around the steel bar. Confirmed partial surface rust and pitting corrosion on the surface of the steel bar confirmed.

2. Left bank B part (PC steel wire, bonded type)a. Visual and endoscopic: Confirmed significant head defects at the bottom place near the water level.

3. Right Bank C part (PC steel wire, unbonded type)a. Visual and endoscopic: Confirmed breakage of the highest row anchor and progress of corrosion of PC steel
wires in the hole. Confirmed significant deterioration of the head cover concrete in several anchors.
b. Lift-off test (20 anchors): Confirmed serious reductions in tensile load, several anchors showed softening.

4. Fracture surface of PC steel wire or bar

a. Observation of PC steel wire: Confirmed the main causes of fracture are the cross-sectional area reduction
b. Observation of PC steel bar in the other dam: Confirmed delayed fracture due to corrosion
Tensile test: Confirmed a significant decrease in elongation capacity of PC steel bars

A partA partAnchors at Grout tunnel

A partPhenolphthalein reaction

pitting holes on steel bars

After chipping out

Figure 5. Pitting corrosion on a tendon at Grout tunnel and surface looks in an existing anchor

3
3.1

DESIGN FOR REINFORCEMENT OF ROCK FOUNDATION
Stability check of rocky pillar mass報1-28

In left bank of Kawamata Dam, there are many high-angle faults called rocky pillars (hereinafter RP), which needed to be reinforced as the massive rock foundation of the Arch Dam.
At the time of construction, two-dimensional model experiments were conducted using gypsum
and photoelasticity, and it was found that a transmitting wall (hereinafter TW) was effective inenlarging the shear sliding zone, and that the stress near TW was reduced. However, since it was
shown that tensile stress almost perpendicular to the TW occures widely, strong tensioning in thewide area was needed to tighten and integrate the whole of RP mass including TW.
Figure 6 is the simplified 3D model separated by F30 and F1 including TW and PS anchors to
reproduce the stability calculation at the time of construction. By using this model, the importanceof TW and integration of RP mass by PS anchors was reconfirmed.
N = (τR･AR + f･ΣW + τF･ΣAF) /H

Upper stream

N: Safety Factor,
H: Sliding Force of RP mass
τR: Shear Strength of RP bottom
AR： Area of RP bottom
f: internal friction coefficient of RP bottom
ΣW: Weight of RP
τF: Shear Strength of F1 back side
ΣAF: Area of F1 backside

EL.960m

ArchthrustTW
RP bottom

TW: Transmitting wall
RP: Rocky Pillars

EL.910m

Figure 6. 3D model for Stability calculation of Rocky Pillar mass in Kawamata Dam left bank

3.2

Confirmation of Prestress in bedrock inside

Figure 7 shows the results of pseudo-three-dimensional analysis of three elevations on the left bank.
As the characteristic of PS anchors, prestress (compression stress) strongly occurs around the headand bottom, but prestress around the center is weak. So, the PS anchors were densely arranged inrows so that the prestress around TW was kept high by the group anchor effect.
However, since the prestress is dissipated on the tip of TW, an intermediate load removing
method to generate strong prestress developed. This method to increase prestress can suppress theformation of a gap between the tip of TW and the bedrock.
A part anchors at EL.932.0m

F30ting wall)

Arch

TW

Arch thrust

A part anchors at EL.879.0m

Arch thrust

Tip← Compression kN

Anchor bottom
2.5m pitchTW

F1

PS anchor area

A part anchors at EL.902.5m
Tip

3D model diagramat EL.902.5m:
model projected
topographical andgeological conditions in the vertical direction

TW

Arch thrust

Figure 7. Compression stress distribution on slice plan by 3D FEM analysis of Rocky Pillar mass

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← Compression kN

TW(transmit-

F30

Anchor bottom
2.5m pitch

Anchor bottom
2.5m pitch

Tip← Compression kN

Inside of bedrock4 MAIN SPECIFICATIONS OF RENEWAL PS ANCHORS
By the design of renewal PS anchors, design load, ultimate and acceptable strength, PC material, number of PC steel strands per tendon, bond length, diameter and so on were decided.
Table 2 shows the calculated results according to the design. La is calculated by τu which means
ultimate bond strength between grout and rock, and τu was determined to be 1.0 N/mm2 according
to the results of the field pull-out test at the Kawamata Dam site. Lb is calculated by τba whichmeans ultimate bond strength between grout and tendon, and τba was determined to be 1.0 N/mm2
from a corresponding value to the grout compressive strength of 30 N/mm2 in the design standards
in Japan. Eventually, larger value of La and Lb is adopted as the bond length.
Table 3 shows specification of anchors or building-use anchors in Japan. Though these manuals
are made for the soil anchor, we applied them, also referring to overseas manuals on PS anchors.
Actually, the rock anchor manual in Japan was issued in 2021 right after the first phase renewal.
Table 2. Necessary bond length (m) by calculation result of the renewal anchors
Construction point

Left bank A part

Left bank B part and Right bank C part

14
287
9.646
8.362
9.646
10.0

14
295
7.074
8.136
8.136
8.5

Number of PC steel strands per tendon
U: Perimeter around tendon (m)La: Necessary bond length (m) to τu
Lb: Necessary bond length (m) to τbaLarger value of La and Lb (m)Round up value of bond length (m)Grout design standard strength(N/mm2)30

Table 3. Specification of anchors: Number, Design Load, Bore diameter, Bond length, etc.
Construction point

Left bank A part

Number of Anchors

66

Left bank B part

Right bank C part

35

23

Design Load (KN）

2,352 (same as original load 240tonf x 9.8)

Safety factor(Fs）3 (safety side value same as building ground anchor in Japan)

Anchorplacement

Pitch of anchors(m)2.5

Declination angle （ ° ）in drilling hole

Bore diameter (mm)

6.0

3.0

Horizontal angle:0
Horizontal angle:0
Horizontal angle:10
Vertical angle: 10
Vertical angle: 30
Vertical angle: 20
216 (actual maximum size in Japan’s anchors)
72.9

Maximum anchor length (m)2.5 or34.2

50.0

Down-the-hole hammer (pneumatic type) / RPD skid type

Drilling method / Machine type

Height of Retaining wall is 74m
C part 8th row (EL.950.0m）
C part 7th row

C part 5th row
C part 4th row

＠8000

C part 6th row

C part 3rd row

Cracking lines

C part 2nd row
C part 1st row (EL894.0m）○

Existing anchor■ 1st Phase anchor▲ 2nd phase anchor

Slash grout by boring●; more than 50kg/m●; more than 20Lu

Figure 8. Front view of Right bank C part anchors, crack lines and quantity of grout injection

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5 RENEWAL WORKS OF PS ANCHORS
5.1 Repairment of the right bank retaining wall
Figure 8 shows the front view of the right bank of C part anchors, the crack lines confirmed byvisual inspection, and quantity of grout injection.
There are three horizontal cracks in the middle to low elevations of the right bank retaining
wall, and a boring survey confirmed that there were gaps between the retaining wall and the bedrock. So, Large amount of slush grouting (10m depth in bedrock) was conducted to the entire
backside of the retaining wall to integrate the bedrock and the retaining wall. This works alongwith slope protection works and prior to the PS anchor works were done from October 2017 toJuly 2018.
From August 2018 to August 2020, 6 stages (15 anchors) out of 8 PS anchor stages (23 anchors)
were installed in the first phase renewal. Also, since there were no drainage holes, 10 drainage
holes were installed around the renewed anchors on the middle and lower elevations.
Eventually, these works greatly improved the safety of the right bank.
5.2 Construction of large-scale staging on steep cliff
A large-scale work staging platforms covering a steep cliff were erected to install PS anchors.
Regarding the structure of the left bank work platform, the first and third rows of the low-elevation
parts are less impact of water discharge from dam and in order to install the anchor during thenon-flood season when construction is possible, A bracket structure in which each row of work
platforms are independent, was adopted.
The system scaffolding was set up from the third stair bracket work platform. The structure of
the right bank work platform is a system scaffolding, and the scaffolding was set up from lower
to upper when slash grouting was performed before installing anchor. At the time of anchor work,
the system scaffolding was dismantled for each anchor work step (8m).
Figure 9 shows the staging by work platforms on both banks, respectively.
Left bank
bank
Left

Right bank

8th work platform

6th work platform
5th work platform
4th work platform
3th work platform

Figure 9. Large-scale Staging by work platforms on the left bank and right bank

5.3 High accuracy of solid rock drilling
The drilling diameter of the anchor for this work is as large as 216 mm, and the maximum drilling
length is 72.9 m. Since the in-situ bedrock were very hard ranging from CH to B class, A down-thehole hammer (hereinafter DTH) capable of high-speed drilling on workability, and a skid type improved for easy decomposability to transport by a 4.5-ton cable crane was chosen. In particular, we
took the following technical measures to achieve high-precision drilling during high-speed drilling foranchors of large-diameter and long.

5.4 Ingenious initial drillingAt the initial drilling that affects the drilling accuracy, by using the DTH from the beginning, it
becomes difficult to secure drilling accuracy due to thrashing of the bit tip at the beginning ofdrilling. Therefore, a 2.6m long rod was pre-drilled with a non-impact rotary boring machine thatwas less prone to blurring and misalignment and used as a guide hole for drilling by DTH.

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The measurement results at 2.6m and 5.0m from the hole mouth with the drilling angles at A
part, B part and C part (see Fig.1) of 0.27°, 0.13°, and 0.23° on average, respectively and only aslight increase in the drilling angle, were analyzed. The initial drilling accuracy, which greatly
affects the final hole bending accuracy, is ensured just by doing so. In addition, assembling workfor the down-the-hole hammer drilling machine had been going smoothly.
5.5 Drilling management
In the largest hard rock drilling in Japan, to obtain dynamic information during drilling immediately, ground exploration sounding device was attached to the drilling machine. And then, we
obtained data quantitatively such as machine rotation torque, striking pressure, water pressure anddrilling speed in real-time and grasped the characteristics of bedrock (Fig. 10a).
The drilling accuracy of all holes was confirmed at the middle point of drilling, using during
drilling measurement device with a gyro and an acceleration sensor. In addition, the full-length
measurement was also carried out for 10% of installed anchor (Fig. 10b).
Table 4 shows the measurement results of hole bending. Accuracy confirmation during drilling
enables early detection of an increase in hole bending and countermeasures against defects. Therefore, it was a useful means of construction management based on the suppression of process delays.
Measurement monitor

Monitor screen

a.Drilling situation by ground exploration technology

b.Measurement circumstance of hole bending

Figure10. Drilling and measurement
Table 4.

Unit:mHole bending measurement results

Horizontal distance
Vertical downward
measurement result(Difference from design)
Increment per m

5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 69.0
0.10 0.14 0.19 0.25 0.32 0.40 0.50 0.61 0.72 0.83 0.97 1.10 1.25 1.36
0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.03

5.5.1 Observation in the underwater borehole
After completion of drilling, the underwater hole wall was directly observed by a camera system,
which was developed to capture clearer photographs even under turbid water. These accurate
geological characteristics were reflected in the form of 3D information of geological map. Using
obtained geological map, we aimed at reducing hole bending by controlling the drilling speed
based on the geological data. Figure 11 shows the geological map by the camera observation.
Rock classification at the design stage
Concreteclass CL
class CM/CH bedrock(transmitting walls）
bedrock
Borehole camera observation image (development view of bore hole wall)class CM/CH
class CL
Concrete
45

44

43

42

41

40

39

38

37

36

35

34

class CL bedrock

Unit:mclass CM
33

32

31

Figure 11. Bore hole wall confirmation diagram by underwater borehole camera system

5.5.2 Drilling management by CIM
The centralized data management was performed using CIM (Construction Information Modeling) such as drilling information and hole bending data acquired by ground exploration technology, borehole wall observation and so on. It achieved high-accuracy drilling by reflecting thedrilling data of peripheral holes. Eventually, it enabled more accurate drilling to avoid interference with other underground structures (Fig. 12).

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Avoidance ofinterference

Virtual view
looking into
the bottom
accuracy
control
by CIM

Figure 12. Quality control on drilling by information modeling system

5.6 Tensioning management
In tensioning work, when the amount of elastic displacement is large, the stroke of the jack isinsufficient with a conventional single tensioning jack, and replacement work is required.
Therefore, a large jack coupling system was devised that couples 2 or 3 jacks according to theanchor length, enabled to tension work without replacing the tension jack. In addition, we confirmed that the measurement results of the load-displacement in real time using the tension control
system. We achieved high-accuracy tension control by combining these technologies (Fig. 13).

Figure 13. Triple coupled large tension jacks and tension control system

5.7 Lifting equipment for transportation of long-size tendons
Tendons must be transported in such a way that the twisted, sharply bent, adhered with harmful
substances, or damaged in anticorrosive materials, which are not damaged. The tendon of thisproject is about 50m long and weighs about 1 ton, so its handling is not easy.
In addition, the site condition is not suitable for tendon transporting by hanging from its assembly yard. Therefore, in transporting tendons, we developed a semi-circular characteristic
hanging tool that makes the tendon curve smoothly so that no concentrated load is generated on
the suspension part, and the tendons were transported by folding it in two or three (Fig. 14).

Lift shortage

Characteristic
hanging tool

Figure 14. Tendon transport lifting tool

5.8 High-pressure resistant cloth packers
A packer is an indispensable tool, because of enough injection to the bond length in grout injection
under pressure, and suitable tension fixing of a tendon after grout hardening (Figs. 15a). Because
the above-mentioned intermediate unloading method requires two packers for a short section, it
was desired to make it significantly lighter than the conventional steel rubber packer. However,product cloth packers were only available up to a diameter of 165mm, so we developed a cloth
packer with a large diameter and high-pressure resistance.
For development, we confirmed its performance that abrasion resistance and pressure resistance due to differences in material quality. Further, installation method, performance tests,

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wearing tests, practicality confirmation tests, etc (Figs. 15b) were conducted.
In the on-site pull-out test at Kawamata Dam, a cloth packer was used, and there was no problem such as grout leakage even under high pressure. In addition, though the pull-out resistanceincreased greatly, it was presumed that these values were affected using the cloth packer. Namely,when grout is injected, the grout in the cloth packer is concentrated by removing only water
through the special fabric as pressure increases, resulting in high strength.
TendonBore holewall
Packerinjection

Tensioning
Bond lengthpressurization
injection

Cloth packer

a. packer method of full-bond typeb. High pressure resistant cloth packer
Figure 15 Development of cloth packer on full bonded type anchor

6 HIGH-PERFORMANCE MEASUREMENT FOR SAFETY
As for measurement of anchors and bedrock, many instruments such as “anchor load; 17 (25)units, bedrock strain; 5 (9) units, and rock displacement; 3 (4) units” were installed by the firstphase renewal. Numbers inside of parentheses show the total number of the units.
Anchor load is particularly important, but until now, its measurement in full bonded type anchors has been considered difficult. However, in Kawamata Dam, we developed “axial force
measuring strand” which is a steel strand in a sheath and has small load cells on the anchor head.
This instrument is placed inside the tendon and has so far stably captured anchor loads linked tothe change of seasonal temperature and reservoir water level.
Next, as for bedrock strain, the A part anchor has an important role in introducing prestressaround the transmitting wall. So, "strain measuring anchor" was developed that is installed very
close to the targeting anchor and can measure a slight strain change in the rock mass. This instrument proved the effectiveness of the intermediate load-removing method by measuring very slightstrain changes and residual prestress generated by anchor tensioning. Further, the depth-dependent rock displacement meter measures the rock displacement according to five depths, and it isconsidered to be effective when displacement occurs due to anchor fractures or earthquakes.
These measurements are planned to continue until 100 years from now. So, the long-term durable measurement methods such as the vibrating string type were adopted.
7 CONCLUSIONS
After passing of 50 years, deterioration of PS anchors was confirmed by irregular behaviours inmeasured values, and damages in heads were found by integrity surveys for PS anchors. So, therenewal project by the full installation of PS anchors and the repairment of the retaining wall wasstarted in 2013. The renewal plan consists of the installation of total 124 unit of PS anchors
and the repairment of the retaining wall. In the first phase renewal until 2021, 59 units of PS
anchors were installed and the right bank retaining wall was stabilized by grout injection.
Through the experiences of Kawamata Dam and others, “Design and construction manualof PS anchors for dam” was issued in 2021.9. At the present, the second phase renewal is underconsideration, and further improvements by this manual will be made as appropriate.
REFERENCES

Japan Society of Civil Engineers, 1965, project report Kawamata Arch Dam (in Japanese)
Ministry of Construction, Japanese Government, 1965, Foundation Treatment of Kawamata Dam, Proceedings of ICOLD conference, Edinburgh
Japan Dam Engineering Center, 2021, Design and construction manual of PS anchors for dam (in Japanese)

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